The Wrist and Hand

 

 

 

Dorsal Approach to the Wrist

Applied Surgical Anatomy of the Dorsal Approach to the Wrist Volar Approach to the Distal Radius

Volar Approach to the Carpal Tunnel and Wrist Volar Approach to the Ulnar Nerve

Applied Surgical Anatomy of the Volar Aspect of the Wrist Volar Approach to the Flexor Tendons

Midlateral Approach to the Flexor Sheaths, Proximal and Middle Phalanges

Dorsal Approach to Phalanges and Interphalangeal Joints Applied Surgical Anatomy of the Finger Flexor Tendons

Vascular Supply of the Tendons

Volar Approach to the Scaphoid Dorsolateral Approach to the Scaphoid

Drainage of Pus in the Hand

Optimum Operative Conditions

Drainage of Paronychia

Drainage of a Pulp Space Infection (Felon) Web Space Infection

Anatomy of the Web Space of the Fingers Anatomy of the Web Space of the Thumb

Adductor Pollicis Muscle

First Dorsal Interosseous Muscle Arteries

Tendon Sheath Infection Deep Palmar Space Infection

Drainage of the Medial (Midpalmar) Space Drainage of the Lateral (Thenar) Space

Applied Surgical Anatomy of the Deep Palmar Space

Lateral Space (Thenar Space) Medial Space (Midpalmar Space)

Drainage of the Radial Bursa Drainage of the Ulnar Bursa Anatomy of the Hand

Palm

Dorsum of the Hand

 

Eighteen approaches to the wrist and hand are described in this chapter: Two to the wrist, two to neural structures crossing the wrist, two to the flexor tendons, two to the scaphoid, one to the phalanges and interphalangeal joints, and nine approaches required for the drainage of sepsis in the hand.

The dorsal approach to the wrist joint is used mainly for treating rheumatoid arthritis, open reduction and internal fixation of distal radial fractures and surgery on the bones of the carpus; the volar approach to the

wrist is used for fixation of distal radial fractures. The volar approach to the carpal tunnel is used primarily for exploring the carpal tunnel and its enclosed structures but can also be used for fracture fixation. The applied anatomy of each approach is considered separately in this chapter.

The volar approach to the flexor tendons is used most often in hand trauma. It also provides excellent exposure of the digital nerves and vessels. The midlateral approach is useful in the treatment of injuries to the digital neurovascular bundles and also phalangeal fractures. A discussion of the applied anatomy of the finger flexor tendons follows the description of these two approaches in this chapter.

Dorsal and volar approaches to the scaphoid are outlined together, with a brief description of the blood supply of that bone.

Infection within the hand is a common clinical problem. Although early diagnosis and the use of intravenous antibiotics have reduced the number of cases of hand sepsis requiring surgery surgical intervention is still necessary in many cases to avoid permanent disability. The methods of drainage used for these conditions are described together, with an introduction to the general principles of drainage in the hand. Of all the infections of the hand that require surgery, paronychia and felons are by far the most common.

Throughout this book, we have related anatomy to surgical approaches. In the hand, however, the majority of wounds encountered arise from trauma, not from planned incisions. A brief review of the overall anatomy of the hand is vital to explain the damage that may be caused by a particular injury. Although clinical findings are the key to the accurate diagnosis of tissue trauma, knowledge of the underlying anatomy is crucial in bringing to light all possibilities and minimizing the risk that a significant injury will be overlooked. For example, arterial hemorrhage from a digital artery in a finger nearly always is associated with damage to a digital nerve, because the nerve lies volar to the severed artery. Arterial hemorrhage in a finger should alert the surgeon to the possibility of nerve injury, which often appears clinically as a change in the quality of sensation rather than as complete anesthesia, and can be overlooked in a brief examination.

Therefore, this chapter ends with a section on the topographic anatomy of the hand. This information is presented in one section rather than on an approach-by-approach basis to provide a clear and integrated picture of hand anatomy.

Dorsal Approach to the Wrist

The dorsal approach provides excellent exposure of all the extensor tendons that pass over the dorsal surface of the wrist. It also allows access to the dorsal aspect of the wrist itself, the dorsal aspect of the carpus, and the dorsal surface of the proximal ends of the middle metacarpals. Its uses include the following:

1. Synovectomy and repair of the extensor tendons in cases of rheumatoid arthritis; dorsal stabilization of the wrist1,2

2. Wrist fusion3

3. Excision of the lower end of the radius for benign or malignant tumors

4. Open reduction and internal fixation of certain distal radial and carpal fractures and dislocations, including dorsal metacarpal dislocations, displaced intra-articular dorsal lip fractures of the radius, and transscaphoid perilunate dislocations. A variety of approaches are possible depending on the anatomy of the fracture to be treated. Access to the intermediate and radial columns of the distal radius will be described. Plates applied to the dorsal surface of the distal radius frequently cause irritation to the numerous extensor tendons that pass over their surface.4 For this reason, volar approaches are now often preferred for plate fixation of fractures of the distal radius.5

5. Proximal row carpectomy6,7

 

Position of the Patient

 

Place the patient supine on the operating table. Pronate the forearm and put the arm on an arm board. Exsanguinate the limb by applying a soft rubber bandage, and then inflate a tourniquet (Fig. 5-1).

 

Landmarks and Incision

Landmarks

Palpate the radial styloid, the most distal extension of the lateral side of the radius.

Palpate the ulnar styloid on the dorsal aspect of the distal end of the ulna.

 

 

Figure 5-1 Place the patient supine on the operating table. Turn the forearm downward and place the arm on a board, for the dorsal approach to the wrist joint.

 

Incision

Make an 8-cm longitudinal incision on the dorsal aspect of the wrist, crossing the wrist joint midway between the radial and ulnar styloids. Begin the incision 3 cm proximal to the wrist joint and end about 5 cm distal to it. It can be lengthened if necessary (Fig. 5-2).

Because the skin on the dorsum of the wrist is pliable and redundant, the healed incision does not cause a contracture of the wrist joint, even though it crosses a major skin crease at right angles.

 

Internervous Plane

 

There is no true internervous plane because the extensor muscles whose tendons are separated share a common nerve supply from the posterior interosseous nerve. Because these muscles receive their nerve supply at the level of the elbow or just below it the intermuscular plane between them can be used safely.

 

Superficial Surgical Dissection

 

Incise the subcutaneous fat in line with the skin incision to expose the

extensor retinaculum that covers the tendons in the six compartments on the dorsal aspect of the wrist (Fig. 5-3).

 

Deep Surgical Dissection

 

The deep dissection depends on the procedure to be performed. Four techniques will be described.

Synovectomy

Incise the extensor retinaculum over the extensor carpi radialis longus and brevis muscles in the second compartment of the wrist. The compartment is on the radial side of Lister tubercle. To expose the other compartments, incise the ulnar edge of the cut retinaculum by sharp dissection in an ulnar direction to deroof sequentially the four compartments on the ulnar side. Then, dissect the radial edge of the cut extensor retinaculum radially to deroof the first compartment. The extensor retinaculum should be preserved; during closure, it can be sutured underneath the extensor tendons to prevent them from being abraded by the bones, which can be deformed grossly by rheumatoid arthritis (Fig. 5-4).

Exposure of the Intermediate Column of the Distal Radius

Identify the tendon of the extensor pollicis longus by palpation using Lister tubercle as a guide. Incise the extensor retinaculum using an angled incision overlying the tendon to open the third extensor compartment. Gently mobilize the tendon of extensor pollicis longus and retract it radially using a vascular loop. Elevate the fourth compartment subperiosteally leaving the compartment itself intact. The intermediate column of the distal radius is now exposed. If access to the joint is required make a small transverse incision into the wrist joint capsule. Suturing the retinacular incision underneath the tendon of extensor pollicis longus will protect the tendon from abrasion between the tendon and underlying plate (Fig. 5-5).

 

 

Figure 5-2 Skin incision for the dorsal approach to the wrist joint. A cross section at the distal portion of the radius is seen.

 

Exposure of the Radial Column of the Distal Radius

Gently retract the radial side skin flap to expose the extensor retinaculum covering the first compartment. Palpate the tendons of extensor pollicis brevis and abductor pollicis longus and incise the retinaculum at the musculotendinous junction of these two muscles. Retract the two tendons radially to expose the radial column of the distal radius (Fig. 5-6).

Full Exposure of the Wrist Joint

This exposure is usually used for arthrodesis of the wrist joint and is not used for fracture reduction and fixation. Incise the extensor retinaculum over the extensor digitorum communis and extensor indicis proprius tendons in the fourth compartment of the wrist. Mobilize the tendons of the compartment, lifting them from their bed in an ulnar and radial direction to expose the underlying radius and joint capsule (Fig. 5-7). Incise the joint capsule longitudinally on the dorsal aspect of the radius and carpus (Fig. 5-8). Continue the dissection below the capsule (the dorsal radiocarpal ligament) toward the radial and ulnar sides of the radius to expose the entire distal end of the radius and carpal bones (Figs. 5-9 and 5-10).

The tendons of the extensor carpi radialis longus and brevis muscles, which attach to the bases of the second and third metacarpals and lie in a tunnel on the radial side of Lister tubercle, must be retracted radially to expose fully the dorsal aspect of the carpus.

 

 

 

Figure 5-3 Skin flaps are developed, and the extensor retinaculum is visualized in the deeper portion of the wound. Cross section reveals the approach to the fourth tunnel, which contains the extensor digitorum communis and the extensor indicis proprius.

 

 

Figure 5-4 A: For synovectomy, make an incision over the second compartment. B: Open each of the compartments sequentially from radius to ulna by incising the septum that connects the retinaculum to the carpus itself and the joint capsule. C: Now that the compartments have been deroofed, place the retinaculum between the extensor tendons and the distal ends of the radius and ulna to provide added protection for the tendons.

 

 

Figure 5-5 Enter the wrist joint by making a small transverse incision in the wrist joint capsule. The intermediate column of the distal radius and the lunate are exposed.

 

 

Figure 5-6 Retract the tendons of extensor pollicis brevis and abductor pollicis longus radially to expose the radial column of the distal radius.

 

 

 

Figure 5-7 The retinaculum over the fourth compartment has been opened, revealing the communis tendons.

 

 

Figure 5-8 The extensor communis tendons and extensor indicis proprius have been retracted, revealing the dorsal radiocarpal ligament and the joint capsule, which then is incised.

 

 

 

Figure 5-9 The dorsal radiocarpal ligament and the extensor tendons are elevated from the posterior aspect of the radius to expose the entire dorsal end of the bone.

 

 

Figure 5-10 The extensor tendons in their compartments have been elevated to expose the distal end of the radius and ulna.

 

 

Dang

 

 

Nerves

The radial nerve (superficial radial nerve) emerges from beneath the tendon of the brachioradialis muscle just above the wrist joint before traveling to the dorsum of the hand. The skin incision lies between skin that is supplied by cutaneous branches of the ulnar nerve and skin that is supplied by cutaneous branches of the radial nerve. Damage to cutaneous nerves commonly occurs if the dissection of the flaps is begun within the fat layer. If the skin incision is taken down to the extensor retinaculum before the ulnar and radial flaps are elevated, the nerves are protected by the full thickness of the fat. Take care, however, to identify and preserve any nerve branches that are encountered during the incision of the subcutaneous tissue (Fig. 5-11). The area overlying the second extensor compartment is the commonest site for the nerve to be found.

Cutting a cutaneous nerve may result in a painful neuroma, but the resultant sensory defect rarely is significant.

Vessels

The radial artery crosses the wrist joint on its lateral aspect. As long as the dissection at the level of the wrist joint remains below the periosteum, the artery is difficult to damage.

 

How to Enlarge the Approach

 

Because it does not make use of an internervous plane, the incision cannot be extended proximally to expose the rest of the radius. It can be extended to expose the distal half of the dorsal aspect of the radius, however, by retracting the abductor pollicis longus and extensor pollicis brevis muscles, which cross the operative field obliquely.

To expose the entire dorsal surface of the metacarpals, extend the incision distally and retract the extensor tendons. (This type of extension seldom is required in practice.) The approach provides excellent exposure of the wrist joint and allows easy access to all six compartments of the extensor tunnel.

 

 

Figure 5-11 The dorsal aspect of the wrist and hand. Cross section of the distal forearm (inset). Note the compartmentalization of tendons into six distinct tunnels at the dorsal aspect of the distal forearm.

Applied Surgical Anatomy of the Dorsal Approach to the Wrist

 

 

Overview

 

Twelve tendons cross the dorsal aspect of the wrist joint and pass beneath the extensor retinaculum, which is a thickening of the deep fascia of the forearm. The extensor retinaculum prevents the tendons from “bowstringing.” Fibrous septa pass from the deep surface of the retinaculum to the bones of the forearm, dividing the extensor tunnel into six compartments. These septa must be separated from the retinaculum so that each compartment can be opened in surgery (see Fig. 5-11).

 

Landmarks and Incision

Landmarks

Two bony landmarks lie on the dorsal aspect of the wrist. The styloid process is the distal end of the lateral side of the radius. It also is the site of attachment of the tendon of the brachioradialis muscle. Its medial part articulates with the scaphoid bone (see Fig. 5-14A). Strong and sudden radial deviation of the wrist may cause the radial styloid process to slam into the scaphoid and fracture it (see Fig. 5-14B). Alternatively, such a force may cause a fracture of the radial styloid.

The styloid process often is excised when the scaphoid fails to unite or after arthritic changes in the wrist joint have affected the radial margin of the radioscaphoid joint. This procedure may be carried out in conjunction with a scaphocapitolunate arthrodesis.8

Lister tubercle (the dorsoradial tubercle) is a small bony prominence on the dorsum of the radius. The tendon of the extensor pollicis longus muscle angles around its distal end, changing direction about 45 degrees as it does so. When the wrist is hyperextended, the base of the third metacarpal comes very close to Lister tubercle, and the two bones can crush the trapped tendon of the extensor pollicis longus. This probably is the reason the tendon suffers delayed rupture in some cases of minimal or undisplaced fractures of the distal radius; the tendon sustains a vascular insult at the time of the original injury, even though it remains intact (see Fig. 5-14C).6

Incision

Longitudinal incisions crossing the lines of cleavage of the skin almost perpendicularly on the dorsum of the wrist can cause broad scarring. Nevertheless, because the skin on the wrist is so loose, this is one of those rare occasions when a skin incision can cross a major skin crease at right angles without causing a joint contracture.

 

Superficial and Deep Surgical Dissection

 

The extensor retinaculum is a narrow (2-cm) fibrous band that lies obliquely across the dorsal aspect of the wrist. Its radial side is attached to the anterolateral border of the radius; its ulnar border is attached to the pisiform and triquetral bones. (Were it attached to both bones of the forearm instead, pronation and supination would be impossible, because its fibrous tissue is incapable of stretching the necessary 30%.)

Fibrous septa pass from the deep surface of the extensor retinaculum to the bones of the carpus, dividing the extensor tunnel into six compartments (Fig. 5-12). From the radial (lateral) to the ulnar (medial) aspect, the compartments contain the following:

 

 

 

Figure 5-12 Anatomy of the distal forearm, with the extensor retinaculum excised and the septa remaining. The retinaculum on the ulnar side inserts into the

triquetrum and pisi form bones.

 

1. Abductor pollicis longus and extensor pollicis brevis. These tendons lie over the lateral aspect of the radius. They may become trapped or inflamed beneath the extensor retinaculum in their fibroosseous canal, producing de Quervain disease (tenosynovitis stenosans). Access to this compartment is required to apply plates to the radial column of the wrist joint.

2. Extensor carpi radialis longus and extensor carpi radialis brevis. These muscles run on the radial side of Lister tubercle before reaching the dorsum of the hand. The tendon of the extensor carpi radialis longus is used frequently in tendon transfers. The tendons run in separate synovial sheaths.

3. Extensor pollicis longus. This tendon passes into the dorsum of the hand on the ulnar side of Lister tubercle. It may rupture in association with fractures or rheumatoid arthritis. The oblique passage of this tendon on the dorsal aspect of the wrist creates significant problems for plate fixation of fractures of the distal radius. Tendon irritation and even rupture may occur due to abrasion of the tendon on the surface of the plate. Similar problems apply to a lesser degree with all the other extensor tendons.9

4. Extensor digitorum communis and extensor indicis. The indicis tendon is used commonly in tendon transfers.

5. Extensor digiti minimi. This tendon overlies the distal radioulnar joint.

6. Extensor carpi ulnaris. This tendon passes near the base of the ulnar styloid process. It is used sometimes in tendon transfers (Fig. 5-13; see Fig. 5-12).

    

    

   Figure 5-13 The extensor tendons have been removed, revealing the dorsal radiocarpal ligament. The radial artery is seen piercing the first dorsal interosseous muscle and contributing to the dorsal carpal rete. Note the hood mechanism for the index finger; contributions are made to it by the first dorsal interosseous and the first lumbrical muscles.

    

    

   Figure 5-14 A: Dorsal aspect of the bones of the distal forearm, wrist, and proximal hand. B: A strong and sudden radial deviation of the wrist may cause the radial styloid process to impinge on the scaphoid tubercle and fracture it. C: With sudden extreme dorsiflexion of the wrist, as when one falls on an outstretched hand, the extensor pollicis longus tendon may be trapped or crushed between the dorsal radial tubercle (Lister tubercle) and the base of the third metacarpal.

   Volar Approach to the Distal Radius

   The volar approach to the distal radius provides excellent exposure of the volar aspect of the distal radius. Its use is almost exclusively in the treatment of distal radial fractures and its popularity has increased greatly in recent years since the advent of locking plates.

   Other uses include the following:

   1. Bone grafting for nonunions of the distal radius

   2. Osteotomies of the distal radius

   3. Excision of the radial styloid or release of the brachioradialis

The approach is very similar to the lower end of the anterior approach to the radial shaft (page 148) but it utilizes the plane between the radial artery and the flexor carpi radialis and not the plane between the radial artery and brachioradialis. The exposure of the distal radius is therefore more ulnarward and retraction of the radial artery is not required to access the more central portions of the distal radius and wrist joint.

 

Position of the Patient

 

Place the patient supine on an operating table. Rest the forearm on a hand table in the supinated position so that the palm faces upward. Use an exsanguinating bandage (Fig. 5-15).

 

Landmarks and Incision

Landmarks

Palpate the styloid process of the radius. It is the most distal part of the lateral side of the radius. Then move in an ulna direction to palpate the tendon of flexor carpi radialis which is thick and immobile. The flexor carpi radialis muscle and tendon lie radial to the palmaris longus muscle at the level of the wrist and just to the ulnar side of the radial pulse.

Incision

Make a longitudinal incision overlying the tendon of flexor carpi radialis. Begin just above the skin crease of the wrist and extend the incision up the volar aspect of the forearm. The length of the incision will depend on the nature of the fracture pathology and the length of the plate to be used for fixation—7 cm is usually sufficient (Fig. 5-16).

Internervous Plane

 

The plane lies between the flexor carpi radialis supplied by the median nerve and the brachioradialis muscle supplied by the radial nerve.

 

Superficial Surgical Dissection

 

Incise the subcutaneous fat in the line of the skin incision. Incise the deep fascia overlying the tendon of flexor carpi radialis (Fig. 5-17). Identify the radial artery radially and the tendon of flexor carpi radialis ulnarly. Develop a plane between these two structures to expose the fascia overlying the pronator quadratus muscle (Figs. 5-18 and 5-19).

 

 

 

Figure 5-15 Position of the patient for volar approaches to the distal radius.

 

 

Figure 5-16 Incision for volar approach to wrist. The 5- to 7-cm incision overlies the tendon of flexor carpi radialis and ends just above the wrist joint crease.

 

 

 

Figure 5-17 The fascia over the tendon of flexor carpi radialis is incised and the radial artery is identified in the radial edge of the wound.

 

 

 

Figure 5-18 The tendon of flexor carpi radialis is retraced ulnarly to reveal the pronator quadratus muscle.

 

 

Figure 5-19 The pronator quadratus muscle is divided to expose the underlying volar aspect of the distal radius.

 

 

 

Figure 5-20 The pronator quadratus muscle is divided in the line of the skin incision to reveal the volar aspect of the distal radius.

 

Deep Surgical Dissection

 

The volar aspect of the distal radius is covered by the pronator quadratus muscle. Several techniques can be used to reach the bone of which three will be described. No technique has been proven to give better long-term function although minimally invasive techniques may give a slightly faster return to function.10,11

1. Complete muscle detachment

   Identify the insertion of the muscle into the anterolateral border of the radius beginning just below the radial styloid process. Detach this insertion by sharp dissection. Similarly detach the insertion of the muscle to the anterior surface of the distal end of the radius raising up a triangular flap of muscle. This technique gives the opportunity to close the muscle flap after surgery protecting the more superficial flexor muscles from an anteriorly applied plate.

2. Minimally invasive technique

   Identify the insertion of the muscle into the anterior surface of the distal end of the radius and detach it from the bone by sharp dissection. Leaving the lateral insertion intact tunnel underneath the muscle to expose the anterior surface of the bone. This technique is more soft tissue friendly but gives less exposure of the fracture site. Screws have to be inserted through stab incisions in the muscle.

3. Classical technique

Divide the pronator quadratus muscle in the line of the skin incision and elevate it from the anterior surface of the bone. This technique is more destructive and may be associated with slower initial recovery. Repair of the muscle is usually not possible (Fig. 5-20).

 

 

Dang

 

 

Vessels

The radial artery lies close to the lateral border of the wound and can be incised accidentally at any time during the dissection. Therefore, take care to identify and protect the artery. It is surrounded by venae comitantes and these may be easier to identify than the artery if an exsanguinating

tourniquet is used.

Nerves

The median nerve lies on the ulnar side of the approach and is protected as long as one stays radial to the flexor carpi radialis. If one strays ulnarward or do not use the pronator quadratus and its subperiosteal reflection to protect the structures on the ulnar side of the wrist, then the median nerve will be encountered and may be at risk of damage.

 

How to Enlarge the Approach

 

The incision can be extended usefully proximally and distally. Proximally, extend the skin incision along the line of the flexor carpi radialis muscle. Identify the proximal border of the pronator quadratus muscle following the internervous plane between median nerve innervated structures and radial nerve innervated structures (flexor carpi radialis and brachioradialis respectively). The exposure can also be extended distally by incising the wrist capsule and following the line of the flexor carpi radialis tendon. The tubercle of scaphoid is palpated in the distal most aspect of the incision and the wrist joint can be opened with visualization of the articular surface of the scaphoid. (See Volar Approach to the Scaphoid, page 50.)

 

Volar Approach to the Carpal Tunnel and Wrist

 

 

Decompression of the median nerve within the carpal tunnel is one of the most common operations of the hand. Two anatomic structures, the motor and palmar cutaneous branches of the median nerve, determine how the tunnel is approached. Both structures vary considerably in the paths they take; they are so unpredictable that “blind” procedures, which are acceptable elsewhere, must be avoided. If treated by open surgery the tunnel must be decompressed through a full incision and under direct vision. The uses of the incision include the following:

1. Decompression of the median nerve12,13

2. Synovectomy of the flexor tendons of the wrist

3. Excision of tumors within the carpal tunnel

4. Repair of lacerations of nerves or tendons within the tunnel

5. Drainage of sepsis tracking up from the midpalmar space

6. Open reduction and internal fixation of certain fractures and dislocations of the distal radius and carpus, including volar lip fractures of the radius and transscaphoid perilunate dislocations

 

Position of the Patient

 

Place the patient supine on an operating table. Rest the forearm on a hand table in the supinated position so that the palm faces upward. Use an exsanguinating bandage (see Fig. 5-15).

 

Landmarks and Incision

Landmarks

The thenar crease runs around the base of the thenar eminence. The proximal transverse skin crease of the wrist overlies the wrist joint. The tendon of the palmaris longus muscle bisects the anterior aspect of the wrist. Its distal end bisects the anterior surface of the carpal tunnel. It is easy to palpate in the distal forearm if the patient is instructed to pinch the fingers together and flex the wrist.

Incision

Begin the incision just to the ulnar side of the thenar crease, about one-third of the way into the hand. Curve it proximally, remaining just to the ulnar side of the thenar crease, until the flexion crease of the wrist is almost reached: To avoid problems in skin healing, do not wander into the thenar crease itself. Then, curve the incision toward the ulnar side of the forearm so that the flexion crease is not crossed transversely (Fig. 5-21).

 

Internervous Plane

 

There is no internervous plane. The approach is a true anatomic dissection in which the major nerves are identified, dissected out, and preserved. No muscles are transected except, on occasion, some fibers of the abductor pollicis brevis and palmaris brevis that cross the midline.

 

Superficial Surgical Dissection

 

Carefully incise the skin flaps. Remember that the palmar cutaneous branch of the median nerve, which usually presents on the ulnar side of the flexor carpi radialis, has a variable course. Dissection should be carried out

meticulously, with particular attention paid to the location of the nerve (see Fig. 5-21). After the fat is incised, the fibers of the superficial palmar fascia come into view; divide them in line with the incision.

Retract the curved flaps medially, exposing the insertion of the palmaris longus muscle into the flexor retinaculum (the transverse carpal ligament; Fig. 5-22). Retract the tendon toward the ulna and identify the median nerve between the tendons of the palmaris longus muscle and the flexor carpi radialis muscle. The nerve lies closer to the palmaris longus than to the flexor carpi radialis (Fig. 5-23).

Pass a blunt, flat instrument (such as a McDonald dissector) down the carpal tunnel between the flexor retinaculum and the median nerve (Fig. 5-24). Carefully incise the retinaculum, cutting down on the dissector to protect the nerve. Make the incision on the ulnar side of the nerve to avoid possible damage to its motor branch to the thenar muscle. Divide the entire length of the retinaculum (Fig. 5-25).

 

Deep Surgical Dissection

 

Identify the motor branch of the median nerve. It usually arises from the anterolateral side of the median nerve just as the nerve emerges from the carpal tunnel. The motor branch then curves radially and upward to enter the thenar musculature between the abductor pollicis brevis and flexor pollicis brevis muscles. Sometimes, however, the motor branch arises within the tunnel and pierces the flexor retinaculum to reach the thenar musculature. In these rare cases, the motor nerve itself may have to be decompressed before the patient’s symptoms will be relieved fully (see Fig. 5-25).

 

 

Figure 5-21 The incision for the volar approach to the wrist. The incision should be made on the ulnar side of the palmaris longus tendon to protect the palmar cutaneous branch of the median nerve.

 

 

Figure 5-22 The skin is retracted, and the deep fascia and tendon of the palmaris longus are inspected.

 

 

Figure 5-23 The deep fascia is incised. The palmaris longus is retracted toward the ulna, revealing the median nerve as it enters the carpal tunnel.

 

 

Figure 5-24 A spatula is placed under the transverse carpal ligament to protect the median nerve as the ligament is incised.

 

 

Figure 5-25 The transverse carpal ligament is released on the ulnar side of the nerve to avoid damage to the motor branch of the thenar muscle.

 

It rarely is necessary to gain access to the volar aspect of the wrist joint. If this is required, mobilize the median nerve in the carpal tunnel and retract it radially to avoid stretching its motor branch. Next, mobilize and retract the flexor tendons in the carpal tunnel (Fig. 5-26). Incising the base of the tunnel longitudinally exposes the volar aspect of the carpus. Extending the incision proximally provides access to the volar aspect of the wrist joint and the distal radius (Fig. 5-27). The most convenient approach for access to the volar aspect of the distal radius is the volar approach to the distal radius or the distal portion of the anterior approach to the radius (see Chapter 4).

 

 

Dang

 

 

Nerves

The palmar cutaneous branch of the median nerve arises 5 cm proximal to the wrist joint and runs down along the ulnar side of the tendon of the

flexor carpi radialis muscle before crossing the flexor retinaculum. The greatest threat to this nerve occurs if the skin incision is not angled to the ulnar side of the forearm (see Fig. 5-21).

The motor branch of the median nerve to the thenar muscles exhibits considerable anatomic variation. The risk to the nerve is minimized if the incision is made into the carpal tunnel on the ulnar side of the median nerve (see Applied Surgical Anatomy of the Volar Aspect of the Wrist and Fig. 5-39).

Vessels

The superficial palmar arch crosses the palm at the level of the distal end of the outstretched thumb. Blind slitting of the flexor retinaculum may damage this arterial arcade if the instrument passes too far distally. The arch is in no danger if the flexor retinaculum is cut carefully under direct observation for its entire length (see Figs. 5-21 and 5-39). Minimally invasive approaches to divide the flexor retinaculum rely on arthroscopic visualization of the anatomical structures to ensure their preservation.

 

How to Enlarge the Approach

Extensile Measures

 

Proximal Extension. The approach can be extended to expose the median nerve. To accomplish this, extend the skin incision proximally, running it up the middle of the anterior surface of the forearm (Fig. 5-28). Incise the deep fascia of the forearm between the palmaris longus and flexor carpi radialis muscles. Retract the flexor carpi radialis in a radial direction and the palmaris longus in an ulnar direction, exposing the muscle belly of the flexor digitorum superficialis muscle in the distal two-thirds of the forearm (Fig. 5-29). The median nerve adheres to the deep surface of the flexor digitorum superficialis, held there by fascia. Thus, if the flexor digitorum superficialis is reflected, the nerve goes with it (Fig. 5-30).

 

 

Figure 5-26 The median nerve is retracted radially and the flexor tendons are retracted toward the ulna, revealing the distal radius and joint capsule. An incision then is made into the capsule to expose the carpus.

 

 

Figure 5-27 Incise the joint capsule to expose the carpus.

 

 

 

Figure 5-28 Extend the wrist incision proximally to expose the distal forearm and median nerve.

 

 

Figure 5-29 Incise the fascia on the forearm between the palmaris longus and the flexor carpi radialis to expose the tendons and muscles of the flexor digitorum superficialis.

 

 

 

Figure 5-30 Reflect the flexor digitorum superficialis and note that the median nerve moves with it, because it is attached to the muscle via the posterior fascia of the muscle.

 

Distal Extension. The skin incision can be extended into a volar zigzag approach for any of the fingers, providing complete exposure of all the palmar structures (see Volar Approach to the Flexor Tendons and Fig. 5-45).

Volar Approach to the Ulnar Nerve

The volar approach is used for exploration of the ulnar nerve at the wrist. It is used primarily to decompress the canal of Guyon in cases of ulnar nerve compression. It also permits exploration of the ulnar nerve in cases of trauma. The approach is freely extensile proximally, allowing exposure of the nerve all the way up the forearm.

 

Position of the Patient

 

Place the patient supine on the operating table. Rest the hand on a hand table in the supinated position, so that the palm faces upward. Use an exsanguinating soft bandage, then inflate a tourniquet (see Fig. 5-15).

 

Landmarks and Incision

Landmarks

The hypothenar eminence is a readily palpable group of muscles on the ulnar border of the hand. The proximal transverse skin crease of the wrist overlies the wrist joint.

Incision

Make a curved incision, following the radial border of the hypothenar eminence and crossing the wrist joint obliquely at about 60 degrees. Extend the incision onto the volar aspect of the distal forearm. The incision should be about 5 to 6 cm long (Fig. 5-31).

 

Internervous Plane

 

There is no internervous plane. The approach is a true anatomic dissection in which the nerve and vessels are dissected out and preserved.

 

Superficial Surgical Dissection

 

Deepen the incision in the line of the skin incision and identify the tendon of the flexor carpi ulnaris in the proximal end of the wound (Fig. 5-32). Take care to identify and preserve the palmar cutaneous branch of the ulnar nerve which lies close to the plane of dissection in most patients. Mobilize the tendon by incising the fascia on its radial border, and retract the muscle and tendon in an ulnar direction to reveal the ulnar nerve and

artery (Fig. 5-33).

 

 

 

Figure 5-31 Incision for the exposure of the ulnar nerve in the canal of Guyon.

 

 

Figure 5-32 The volar carpal ligament is seen as a continuation of the deep palmar fascia and fibers of the flexor carpi ulnaris.

 

 

Figure 5-33 The volar carpal ligament is isolated and the nerve is protected in preparation for sectioning of the volar carpal ligament.

 

Deep Surgical Dissection

 

Trace the nerve and artery distally, incising overlying fibrous tissue, the volar carpal ligament. During this procedure, take great care to protect the nerve and vessel. The ulnar nerve now is exposed across the wrist joint; the canal of Guyon is decompressed (Fig. 5-34).

 

 

Dang

 

 

Nerves

The ulnar nerve is vulnerable during two phases of the dissection:

1. When the fascia on the radial side of the flexor carpi ulnaris is incised to allow retraction of the muscle, during superficial surgical dissection

2. When the volar carpal ligament is incised, during deep surgical dissection

If care is taken during these two phases of the procedure, the nerve should be safe.

 

How to Enlarge the Approach

Extensile Measures

 

Proximal Extension. Extend the skin incision proximally on the anterior aspect of the forearm, running it longitudinally up the middle of the forearm (Fig. 5-35). Incise the deep fascia in line with the incision and identify the radial border of the flexor carpi ulnaris. Develop a plane between the flexor carpi ulnaris muscle (which is supplied by the ulnar nerve) and the flexor digitorum superficialis muscle (which is supplied by the median nerve), retracting the flexor carpi ulnaris toward the ulna to reveal the ulnar nerve. This incision can expose the ulnar nerve almost to the level of the elbow joint (Fig. 5-36), where it passes between the two heads of the flexor carpi ulnaris muscle. If the nerve is exposed for a long distance, take care to preserve as many small vessels attaching to it as possible.

 

 

 

Figure 5-34 The roof of the canal has been incised, revealing the ulnar nerve and artery.

 

 

 

Figure 5-35 Explore the ulnar nerve proximally in the forearm.

 

 

 

Figure 5-36 Develop the plane between the flexor carpi ulnaris and the flexor digitorum superficialis. In the depth of the wound, the ulnar nerve is visualized running under the flexor carpi ulnaris.

 

Applied Surgical Anatomy of the Volar Aspect of the Wrist

 

 

 

Overview

 

The carpal tunnel is a fibroosseous canal on the volar surface of the carpus. Its base is formed by the deeply concave surface of the volar aspect of the carpal bones, and its roof is formed by the flexor retinaculum (Fig. 5-37). The ulnar nerve runs over the surface of the flexor retinaculum; it is enclosed in its own fibroosseous canal, the canal of Guyon (Fig. 5-38).

 

Landmarks and Incision

 

The four attachments of the flexor retinaculum all are palpable (Figs. 5-42 and 5-43A):

1. The pisiform. This is located on the ulnar border of the wrist. The pisiform is a mobile sesamoid bone lying within the tendon of the flexor carpi ulnaris muscle. The bone was sometimes used by artisans to tap nails into soft wood or leather. Historically stress fractures were noted in cobblers who used to use the pisiform for this purpose. Acute fractures have been described in contact sports athletes14,15 and pisotriquetral arthrosis may be a cause of ulnar wrist pain.16

2. The hook of the hamate. This is slightly distal and radial to the pisiform. To locate it, place the interphalangeal joint of the thumb on the pisiform, pointing the tip toward the web space between the thumb and the index finger, and rest the tip of the thumb on the palm. The hook of the hamate lies directly under the thumb. Because it is buried under layers of soft tissue, one must press firmly to find its rather shallow contours. The deep branch of the ulnar nerve lies on the hook, and neurapraxia of the nerve has been described in cases of fracture.17

3. The ridge of the trapezium. The trapezium lies on the radial side of the carpus where it articulates with the first metacarpal. To palpate the ridge, identify the joint between the trapezium and the thumb’s metacarpal bone by moving the joint passively. The ridge feels like a prominent lump on the volar aspect of the trapezium (see Fig. 5-43A).

4. The tubercle of the scaphoid. This small protuberance is barely palpable just distal to the distal end of the radius on the volar aspect of the wrist joint (see Figs. 5-42 and 5-43A).

On its radial side, the retinaculum also attaches across the groove on the trapezium, converting the groove into a tunnel through which the

tendon of the flexor carpi radialis muscle runs before it attaches to the base of the second and third metacarpals (see Figs. 5-42 and 5-43A).

 

 

 

Figure 5-37 Superficial anatomy of the wrist and palm. Note the course of the cutaneous branch of the median nerve. The longitudinal bands of the palmar aponeurosis are continuations of the palmaris longus tendon.

 

Superficial Surgical Dissection and Its Dangers

 

Three structures run across the surface of the flexor retinaculum (see Fig. 5-37):

1. Tendon of the palmaris longus. The palmaris longus is a vestigial muscle of no functional importance. Its tendon is used frequently for tendon grafting. It is important to test for the presence of this tendon before surgery, because it is absent in about 10% of the population. The tendon also is used as an anatomic landmark for the injection of steroid into the

   carpal tunnel. If the patient is asked to flex the wrist against resistance while pinching his fingers together the tendon of the palmaris longus (if it is present) is easily palpable together with the thicker and more radially located tendon of the flexor carpi radialis. The easily defined gap between the two tendons is the site where the needle should be inserted for injection of the carpal tunnel. The needle should be inserted here dorsally and distally at an angle of almost 45 degrees. Note also that because the carpal tunnel is a distensible space, if problems are encountered in injecting it, then the tip of the needle either is still in the flexor retinaculum or is imbedded in one of the tendons in the tunnel.

   Fluid inserted through correctly positioned syringes should enter the space without encountering much resistance to pressure.

2. Palmar cutaneous branch of the median nerve. The course of the palmar cutaneous branch of the median nerve may vary in four important ways (see Fig. 5-37)18,19,20:

   1. Normally, the nerve branches off 5 cm proximal to the wrist. It runs along the ulnar side of the tendon of the flexor carpi radialis before crossing the flexor retinaculum. On rare occasions, the nerve actually may be enclosed by parts of the flexor retinaculum and, thus, may run in a tunnel of its own on the wrist.

       

       

      Figure 5-38 The palmar aponeurosis and fascia have been elevated to reveal the transverse carpal ligament. The fascia of the forearm and the expansions of the flexor carpi ulnaris (volar carpal ligament) are left intact where they form the roof of the tunnel of Guyon. The canal of Guyon looking from proximal to distal (inset). The transverse carpal ligament forms the floor of the tunnel of Guyon; the roof is formed by the volar carpal ligament, which is a condensation of the fascia of the forearm and expansions of the flexor carpi ulnaris tendon. The canal is formed

      medially by the pisiform bone and laterally by the hook of the hamate bone.

       

       

       

      Figure 5-39 The palmar aponeurosis has been resected further distally to expose the superficial palmar arterial arch. The transverse carpal ligament also has been resected. The median nerve lies superficial to the tendons of the profundus, but at the same level with the superficialis muscle tendons. Note the motor branch of the median nerve to the thenar muscles. The location of its division from the median nerve is quite variable.

       

      The nerve divides into two major branches, medial and lateral, while crossing the flexor retinaculum. The lateral is the larger branch. Both supply the skin of the thenar eminence.

   2. Less often, the nerve arises from the median nerve in two distinct branches, which travel separately across the wrist.21

   3. The palmar cutaneous branch may arise within the carpal tunnel and

      penetrate the flexor retinaculum to supply the skin of the thenar eminence.

   4. The palmar cutaneous branch may be absent, replaced by a branch derived from the radial nerve, the musculocutaneous nerve, or the ulnar nerve.21

      The skin incision described above avoids cutting the nerve by angling across the distal forearm in an ulnar direction. One must be aware, however, that considerable variability exists in the course of the nerve. Because damage can result in the formation of a painful neuroma, transverse incisions on the volar aspect of the distal forearm must be avoided. (Compression lesions of the nerve have been reported, but these are rare.)22,23

3. Ulnar nerve and palmar cutaneous branch of ulnar nerve.24 The ulnar nerve runs down the volar surface of the distal forearm under cover of the flexor carpi ulnaris muscle (see Fig. 5-38). The ulnar artery lies on its radial side. The tendon of the flexor carpi ulnaris inserts into the pisiform, which then joins with the hamate and fifth metacarpal via ligaments. Just proximal to the wrist, the artery and nerve emerge from under the tendon to pass over the flexor retinaculum (the transverse carpal ligament) of the wrist (see Fig. 5-38).

 

 

Figure 5-40 The palmar aponeurosis has been elevated up to its attachment to the digital flexor sheaths. Its deeper attachments to the volar plate and bone have been cut. The flexor tendons and digital nerves are shown in continuity, as are the superficial palmar arch and the thenar and hypothenar muscles. Note that the digital nerves and vessels go deep or dorsal to the natatory ligaments.

 

Flexor Pollicis Brevis. Origin. The muscle’s superficial part arises from the distal edge of the flexor retinaculum and the tubercle of the trapezium, a bone in the wrist. It passes along the radial side of the tendon of the flexor pollicis longus. The deeper (and medial) portion of the muscle is very small, and arises from the ulnar side of the first metacarpal bone between the oblique part of the adductor pollicis and the lateral head of the first dorsal interosseous muscle. Insertion. The superficial head is inserted into the radial side of the base of the proximal phalanx of the thumb; in its

tendon of insertion there is a sesamoid bone. The deep head is inserted into the ulnar side of the base of the first phalanx with the adductor pollicis. Action. Flexor of the metacarpophalangeal joint of the thumb. Nerve supply. Superficial head—median nerve (motor or recurrent branch). Deep head—deep branch of ulnar nerve.

Abductor Pollicis Brevis. Origin. Flexor retinaculum and tubercle of scaphoid. Insertion. Radial side of base of proximal phalanx of thumb. Action. Abduction of thumb at metacarpophalangeal joint and rotation of proximal phalanx of thumb. Nerve supply. Median nerve (motor or recurrent branch).

 

 

 

Figure 5-41 Portions of the thenar and hypothenar muscles have been resected to reveal their layering. The ulnar nerve passes between the origin of the abductor digiti minimi and the flexor digiti minimi. In the thenar region, the course of the flexor pollicis longus is seen as it crosses between the two heads of the flexor

pollicis brevis. Portions of the long flexors of the fingers have been resected to show their layering. The superficial palmar arch runs superficial to the tendons, whereas the deep palmar arch is immediately deep to the tendons. Note that potential spaces develop on the undersurface of the flexor tendons and their sheaths, and on the deep intrinsic muscles of the hand, the interosseous on the hypothenar side and the adductor pollicis on the thenar side. A septum that runs from the undersurface of the flexor tendons to the third metacarpal divides the two spaces. More distally, the superficial transverse ligament has been resected, revealing the course of the lumbricals and the digital vessels that run superficial or palmar to the deep transverse metacarpal ligaments.

 

Adductor Pollicis. Origin. Oblique head from bases of second and third metacarpals, trapezoid, and capitate. Transverse head from palmar border of third metacarpal. Insertion. Ulnar side of base of proximal phalanx of thumb via ulnar sesamoid. Action. Adduction of thumb. Opposition of thumb. Nerve supply. Deep branch of ulnar nerve.

Opponens Pollicis. Origin. Flexor retinaculum. Insertion. Radial border of thumb metacarpal. Action. Opposition of metacarpal bone of thumb. Nerve supply. Median nerve (motor or recurrent branch).

 

 

Figure 5-42 The deepest layer of the palm is revealed. The deep palmar arterial arch lies deep to the long flexor tendons and superficial to the interosseous muscles. It crosses the palm with the deep branch (motor branch) of the ulnar nerve. The nerve supplies all the interosseous muscles. More distal, the interosseous muscles are seen running deep (dorsal) to the deep transverse ligament. The deep transverse metacarpal ligaments attach to the palmar plate, which is seen on the fifth metacarpal. The pulleys of the thumb are seen in relationship to the digital nerves.

 

 

 

Figure 5-43 A: The bones of the wrist and palm and the proximal metacarpals are seen in relationship to the creases of the wrist. The necks of the metacarpals are at the level of the distal palmar crease. The distal wrist crease runs from the proximal

portion of the pisiform to the proximal portion of the tubercle of the scaphoid and marks the proximal level of volar carpal ligament. The proximal transverse palmar crease is at the radiocarpal joint. B: Kaplan’s cardinal line. Used to locate the motor branch of the median nerve to the thenar muscles.

 

At this level, the anatomic arrangement of these structures can be remembered by the mnemonic “ANT”: The artery is the most lateral structure, then the nerve, and, finally, the tendon of the flexor carpi ulnaris (see Fig. 5-38).

The palmar cutaneous branch arises in the forearm. It travels lateral to the ulnar artery in 75% of patients. The nerve perforates the fascia of the anterior forearm just proximal to the distal wrist crease. In the palm, the nerve travels superficial to the superficial palmar arch in most cases. It is therefore at risk during decompression of the ulnar nerve in the Canal of Guyon.

At the wrist, the nerve is particularly vulnerable to damage by lacerations. The grim triad of lacerations of the tendon of the flexor carpi ulnaris, the ulnar artery, and the ulnar nerve is a common sequela of falling through a window with the ulnar border of the wrist flung forward to protect the face.

As the nerve crosses the flexor retinaculum, it is covered with a tough fibrous tissue that is continuous with the deep fascia of the forearm, the volar carpal ligament. The tunnel thus formed, the canal of Guyon, has four boundaries: A floor, the flexor retinaculum (transverse carpal ligament); a medial wall, the pisiform; a lateral wall, the hamate; and a roof, the volar carpal ligament (distal fascia of the forearm; see Fig. 5-38).

Around the pisiform, the ulnar nerve divides into two branches. The superficial branch supplies the palmaris brevis muscle and the skin of the small finger and ulnar half of the ring finger. The deep branch supplies all the small intrinsic muscles of the hand, except those of the thenar eminence and the radial two lumbricals (see Figs. 5-39 to 5-42).

 

Deep Surgical Dissection and Its Dangers

Median Nerve

The median nerve crosses the volar aspect of the distal forearm deep to the flexor digitorum superficialis muscle. Just above the wrist, it becomes superficial and lies between the tendons of the palmaris longus and flexor carpi radialis muscles. It enters the palm by traversing the carpal tunnel (see Fig. 5-38).

Within the tunnel, the nerve lies superficial to the tendons of the flexor digitorum profundus and flexor pollicis longus muscles. The superficialis tendons lie toward the ulnar side of the nerve. At the distal border of the flexor retinaculum, the nerve divides into two branches (see Figs. 5-39 and 5-40).

1. The medial branch sends cutaneous branches to the adjacent sides of the ring and middle fingers, and to the adjacent sides of the middle and index fingers.

2. The lateral branch sends cutaneous branches to the radial side of the index finger and to both sides of the thumb. The lateral branch usually also sends off the motor, or recurrent, nerve (see Fig. 5-39), which is the key surgical landmark and major surgical danger in carpal tunnel decompression.

The motor nerve supplies the muscles of the thenar eminence. Its course may take any one of eight significant variations22,25:

1. The classic course (seen in 50% of patients). The branch arises from the volar radial aspect of the median nerve distal to the radial end of the carpal tunnel. The nerve hooks radially and upward to enter the thenar muscle group between the flexor pollicis brevis and abductor pollicis brevis muscles.

2. The position of the motor branch can be estimated by drawing one vertical line from the web space between the middle and index fingers, drawing another from the radial origin of the first web space, then connecting to the hook of the hamate (Kaplan’s cardinal line). The intersection of these two lines marks the entrance of the motor branch into the thenar muscles (see Fig. 5-43B).26

3. A variation that occurs in about 30% of patients. The branch arises from the anterior surface of the nerve within the carpal tunnel. It passes through the tunnel with its parent nerve and hooks around the distal end of the flexor retinaculum to enter the thenar group between the flexor pollicis brevis and abductor pollicis brevis muscles.

4. A variation that occurs in about 20% of patients. The branch arises from the anterior surface of the nerve within the carpal tunnel. It travels radially to pierce the flexor retinaculum and enter the thenar group of muscles between the abductor pollicis brevis and flexor pollicis brevis muscles.27

5. A rare variation. The branch arises from the ulnar side of the median

   nerve.28 It crosses the median nerve within the tunnel, then hooks around the distal end of the flexor retinaculum to enter the thenar muscle group. It also may pass through the flexor retinaculum and lie anterior to it.29

6. Another rare variation. The nerve arises from the anterior surface of the median nerve within the carpal tunnel. At the distal end of the flexor retinaculum, the branch hooks radially over the top of the retinaculum. The nerve crosses the distal part of the retinaculum almost transversely before entering the thenar group of muscles.

7. A very rare variation (multiple motor branches).30 Double nerves may follow any of the courses described above.

8. A third rare variation (high division of the median nerve).31 The nerve may divide into medial and lateral branches high up in the forearm. The thenar branch, originating from the lateral branch, may leave the carpal tunnel either in the conventional manner or by piercing the flexor retinaculum on its radial side.

All these variations should be considered when the nerve is exposed. If the tunnel is opened on the ulnar side of the nerve, the motor branch will be preserved unless it lies on the same side. Patients with exceptionally rare variations usually have large palmaris brevis muscles, which should alert the surgeon to the possibility during the approach.22

Flexor Digitorum Superficialis

Within the carpal tunnel, the tendons to the middle and ring fingers are superficial to the tendons of the index and little fingers. This arrangement dictates correct repair in cases of multiple tendon laceration (see Figs. 5-38 and 5-41).

Flexor Digitorum Profundus

The tendons of the flexor digitorum profundus lie deep to the tendons of the flexor digitorum superficialis. The tendon to the index finger is separate; the other three still may be attached partially to each other as they pass through the carpal tunnel (see Fig. 5-41).

Flexor Pollicis Longus

The tendon of the flexor pollicis longus lies deep to that of the flexor carpi radialis and is found on the most radial aspect of the canal at the same depth as the profundus tendons (see Fig. 5-41).

Flexor Carpi Radialis

The flexor carpi radialis tendon perforates the flexor retinaculum to lie in the groove of the trapezium before it inserts into the bases of the second and third metacarpals. It does not pass through the carpal tunnel (see Fig. 5-42).

 

Volar Approach to the Flexor Tendons

The volar approach provides the best possible exposure of the flexor tendons within their fibrous sheaths.32 It also provides excellent exposure of both neurovascular bundles in the finger. The skin incision can be extended into the palm, the volar surface of the wrist, and the anterior surface of the forearm, making it a suitable approach in cases of trauma, where many levels may have to be exposed. Its other major advantage is that many skin lacerations can be incorporated into the skin incision. Its uses include the following:

1. Exploration and repair of flexor tendons

2. Exploration and repair of digital nerves and vessels

3. Exposure of the fibrous flexor sheath for drainage of pus

4. Excision of tumors within the fibrous flexor sheath

5. Excision of palmar fascia in Dupuytren contracture

 

Position of the Patient

 

Place the patient supine on the operating table with the arm abducted and lying on an arm board. Adjust the height of the table to make sitting comfortable. Most right-handed surgeons prefer to sit on the ulnar side of the affected arm. An exsanguinating bandage and tourniquet, as well as good lighting, are essential (see Fig. 5-15).

 

Landmarks and Incision

Landmarks

Three major skin creases traverse the fingers: The distal phalangeal crease, just proximal to the distal interphalangeal joint; the proximal phalangeal crease, just proximal to the proximal interphalangeal joint; and the palmar digital crease, well distal to the metacarpophalangeal joint. The course of the volar zigzag incision takes these creases into account, running diagonally across the finger between creases (Fig. 5-44).

Incision

Before the fingers are incised, mark the skin with methylene blue to outline the proposed site. The angles of the zigzag should be about 90 degrees to each other (or to the transverse skin crease); angles considerably less than 90 degrees to each other may lead to necrosis of the corners (Fig. 5-45A). The angles should not be placed too far in a dorsal direction; otherwise, the neuromuscular bundle may be damaged when the skin flaps are mobilized (see Fig. 5-45B). Of course, the basic zigzag pattern should be modified to accommodate any pre-existing lacerations (Fig. 5-46).

 

 

 

Figure 5-44 The relationship of the skin creases to the tendons and joints of the wrist and hand is seen.

 

 

Figure 5-45 A: Basic zigzag incision for exposure of the flexor tendons of the palm and fingers. B: If an incision is placed too far laterally or medially, the neurovascular bundle may be damaged.

 

 

 

Figure 5-46 The basic zigzag pattern should be adapted to pre-existing lacerations for exploration of the underlying structures. When adapting the skin incisions to previously existing lacerations, attempt to maintain an angle of about 90 degrees to prevent necrosis of the corners of the incision (inset).

 

Internervous Plane

There is no true internervous plane. The skin at the site of the incision is innervated by nerves coming from either side of the incision, so no areas of anesthesia are created.

 

Superficial Surgical Dissection

 

Reflect the skin flaps carefully with a skin hook, starting at the apex. Elevate the flaps along with some underlying fat. Do not mobilize the flaps widely until the level of the flexor sheath is reached, to ensure thick flaps and reduce the risk of skin flap necrosis (Fig. 5-47).

 

Deep Surgical Dissection

 

To expose the flexor tendons, carefully incise the subcutaneous tissues along the midline in a longitudinal fashion (Fig. 5-48). The flexor tendons lie directly underneath, within their fibrous flexor sheaths.

To expose the digital nerve and vessel, gently separate the subcutaneous tissues at the lateral border of the fibrous flexor sheath. The neurovascular bundle is separated from the volar subcutaneous flap by a thin layer of fibrous tissue known as Grayson ligament. This layer must be opened for full exposure of the neurovascular bundle. The easiest way to pry the tissues apart is to open gently a small pair of closed scissors so that the blades separate the tissues in a longitudinal plane. The blades actually are working along the line of the digital nerve, maximizing exposure of the nerve while minimizing the chance of accidental laceration (Fig. 5-49; see Fig. 5-47).

Although the approach can be deepened to expose the bone this extension is not recommended for the treatment of most bony injuries. Surgery on the osseous structures is usually safer through a midlateral or dorsal incision (Fig. 5-50). The exceptions are the repair of the volar plate of the proximal interphalangeal joint and the treatment of some fracture dislocations of the proximal interphalangeal joint. To approach the volar surface of the joint, divide the C1, A3, and C2 pulleys. Gently retract the flexor tendons using a vascular loop taking care to preserve the vinculae. The volar plate is now exposed. Ensure that the divided pulleys are reconstructed during closure (Fig. 5-51).

Incising the fibrous flexor sheath, retracting the tendons, and incising the periosteum from the volar surface of the bone lead to adhesions within the fibrous flexor sheath. It is very important to note that the consequences of this will be the loss of full function of the finger. Therefore, every effort

should be made to avoid this at all costs.

 

 

 

Figure 5-47 Elevate thick skin flaps. Stay as close to the sheath as possible to prevent damage to the laterally placed neurovascular structures.

 

 

Figure 5-48 Expose the flexor tendons in a longitudinal fashion. The digital nerves lie lateral to the tendons. Maintain the A2 and A4 pulleys.

 

 

 

Figure 5-49 Identify the neurovascular bundles and preserve them.

 

 

 

Figure 5-50 A: Incision for the midlateral approach to the finger. The incision lies between the proper digital nerve, which runs toward the palm, and its dorsal branch. The incision also can be made with the finger flexed; connect the dorsal portions of the interphalangeal creases (inset). B: Lateral view of the anatomy of the finger. Note the division of the proper (common) digital nerve into dorsal and palmar branches, the relationship of the palmar division of the nerve to the flexor tendon sheath, and the insertion of the lumbrical and interossei muscles into the hood mechanism.

 

 

Dang

 

 

Digital nerves and vessels can be damaged if the skin mobilization extends too far in a dorsal direction.

Skin flaps should not be cut at too acute an angle, and skin sutures should be meticulous to ensure closure. Skin flaps should be thick enough to avoid skin necrosis (see Fig. 5-46). The tourniquet should be removed and hemostasis secured before closure is undertaken.

 

How to Enlarge the Approach

Proximal Extension

The zigzag skin incision can be extended onto the palm, eventually joining the curved incision parallel to the thenar crease that is used for exposure of the structures of the palm, volar surface of the wrist, and anterior surface of the forearm. The key to making these incisions is to avoid crossing flexion creases at 90 degrees, thus preventing the development of flexion contractures, and to leave skin flaps with substantial corners (see Fig. 5-46).

 

 

 

Figure 5-51 The C1, A3, and C2 pulleys have been divided to allow retraction of the flexor tendons and exposure of the volar plate.

Midlateral Approach to the Flexor Sheaths, Proximal and Middle Phalanges

 

 

The midlateral approach is a popular way of reaching the flexor tendons and digital nerves in the fingers. It affords access to the neurovascular bundle on the incised side of the finger; at the same time, it is difficult to extend into the palm. Its uses include the following:

1. Open reduction and stabilization of phalangeal fractures

2. Exposure of the fibrous flexor sheath and its contents

3. Exposure of the neurovascular bundle

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm stretched out on an arm board. Good lighting and a good exsanguinating bandage and tourniquet are essential (see Fig. 5-15).

 

Landmarks and Incision

Landmarks

The proximal and distal interphalangeal creases are the key to this skin incision. They extend around the medial and lateral surfaces of the fingers and end slightly nearer the dorsal than the volar surface of the finger.

The creases may disappear if the finger is very swollen or if it is struck in full extension. If so, the surgical landmark for the skin incision is the junction between the wrinkled dorsal and the smooth volar skin on the side of the finger (see Fig. 5-50).

Incision

Make a longitudinal incision on the lateral aspect of the finger, starting at the most dorsal point of the proximal finger crease. Continue cutting distally to the distal interphalangeal joint, passing just dorsal to the dorsal end of the flexor skin crease. Extend the incision farther distally toward the lateral end of the fingernail. The incision actually is dorsolateral rather than truly lateral (see Fig. 5-50). Alternatively, flex the finger and make an incision connecting dorsal end points of the interphalangeal crease.

 

Internervous Plane

There is no true internervous plane, because no intermuscular interval is developed. The nerve supply to the finger comes mainly from two sources, the dorsal digital nerves and the volar, or palmar, digital nerves. Because the skin incision marks the division between these two supplies, it causes no significant areas of hypoesthesia.

 

 

 

Figure 5-52 Develop the skin flap down to the flexor sheath, maintaining the neurovascular bundle in the volar flap.

 

Superficial Surgical Dissection

 

Develop a volar skin flap by incising the subcutaneous flap in line with the skin incision. The fat over the proximal interphalangeal joint is quite thin; take care not to incise the joint itself. Continue the dissection toward the midline of the finger, angling slightly in a volar direction. The main neuromuscular bundles lie in the volar flap (Fig. 5-52).

 

Deep Surgical Dissection

 

If the approach is being used for tendon exploration and repair incise the fibrous flexor sheath longitudinally to expose the underlying tendon (Fig. 5-53). Tendon damage is often associated with damage to the digital nerve and in such cases the neuromuscular bundles also can be dissected out from within the volar flap (Fig. 5-54).

If the approach is being used for bony surgery expose the periosteum of the phalanx just dorsal to the insertion of the flexor sheath. Develop an epiperiosteal plane dorsally lifting the extensor tendon off the bone. Try to preserve as much periosteum as possible. Avoid incision into the flexor sheath as bleeding around the flexor tendons may result in adhesions (Fig. 5-55).

 

 

Dang

 

Nerves

The palmar digital nerve is in danger if the skin incision and approach drift too far in a volar direction. This approach always should begin just dorsal to the end of the interphalangeal creases. If the approach does begin at this site, the danger to the palmar digital nerve will be diminished (see Fig. 5-50A).

Vessels

The volar digital artery runs with the digital nerve on its dorsal side. It also may be damaged if the approach moves too far in a volar direction (see Fig. 5-50).

 

How to Enlarge the Exposure

 

Continue the dissection around the fibrous sheath to expose the neurovascular bundle on the opposite side. Note that the exposure gained is not as good as that offered by a zigzag volar approach.

 

 

 

Figure 5-53 Incise the flexor sheath longitudinally to reveal the tendons.

 

 

 

Figure 5-54 By longitudinal dissection, the neurovascular structures are revealed within the volar flap.

 

 

Figure 5-55 To expose the dorsal surface of the bone develop an epiperiosteal plane to lift the extensor tendon from the bone.

 

Dorsal Approach to Phalanges and Interphalangeal Joints

 

 

The dorsal approach to the phalanges and interphalangeal joints is almost exclusively used for open reduction and internal fixation of fractures and fracture dislocations of these structures. Access to bone is much easier than through volar or lateral approaches because the only deep structure between skin and bone is the extensor mechanism.

 

Position of patient

 

Place the patient supine on the operating table, pronate the forearm and place the arm on an arm board. Exsanguinate the arm using a soft rubber

bandage and inflate a tourniquet (Fig. 5-1).

 

Landmarks and Incision

Landmarks

Passively flex the metacarpophalangeal, proximal and distal interphalangeal joints to identify their position.

Incisions

The choice of incision depends on the pathology to be treated.

 

Metacarpophalangeal Joint. Make a gently curved incision over the joint. The incision can be curved in either direction but as a rule a radially curved incision is preferred over the second metacarpophalangeal joint and a dorsoulnar curved incision over the fifth metacarpophalangeal joint.

 

Proximal Interphalangeal Joint. Two incisions are possible. The first is a straight incision directly over the joint; the second is a curved incision at the same site. The curve should avoid the radial border of the index finger and the ulnar border of the little finger. The straight incision avoids creation of a skin flap. The curved incision avoids scarring of the skin and tendon being in the same line.

 

Middle Phalanx. Make either a gently curved incision centered over the fracture or a straight incision at the same site. The position and length of the incision will depend on the pathology to be treated. The advantages and disadvantages of these incisions are the same as for the proximal phalangeal joint approach (see Fig. 5-56).

 

Internervous Plane

 

No internervous plane is available for use. Because the skin of the dorsum of the fingers receives sensory nerve supply from both radial and ulnar sides sensory denervation does not occur.

 

Superficial Surgical Dissection

 

Deepen the incision by blunt dissection taking care to avoid dividing longitudinal branches of dorsal veins. Retract and elevate skin and subcutaneous tissue as a single layer to expose the extensor mechanism.

 

 

Figure 5-56 Incisions for exposure of the metacarpophalangeal joints, the proximal interphalangeal joint, and the middle phalanx.

 

 

 

Figure 5-57 Metacarpophalangeal joint. To expose the joint either divide the extensor hood in the middle or on its ulna side and then divide the joint capsule longitudinally.

 

Deep Surgical Dissection

At the level of the metacarpophalangeal joint divide the tendon of extensor digitorum in the midline to reveal the metacarpophalangeal joint capsule and the distal end of the proximal phalanx. Alternatively, divide the extensor hood just on the ulnar side of the extensor digitorum tendon. With either approach divide the dorsal capsule of the joint longitudinally to enter the joint (Fig. 5-57).

At the level of the proximal phalangeal joint make a gently curved longitudinal incision between the central slip and the lateral band. Make a longitudinal incision into the joint capsule to enter the joint (Fig. 5-58).

At the level of the middle phalanx/distal interphalangeal joint make a longitudinal incision through both the terminal extensor tendon and its triangular ligament (Fig. 5-59).

 

 

 

Figure 5-58 Proximal interphalangeal joint. Make a curved longitudinal incision between the central slip and the lateral band entering the joint by dividing the joint capsule longitudinally.

 

 

Figure 5-59 Middle phalanx. Make a longitudinal incision through the center of the extensor tendon directly down onto bone.

 

 

Dang

 

 

If curved skin incisions are used take care not to undermine the skin. The flap that is mobilized should consist of skin and subcutaneous tissue to reduce the risk of flap necrosis.

 

How to Extend the Approach

 

These approaches cannot usefully be extended and are designed to treat specific local pathology.

 

Applied Surgical Anatomy of the Finger Flexor Tendons

 

 

This section describes only the anatomy of the finger flexor tendons. For a general description of the palmar anatomy, see Applied Surgical Anatomy of the Volar Aspect of the Wrist.

 

Overview

 

The anatomy of the finger flexor tendons provides the key to the treatment

and prognosis of flexor tendon injuries. Nowhere else in the body are the links between anatomy, pathology, and treatment illustrated so clearly. The structure of the tendons, their blood supply, and their special relationship to other structures all relate to the pathogenesis of injury and repair.

The anatomy of the finger flexor tendons encompasses zones, each of which is separated from the others by anatomic landmarks. The zones all must be treated differently in cases of tendon laceration. We shall consider the anatomy from the proximal to the distal aspect, from zone 5 to zone 1, as devised by Milford (Fig. 5-60).33

Zone 5

Zone 5 is in the anterior compartment of the forearm, proximal to the flexor retinaculum and the carpal tunnel (see Fig. 5-60). At that point, nine distinct tendons run into the hand toward the digits. Each finger has two tendons, one each from the flexor digitorum superficialis muscle and the flexor digitorum profundus muscle. The thumb has one long flexor, the flexor pollicis longus.

The tendons in zone 5 are not enclosed in a tight canal, but are surrounded by a synovial sheath in the distal part of the forearm. Tendon repairs carried out in this area generally are successful, and independent finger flexion usually returns.

Zone 4

Zone 4 encompasses the tendons as they run through the carpal tunnel. Eight tendons remain in a common synovial sheath throughout the carpal tunnel.

Tendon repairs carried out in zone 4 have a good prognosis, but not as good as the prognosis of those carried out in zone 5, because the tendons are enclosed in a fibroosseous tunnel. The tunnel must be opened for repairs, and adhesions may form after surgery.

Zone 3

Zone 3 is the zone of the lumbrical origin. As the flexor digitorum profundus tendons traverse the palm, a lumbrical muscle arises from each tendon. The radial two lumbricals arise from a single head, from the radial side of the profundus tendons to the index and middle fingers. The ulnar two lumbricals arise from two heads, from the adjacent sides of the profundus tendons between which they lie. The tendons of the lumbricals pass along the radial sides of the metacarpophalangeal joints before they insert into the dorsal expansion. They pass volar to the axes of the

metacarpophalangeal joints; thus, they act as flexors of those joints, even as they extend the interphalangeal joints (see Fig. 5-41).

 

 

 

Figure 5-60 The zones of the wrist and hand (according to Milford).

 

Lacerations in zone 3 almost invariably involve damage to the lumbrical muscles. Most surgeons do not recommend repairing the lumbricals; the increased tension on the muscles caused by the repair produces fixed flexion at the metacarpophalangeal joints and limited flexion at the interphalangeal joints, resulting in an intrinsic plus hand.

Zone 2

Zone 2 stretches from the distal palmar crease to the middle of the middle phalanx. In this area, the two tendons for each finger run together in a common fibroosseous sheath.

The sheaths run from the level of the metacarpal heads (the distal palmar crease) to the distal phalanges. They are attached to the underlying bone and prevent the tendons from bowstringing.

Thickenings in the fibrous flexor sheath are constant (Fig. 5-61). They act as pulleys, directing the sliding movement of the tendons. There are two types: Annular and cruciate. Annular pulleys are composed of a single

fibrous band (ring); cruciate pulleys have two crossing fibrous strands (cross). Annular pulleys act much like the rings on a fishing rod. Without the ring, the fishing line would pull away from the rod as it bends. This effect is known as bowstringing; in human terms, it results in the loss of range of movement and power in the affected finger. Annular pulleys include the following:

1. The A1 pulley, which overlies the metacarpophalangeal joint. It is incised during trigger finger release.

2. The A2 pulley, which overlies the proximal end of the proximal phalanx. It must be preserved (if at all possible) to prevent bowstringing.

3. The A3 pulley, which lies over the proximal interphalangeal joint.

4. The A4 pulley, which is located about the middle of the middle phalanx. It must be preserved to prevent bowstringing.

 

Cruciate pulleys, none of which are critical for flexor function, include the following:

1. The C1 pulley, which is located over the middle of the proximal phalanx

2. The C2 pulley, which is located over the proximal end of the middle phalanx

3. The C3 pulley, which is located over the distal end of the middle phalanx

 

 

 

Figure 5-61 The annular and cruciate ligaments of the flexor tendon sheath, lateral view. Note the relationship of the pulleys to the skin creases and joint lines.

 

The two tendons enter the fibroosseous canal with the superficialis tendon on top of the profundus tendon. Over the proximal phalanx, the superficialis tendon divides into halves, which spiral around the profundus tendon, meeting on its deep surface and forming a partial decussation

(chiasma). The two then run as one tendon underneath the profundus tendon before attaching to the base of the middle phalanx. Thus, the superficialis tendon actually provides part of the bed on which the profundus tendon runs. Distal to the attachment of the superficialis tendon, the profundus tendon inserts into the base of the terminal phalanx (see Fig. 5-77). Within the fibroosseous sheath, the nutrition of the flexor tendons is provided for by blood vessels that enter the tendons from synovial folds called vincula (Fig. 5-62).

Extremely difficult conditions for full recovery exist after lacerations in zone 2, mainly because the flexor tendons are enclosed within a nondistensible fibroosseous canal, and also because, for full function, the tendons must run over each other. It is important to remember that any adhesion between the two can cause malfunction of the involved finger.

Repairs in this zone have the worst prognosis of all the zones.34 It has been nicknamed “no-man’s land” by Bunnell.35

Zone 1

Zone 1 is the area distal to the insertion of the superficialis tendon. Although the profundus tendon still is enclosed tightly within a fibroosseous sheath here, it runs alone. Therefore, the prognosis for the repair of lacerations in this zone is better than that for zone 2, although not as good as that for zones 3, 4, and 5.

 

 

 

Figure 5-62 The vincula longa and brevia are main blood supplies to the flexor tendons. Note the relationship of the vincula to the flexor tendon synovial sheath (inset).

Vascular Supply of the Tendons

 

Within the fibrous sheath, the flexor tendons are enveloped in a double layer of synovium (see Fig. 5-62, inset). Each tendon receives its blood supply from arteries that arise from the palmar surface of the phalanges. These vessels are encased in the vinculum (mesotendon). Two vincula supply each tendon, as follows:

1. Profundus tendon.

   1. The short vinculum runs to the tendon close to its insertion onto the distal phalanx.

   2. The long vinculum passes to the tendon from between the halves of the superficialis tendon at the level of the proximal phalanx.

2. Superficialis tendon.

   1. The short vinculum runs to the tendon near its attachment onto the middle phalanx.

   2. The long vinculum is a double vinculum, passing to each half of the tendon from the palmar surface of the proximal phalanx.

 

Injection studies on fresh cadaveric material have found that this classic arrangement does not always hold true. The long vincula to both tendons may be absent in the long or ring fingers. When they are present, the long vinculum to the superficialis tendon may attach to either or both of its slips, and the long vinculum to the profundus tendon may arise at the level of the insertion of the superficialis tendon.36

These variations should be borne in mind as the flexor tendons are explored within their sheaths. The vincula should be preserved, if possible, to preserve the blood supply to the tendon. They also have some mechanical function,37 which occasionally may mask the diagnosis of acute tendon damage.

Other injection studies have found that the volar aspects of the flexor tendons are largely avascular; their nutrition may be derived from synovial fluid. Therefore, sutures placed in the volar aspects of the tendons do not interfere materially with the blood supply to the tendons themselves.38

 

Landmarks and Incision

 

The critical landmarks of hand surgery are the skin creases, all of which are situated where the fascia attaches to the skin. There are four major

creases: The distal palmar crease corresponds roughly to the palmar location of the metacarpophalangeal joints and the location of the proximal (A1) pulley, the palmar digital crease marks the palmar location of the A2 pulley, the proximal interphalangeal crease marks the proximal interphalangeal joint, and the thenar crease outlines the thenar eminence (see Figs. 5-44, 5-60, and 5-61).

The nerve supply to the skin of the fingers comes from two sources: The volar aspect is supplied by the volar digital nerves, and the dorsal aspect is innervated by the dorsal nerves of the radial and ulnar nerves, as well as by the dorsal contribution from the volar digital nerves for the distal 1½ phalanges of the index, long, and ring fingers. The dorsum of the thumb and small finger are served exclusively by the radial and ulnar nerves, respectively. Because of this anatomic arrangement, the midlateral approach to the flexor sheath does not cause skin denervation (see Fig. 5-50).

 

Volar Approach to the Scaphoid

The volar approach provides good exposure of the scaphoid bone.39 It also avoids damaging the dorsal blood supply to the bone’s proximal half, as well as the superficial branch of the radial nerve. It does pose a threat to the radial artery, however, which is close to the operative field. It leaves a more cosmetic scar than the dorsal approach, and its uses include the following:

1. Bone grafting for nonunion of the scaphoid

2. Excision of the proximal third of the scaphoid

3. Excision of the radial styloid, either alone or combined with one of the above procedures

4. Open reduction and internal fixation of fractures of the scaphoid. In such cases this approach frequently is combined with the dorsolateral approach to the scaphoid.

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm lying on an arm board. Supinate the forearm to expose the volar aspect of the wrist, and apply an exsanguinating bandage and tourniquet (see Fig. 5-15).

Landmarks and Incision

Landmarks

Palpate the tubercle of the scaphoid on the volar aspect of the wrist, just distal to the skin crease of the wrist joint.

The flexor carpi radialis muscle lies radial to the palmaris longus muscle at the level of the wrist. It crosses the scaphoid before inserting into the base of the second and third metacarpal just on the ulnar side of the radial pulse.

Incision

Make a vertical or curvilinear incision on the volar aspect of the wrist, about 2 to 3 cm long. Base it on the tubercle of the scaphoid and extend it proximally between the tendon of the flexor carpi radialis muscle and the radial artery (Fig. 5-63).

 

Internervous Plane

 

There is no true internervous plane; the only muscle mobilized is the flexor carpi radialis (which is supplied by the median nerve).

 

 

 

Figure 5-63 Incision for the volar approach to the scaphoid. Base the incision on

the tubercle of the scaphoid and extend it proximally and distally. The proximal extension is between the tendon of the flexor carpi radialis and the radial artery.

 

Superficial Surgical Dissection

 

Incise the deep fascia in line with the skin incision and identify the radial artery on the lateral (radial) side of the wound (Fig. 5-64). Retract the radial artery and lateral skin flap to the lateral side. The superficial palmar branch of the artery which runs close to the scaphoid tubercle may cross the operative field and need ligation. Identify the tendon of the flexor carpi radialis muscle and trace it distally, incising that portion of the flexor retinaculum that lies superficial to it. After the tendon has been freed from its tunnel in the flexor retinaculum, retract it medially to expose the volar aspect of the radial side of the wrist joint (Fig. 5-65).

 

 

 

Figure 5-64 Incise the deep fascia between the radial artery and the flexor carpi radialis.

 

 

Figure 5-65 Retract the radial artery and skin flap laterally and the flexor carpi radialis medially to expose the volar aspect of the radial side of the wrist joint capsule.

 

Deep Surgical Dissection

 

Incise the capsule of the wrist joint obliquely over the scaphoid to expose the distal two-thirds of the scaphoid. Begin at the tubercle of the scaphoid distally and extend the incision proximally until palmar rim of the distal radius is reached. Try to preserve as much of the palmar ligament complex as possible to stabilize the proximal pole of the scaphoid. This anterior area of bone is nonarticular. To gain the best view of the proximal third of the bone, place the wrist in marked dorsiflexion (Fig. 5-66).

 

 

Figure 5-66 Incise the joint capsule. Dorsiflex the wrist to gain exposure of the proximal articular third of the bone.

 

 

Dang

 

 

Vessels

The radial artery lies close to the lateral border of the wound and can be incised accidentally at any time during the dissection. Therefore, it must be identified early in the procedure. The superficial palmar branch of the artery usually crosses the operative field and needs to be ligated to prevent a postoperative hematoma.

 

How to Enlarge the Approach

 

The incision can be extended usefully to a limited extent. Proximally, extend the skin incision along the line of the flexor carpi radialis muscle. Identify the distal border of the pronator quadratus muscle and elevate it gently from the underlying bone. This will create adequate exposure of the distal end of the radius, allowing a bone graft to be taken from this site. Adequate exposure also will be obtained to allow excision of the radial styloid, if this is indicated.

The key to exposing the scaphoid lies in forceful dorsiflexion of the

wrist. This will expose the proximal pole of the scaphoid, which is the site of most cases of nonunion. If the location of the fracture is not completely clear, place a small, radiopaque mark at the operative site and carry out a radiographic examination on the operating table. Bone grafting can be carried out adequately with this exposure, but the insertion of a screw may require a combined dorsal and volar approach to the scaphoid.40

 

Dorsolateral Approach to the Scaphoid

The dorsolateral approach offers an excellent and safe exposure of the scaphoid bone. Its major drawback is that it endangers the superficial branch of the radial nerve, and it also may interfere with the dorsal blood supply of the scaphoid.41 Its uses include the following:

1. Bone grafting for nonunion

2. Excision of the proximal fragment of a nonunited scaphoid

3. Excision of the radial styloid in combination with either of the two above procedures

4. Open reduction and internal fixation of fractures of the scaphoid. When this approach is used for this indication, it is frequently combined with a volar approach to the scaphoid.40

5. Repair of complete ruptures of the scapholunate ligament

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm extended on an arm board. Pronate the forearm to expose the dorsoradial aspect of the wrist, and apply an exsanguinating bandage and tourniquet (see Fig. 5-1).

 

Landmarks and Incision

Landmarks

The radial styloid process is truly lateral when the hand is in the anatomic position. Palpate it in this position and then pronate the arm, keeping a finger on the styloid process.

The anatomic snuff-box is a small depression that is located immediately distal and slightly dorsal to the radial styloid process. The scaphoid lies in the floor of the snuff-box. Ulnar deviation of the wrist causes the scaphoid to slide out from under the radial styloid process, and

it becomes palpable. The radial pulse is palpable in the floor of the snuff-box, just on top of the scaphoid.

The first metacarpal can be palpated between the snuff-box and the metacarpophalangeal joint.

Incision

Make a gently curved, S-shaped incision centered over the snuff-box. The cut should extend from the base of the first metacarpal to a point about 3 cm above the snuff-box (Fig. 5-67).

 

Internervous Plane

 

There is no true internervous plane, because the plane of dissection falls between the tendons of the extensor pollicis longus and extensor pollicis brevis muscles, both of which are supplied by the posterior interosseous nerve. Because both muscles receive their nerve supply well proximal to this dissection, using this plane does not cause denervation.

 

Superficial Surgical Dissection

 

Identify the tendons of the extensor pollicis longus muscle dorsally and the extensor pollicis brevis muscle ventrally (Fig. 5-68). To confirm their identity, pull on the tendons and observe their action on the thumb. Open the fascia between the two tendons, taking care not to cut the sensory branch of the superficial radial nerve, which lies superficial to the tendon of the extensor pollicis longus muscle. Usually the radial nerve has divided into two or more branches at this level. Both branches cross the interval between the tendons of the extensor pollicis brevis and the extensor pollicis longus, lying superficial to the tendons. Their course is variable, and they must be sought and preserved during superficial dissection (see Figs. 5-67 and 5-68).

 

 

Figure 5-67 Incision for dorsolateral approach to the scaphoid. Make a gently curved S-shaped incision centered over the snuff-box. The superficial branch of the radial nerve crosses directly beneath the incision.

 

Now, separate the tendons, retracting the extensor pollicis longus dorsally and toward the ulna, and the extensor pollicis brevis ventrally. Identify the radial artery as it traverses the inferior margin of the wound, lying on the bone (Fig. 5-69). Find the tendon of the extensor carpi radialis longus muscle as it lies on the dorsal aspect of the wrist joint. Mobilize it and retract it in a dorsal and ulnar direction, together with the tendon of the extensor pollicis longus muscle, to expose the dorsoradial aspect of the wrist joint.

 

Deep Surgical Dissection

 

Incise the capsule of the wrist joint longitudinally (Fig. 5-70). Reflect the capsule dorsally and in a volar direction to expose the articulation between the distal end of the radius and the proximal end of the scaphoid. The radial artery retracts radially and in a volar direction with the joint capsule.

Place the wrist in ulnar deviation and continue stripping the capsule off the scaphoid to expose the joint completely (Fig. 5-71). Try to preserve as much soft tissue attachments to the bone as possible especially in the region of the dorsal ridge. Modern aiming guides have substantially reduced the need for radial dissection in open reduction and internal fixation of scaphoid fractures.

 

 

Figure 5-68 Identify the superficial branch of the radial nerve and retract it with the dorsal skin flap. Identify the tendons of the extensor pollicis longus dorsally and the extensor pollicis brevis ventrally. Incise the fascia between the tendons.

 

 

 

Figure 5-69 Retract the extensor pollicis longus dorsally and the extensor pollicis brevis ventrally. Identify the radial artery and its dorsal carpal branch, taking care to preserve the arterial branch.

 

 

Figure 5-70 Incise the joint capsule. The scaphoid is exposed.

 

 

 

Figure 5-71 Place the wrist in ulnar deviation to expose the proximal third of the scaphoid in its entirety.

 

 

Figure 5-72 Blood supply to the scaphoid. Most branches enter the scaphoid from the dorsal aspect. These branches must be preserved to prevent necrosis of its proximal fragment.

 

 

Dang

 

 

Nerves

The superficial radial nerve is at risk during this exposure. Because it lies directly over the tendon of the extensor pollicis longus muscle, it is extremely easy to cut as the tendon is mobilized. Incising the nerve may produce a troublesome neuroma, as well as an awkward (although not handicapping) area of hypoesthesia on the dorsal aspect of the hand.

Arteries

The blood supply to the proximal pole of the scaphoid comes from the dorsal carpal branch of the radial artery (see Fig. 5-72). These branches are at risk during incision of the joint capsule and must be preserved if possible.

 

Drainage of Pus in the Hand

Hand infections are an important source of patient morbidity. They cause an enormous loss of time from work and can produce permanent deficits in hand function.42

Until recently, the availability of more prompt medical care and the administration of antibiotics had caused a dramatic decrease in the incidence of major hand infections; however, the intravenous and subcutaneous use of narcotics among drug addicts has increased, reintroducing serious hand infections to the field of surgery.

The keys to the surgical treatment of hand infections are as follows:

1. Accurate localization of the infection. Each particular infection has characteristic physical signs, according to the anatomy of the particular compartment that is infected.

2. Timing of the operation. The timing of surgical drainage is critical to the outcome of surgical treatment. If an infection is incised too early, the surgeon may incise an area of cellulitis and actually cause the infection to spread. In contrast, if pus is left in the hand too long, particularly around the tendon, it may induce irreversible changes in the structures it surrounds.

The correct timing for a given surgical procedure is difficult to determine. In the body, the cardinal physical sign of an abscess is the presence of a fluctuant mass within an area of inflammation; however, because there often is only a small amount of pus present in the hand, an abscess there can be hard to find. In addition, pus frequently is found in tissues that contain fat. At body temperature, fat itself is fluctuant, further complicating the physical diagnosis of an abscess. Nevertheless, some guidelines for the detection of pus do exist:

1. Pus may be seen subcutaneously.

2. The longer an infection has been present, the more likely it is that pus will be present. Infections of less than 24 hours’ duration are unlikely to have developed pus.

3. Classically, if the patient cannot sleep at night because of pain in the hand, pus probably has formed.

4. If slight passive extension of the finger produces pain along the finger and in the palm, the tendon sheath is likely to be infected; it should be explored to drain the pus.

The last guideline, signs of tendon sheath infection, is one of the four cardinal signs of acute suppurative tenosynovitis described by Kanavel.43

The other three follow below:

1. Swelling around the tendon sheath

2. Tenderness to palpation

3. Flexion deformity of the affected finger

Despite these guidelines, it still may be difficult to determine whether there is pus in the hand. If doubt exists, elevate the arm and treat the patient with intravenous antibiotics and warm soaks, reexamining him or her at frequent intervals. If signs of inflammation diminish rapidly, avoid surgery.

 

Optimum Operative Conditions

1. Use a general anesthetic or a distal nerve block. Injecting a local anesthetic at the site of infection is ineffective and actually may spread the infection within fascial planes.

2. Use a tourniquet. The arm should not be exsanguinated with a bandage, to avoid spreading the infection by mechanical compression. The arm should be elevated for 3 minutes before the tourniquet is applied.

3. Perfect lighting is critical for all explorations of pus in the hand. All relevant neurovascular bundles must be identified to ensure their preservation.

4. Draining abscesses of the hand is not like draining abscesses anywhere else in the body. Boldly incising an abscess space without approaching it carefully is to be condemned.

5. Leave all wounds open after incision.

6. Immobilize the hand in the functional position after surgery by applying a dorsal or volar splint, or both, with the metacarpophalangeal joints at 80 degrees of flexion and the proximal and distal interphalangeal joints at 10 degrees of flexion. At this position, the collateral ligaments of the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints are at their maximum length and will not develop contractures during immobilization.

7. Elevate the arm postoperatively. Continue administering intravenous antibiotics until signs of inflammation begin to diminish. Mobilize the affected part as soon as signs of inflammation subside. Begin extensive rehabilitation, which may last several months.

 

Of the eight major infection sites listed below, the first three are seen most

often:

1. Paronychia

2. Pulp space (felon)

3. Web space

4. Tendon sheath

5. Deep palmar area

   1. Lateral space (thenar space)

   2. Medial space (midpalmar space)

6. Radial bursa

7. Ulnar bursa

8. Osteomyelitis, pyarthrosis

Surgical approaches to each of these areas are discussed below.

 

Drainage of Paronychia

Paronychia is infection of a nail fold. Perhaps the most common hand infection, it is caused most often by Staphylococcus aureus. It occurs in individuals from all walks of life.1 Hairdressers often are affected because hair from their clients may become embedded between the cuticle and the bony nail. Tearing the cuticle to remove a “hangnail” probably is the most common cause of this infection.

It usually is easy to see where the pus distends the cuticle. The paronychia may occur on either side or it may lift the whole of the cuticle upward. It even may extend underneath the nail.

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm extended on an arm board (see Fig. 5-15).

 

 

Figure 5-73 A–D: Incisions for the evacuation of pus at the base of the nail (paronychia).

 

Incision

 

Make a short, longitudinal incision at one or both corners of the nail fold (Fig. 5-73A).

 

Internervous Plane

 

There is no internervous plane involved. The nerve supply of the skin in this region is derived from cutaneous nerves that overlap one another considerably. No area of skin becomes denervated.

 

Superficial Surgical Dissection

 

Raise the skin flap outlined by the skin incision at the base of the nail, evacuating the pus between the cuticle and the nail. If pus extends under the nail, excise either one corner of the base of the nail or half of the nail itself, depending on how it has been undermined and lifted off the nail bed (see Fig. 5-73B,C). Occasionally, a nick into the soft tissue cuticle parallel with the nail will release the pus (see Fig. 5-73D).

 

 

Dang

 

 

If the nail bed is damaged, the new nail will develop a ridge, which is a minor but permanent cosmetic deformity.

How to Enlarge the Approach

 

The approach cannot be extended usefully by either local or extensile measures.

 

Drainage of a Pulp Space Infection (Felon)

 

 

Distal finger pulp space infections are the hand infections that most often require surgical drainage. Infection is usually caused by a penetrating injury to the pulp, an injury that may be quite trivial in itself. Superficial infections cause skin necrosis and point early, usually on the volar aspect of the pulp. Deeper infections are more likely to cause osteomyelitis of the underlying distal phalanx.

Depending on the depth of the infection, two different techniques exist for draining pus in this site:

1. If the abscess is pointing in a volar direction in the distal pulp of the finger, as it commonly is, make a small incision on the lateral side of the volar surface and enter the abscess cavity obliquely. Midline incisions may produce painful scars.

2. If the abscess is deep, the surgery described below may be necessary.

 

Position of the Patient

 

Place the patient on the operating table, with the arm lying on an arm board.

 

Incision

 

Make a straight incision on the lateral aspect of the terminal phalanx of the finger, extending to the tip of the finger close to the nail. The incision should not extend proximally to the distal interphalangeal joint; more proximal incisions may damage the digital nerve, causing a painful neuroma, or they may contaminate the joint with purulent material.

 

 

Figure 5-74 Incision for drainage of pulp space infection (felon). The septa must be cut to ensure appropriate drainage.

 

The incision should be dorsal and distal to the distal end of the distal interphalangeal crease (Fig. 5-74). It should not extend distally beyond the distal corner of the nail. Avoid the ulnar aspect of the thumb and the radial aspect of the index and long fingers to avoid creating a scar that interferes with pinch.

 

Internervous Plane

 

There is no internervous plane in this incision. The skin incision lies between skin that is supplied by the dorsal cutaneous nerve and skin that is supplied by branches of the volar digital nerves.

 

Superficial Surgical Dissection

 

The pulp of the terminal phalanx contains numerous fibrous septa that connect the distal phalanx with the volar skin, creating loculi. The infection easily can invade several of these loculi. To ensure that all pockets of infection are drained, deepen the skin incision transversely across the pulp of the finger, remaining on the volar aspect of the terminal phalanx, until the skin of the opposite side of the finger is reached. Do not penetrate this skin (see Fig. 5-74). Now, bring the scalpel blade distally, detaching the origins of the fibrous septa from the bone. Proximally, take care not to extend the dissection beyond a point 1 cm distal to the distal interphalangeal crease; otherwise, the flexor tendon sheath may be damaged and infection introduced into it.

 

 

Dang

 

 

Nerves

The digital nerves may be damaged if the skin incision drifts too far proximally. Painful neuromas can result without an appreciable area of

hyperesthesia on the finger.

Muscles and Ligaments

The fibrous flexor sheath of the profundus tendon may be incised accidentally if the incision is carried too far proximally.

 

Special Points

 

The fibrous septa that connect the distal phalanx to the skin make this an ideal site for loculation of pus. Take care to open all the loculi so that adequate drainage takes place. Unsuccessful treatment of a deep abscess may result in osteomyelitis of the distal phalanx.

 

How to Enlarge the Approach

 

The approach cannot be enlarged usefully by either local or extensile measures.

 

Web Space Infection

Web space infections, which involve pus in one of the four webs of the palm, are quite common. The abscess usually points dorsally, because the skin on the dorsal surface of the web is thinner than the skin on the palmar surface. Characteristically, a large amount of edema appears on the dorsum of the hand, and the two fingers of the affected web are spread farther apart than normal (Fig. 5-75).

The web spaces all communicate via the canal of the lumbrical muscles into the palm; therefore, a neglected web space infection can cause a more extensive infection by spreading up the lumbrical canal and into the palm.

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm on an arm board. Use a general anesthetic or an axillary or brachial block, then raise the arm for 3 minutes before inflating an arm tourniquet (see Fig. 5-15).

 

 

Figure 5-75 Web space infection. A large amount of edema usually appears on the dorsum of the hand, and the two fingers of the affected web space are spread farther apart than normal.

 

Incision

 

Two skin incisions are possible—longitudinal and transverse. Make a longitudinal incision in the volar skin of the palm centered over the middle of the affected web space. Alternatively, make a transverse incision following the contour of the web space about 5 mm proximal to it (Fig. 5-76).

 

Internervous Plane

 

There is no true internervous plane in this approach.

 

Superficial Surgical Dissection

 

Carefully deepen the skin incision by blunt dissection. The digital nerves and vessels lie immediately under the incision and may be damaged if the cut is too deep and a transverse incision is used. The abscess cavity usually is located just below the skin; it can be entered with very little additional dissection.

 

 

Dang

 

Nerves

Both digital nerves of the web space are vulnerable with the transverse skin incision. If used make sure that an effective tourniquet, proper lighting, and fine instruments are used in the operation. As long as the skin is incised with care, the nerves should not be damaged.

 

 

 

Figure 5-76 Make a longitudinal or curved transverse incision in the volar skin of the palm.

 

Longitudinal incisions in the web space avoid the threat to the neurovascular bundle, but scarring during the healing process may reduce significantly the ability of the two fingers of the web space to separate.

 

How to Enlarge the Approach

 

The approach cannot be extended usefully. Some surgeons recommend a second, dorsal, skin incision over the pointing area to improve drainage without appreciably increasing the morbidity of the procedure.

 

Anatomy of the Web Space of the

 

Fingers

There are three webs between the four fingers. The spaces are surprisingly long (about 2 cm) extending from the edge of the skin to the metacarpophalangeal joints. They contain both the superficial and the deep transverse ligaments of the palm, the digital nerves and vessels, and the tendons of the interossei and lumbricals. Between these various structures lies loose, fibrous, fatty tissue, tissue that can be displaced easily by infection and the formation of abscesses (Fig. 5-77; see Fig. 5-40).

 

 

 

Figure 5-77 Anatomy of the web space. The neurovascular bundle runs deep to or dorsal to the superficial transverse ligament (natatory ligament) and palmar to the deep transverse metacarpal ligament. The lumbrical muscle runs along with the neurovascular bundle palmar to the deep transverse ligament, whereas the interossei pass dorsal to the deep transverse metacarpal ligament.

The important structures in the web space are listed below:

1. Superficial transverse ligament of the palm (natatory ligament). This ligament lies immediately beneath the palmar skin and supports the free margins of the webs. The ligament runs superficial (palmar) to the digital nerves and vessels, and attaches to the palmar aponeurosis.

2. Digital nerves and vessels. These structures lie immediately deep to the superficial transverse ligament of the palm, with the nerves on the palmar side of the arteries.

3. Tendons of the lumbricals. These muscles arise from the four tendons of the flexor digitorum profundus muscle in the middle of the palm. Each lumbrical tendon passes along the radial side of its metacarpophalangeal joint before inserting into the extensor expansion on the dorsum of the proximal phalanx. Infection in the web space can spread proximally along the lumbrical tendon and enter the palm (see Fig. 5-79).

4. Deep transverse ligament of the palm. This strong ligament connects the volar plates (palmar ligaments) of the metacarpophalangeal joints. It is 3 to 4 cm proximal to the superficial transverse ligaments. The lumbrical tendons are volar or palmar to it, as is the neurovascular bundle (see Fig. 5-77).

5. Interosseous tendons. These muscles, which arise from the metacarpals, insert into the dorsal expansion over the proximal phalanges. Their tendons pass dorsal to the deep transverse ligament, in contrast to the lumbrical tendons, which pass on the ligament’s volar side (see Fig. 5-77).

 

Anatomy of the Web Space of the Thumb

The thumb is far more mobile than are any of the fingers. Its increased mobility is reflected in the unique anatomy of its web space: Both the superficial and the deep transverse ligaments are absent and the bulk of the web is filled with two muscles, the transverse head of the adductor pollicis and the first dorsal interosseous (see Figs. 5-40 to 5-42).

 

Adductor Pollicis Muscle

 

See the section regarding the anatomy of the palm.

First Dorsal Interosseous Muscle

 

The dorsal interosseous muscle is the largest of all the interossei. It arises from the adjacent borders of the first and second metacarpals, runs deep (dorsal) to the adductor pollicis, and inserts into the fibrous extensor expansion on the dorsum of the index finger. The muscle bulk provides most of the substance of the thumb’s web space; wasting is easy to detect clinically by gently pinching the web while the patient pinch grips. The pinch also forms the basis for one test of an ulnar nerve lesion, because the muscle is supplied by the ulnar nerve (see Fig. 5-11).

 

Arteries

 

Two branches of the radial artery, the radialis indicis and the princeps pollicis, emerge from between the two muscles of the thumb web. The radialis indicis artery runs to the radial border of the index finger, and the princeps pollicis goes to the thumb, where it divides into two palmar digital arteries. Approaches made in the center of the web space avoid damage to either artery (see Fig. 5-42).

 

Tendon Sheath Infection

An infection within the synovial sheath of the flexor tendons is one of the most serious of all hand infections. Prompt surgical drainage is critical, for a long-standing infection almost always results in fibrosis within the tendon sheath and subsequent tethering of the tendon itself. Sheath infections are caused by spread from a pulp infection or by puncture wounds, particularly at the flexor creases.

The diagnosis is made clinically. The finger held in a flexed position is grossly swollen and tender. The slightest active or passive extension of the digit produces severe pain, which is the cardinal physical symptom on which the diagnosis is based.

These infections are not as common as they used to be as a result of earlier diagnosis and treatment of superficial finger infections. Nevertheless, they still occur and offer a true orthopedic emergency.

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm extended on

an arm board. A tourniquet is essential, but the arm should not be exsanguinated as it is with general anesthesia or a proximal local block (either brachial or axillary). Good lighting and fine instruments minimize the risk of damaging the vital structures within the hand (see Fig. 5-15).

 

Landmarks and Incision

Landmarks

The distal palmar crease roughly marks the palmar site of the metacarpophalangeal joints and the proximal border of the fibrous flexor sheath of the flexor tendons.

The distal interphalangeal crease is the surface marking of the distal interphalangeal joint and lies just proximal to the distal end of the fibrous flexor sheath.

Incision

Make a small transverse incision just proximal to the distal palmar crease and over the infected flexor tendon. The incision should be 1.5 to 2.0 cm long (Fig. 5-78).

A second incision usually is necessary if there is turbid fluid within the sheath. Make a midlateral cut over the distal end of the middle phalanx in the line connecting the dorsal ends of the proximal and distal interphalangeal creases (see Fig. 5-78A).

 

 

Figure 5-78 Incision for infection of the flexor digital sheath. Make a small transverse incision just proximal to the distal palmar crease, over the infected flexor tendon. A: A second incision may be necessary, and this should be made over the distal end of the middle phalanx in the midlateral position. B: Separate the longitudinally running fibers of the palmar aponeurosis. C: Incise the A1 pulley to reveal the underlying synovial sheath, which then should be opened.

 

Internervous Plane

 

There is no internervous plane in this approach. The midlateral approach is roughly in the line of demarcation between skin that is supplied by the digital nerves and skin that is supplied by the dorsal cutaneous nerves.

 

Superficial Surgical Dissection

 

Separate the longitudinally running fibers of the palmar aponeurosis by blunt dissection, by opening a closed hemostat so that the dissection is

carried out parallel to, rather than across, the main neurovascular bundles of the palm (see Fig. 5-78B). Proceed deeper onto the proximal end of the fibrous flexor sheath. At this level, the proximal (A1) pulley is visible. Incise the pulley longitudinally to reveal turbid fluid or, more rarely, frank pus (see Fig. 5-78C). If turbid fluid is found, make the second skin incision and deepen it, coming down dorsal to the digital nerves and vessels. Incise the fibrous flexor sheath at the distal end of the middle phalanx.

This second incision allows through-and-through irrigation to be carried out, if it is required (see Fig. 5-78A).

 

 

Dang

 

 

Nerves and Vessels

The digital nerves and vessels are at risk in both incisions. If the skin incision in the finger is made too far in a volar direction, it may threaten the neurovascular bundle. The bundle is safe as long as the skin incision remains just dorsal to the dorsal end of the proximal and distal interphalangeal creases (see Fig. 5-78 and Midlateral Approach to the Flexor Sheaths, page 224).

Because the skin palmar incision crosses the neurovascular bundles at right angles, and because the bundles lie immediately deep to the palmar aponeurosis, the bundles may be damaged by overzealous incision of the skin. Separating the fibers of the palmar aponeurosis by blunt dissection in the line of the fibers avoids damage to the nerves.

 

How to Enlarge the Approach

 

The approach cannot be enlarged effectively. Infections in the radial or ulnar bursae require a separate incision.

 

Deep Palmar Space Infection

Deep palmar infections are extremely serious; they often lead to diminished hand function. The infected area usually lies deep to the flexor tendons and lumbricals, but superficial to the metacarpals and their muscles, the adductor pollicis and the interossei.

The central compartment of the palm is subdivided by a septum of fascia that arises from the fascia surrounding the flexor tendons of the

middle finger and attaches to the third metacarpal. The area on the lateral side of the septum sometimes is called the thenar space, and the area on the medial side is called the midpalmar space. In this text, the terms lateral space and medial space are used, because the term thenar space can be confusing, as this area has nothing to do with the space that is occupied by the thenar muscles of the thenar eminence (Fig. 5-79; see Fig. 5-41).

Infections of the medial space cause local pain, tenderness, and swelling of the palm. The middle and ring fingers lose their ability to move actively, and moving them passively produces severe pain. The hand is grossly swollen, resembling an inflated rubber glove.

Infections of the lateral space produce symptoms and signs similar to those of infections of the medial space, but the index finger and thumb are the digits that lose the ability to move.

Deep palmar infections are among the rarest encountered in hand surgery. These deep infections are being seen more frequently now, however, primarily because of the increase in drug addiction. More than any other infection in the hand, they can cause systemic illness associated with high fevers.

 

 

 

Figure 5-79 Within the central compartment of the palm, a potential deep space

exists between the undersurface of the flexor tendons and the upper surfaces of the interossei and adductor pollicis muscles. This deep palmar space is subdivided into medial midpalmar and lateral thenar spaces by the oblique septum that arises from the connective tissue surrounding the middle finger flexor tendons and runs to the palmar surface of the middle metacarpal. Infections involving the web space may travel along the lumbrical muscle to enter these two potential spaces.

 

Drainage of the Medial (Midpalmar) Space

 

 

Incision

 

Make a curved transverse incision on the palm just proximal to the distal palmar crease and over the swelling. The length of the incision should be determined by the size of the abscess to be drained (Fig. 5-80).

 

Internervous Plane

 

There is no internervous plane in this approach.

 

Superficial Surgical Dissection

 

Incise the skin carefully; the line of the skin incision crosses the paths of the digital nerves. Open the palmar fascia by blunt dissection at the distal end of the wound and identify the long flexor tendon to the ring finger. Enter the medial midpalmar space by blunt dissection on the radial border of this tendon (Figs. 5-81 to 5-83).

 

 

Dang

 

 

Nerves

The digital nerves to the little and ring fingers run immediately under the palmar aponeurosis and cross the line of the skin incision. No part of the palmar aponeurosis should be incised transversely until these nerves have been dissected out fully (see Fig. 5-82).

 

 

Figure 5-80 Incision for drainage of the medial space (midpalmar space).

 

 

Figure 5-81 Open the palmar fascia by blunt dissection at the distal end of the wound.

 

 

Figure 5-82 The flexor digitorum superficialis tendon to the ring finger is identified. The neurovascular structures run parallel to it on each side, and the lumbrical is visible on its radial side.

 

 

Figure 5-83 The deep palmar space is entered by retracting the lumbrical and its tendon medially.

 

Vessels

The digital arteries run with the digital nerves and also may be in danger. For this reason, the digital arteries should be identified before the palmar aponeurosis is incised.

 

How to Enlarge the Approach

 

The incision, which is a drainage procedure, cannot be extended usefully.

 

Drainage of the Lateral (Thenar) Space

 

Incision

Make a curved incision about 4 cm long, just on the ulnar side of the thenar crease (Fig. 5-84).

 

Internervous Plane

 

There is no internervous plane in this approach.

 

Superficial Surgical Dissection

 

Deepen the dissection in line with the skin incision, taking care to identify and preserve the digital nerves to the index finger. Identify the flexor digitorum superficialis tendon to the index finger (Figs. 5-85 and 5-86). Deep to these tendons is the lateral space; enter it by blunt dissection (Fig. 5-87).

 

 

Dang

 

 

Nerves

The digital nerves to the index finger are directly in line with the skin incision. Take care not to damage them during incision of the palmar aponeurosis.

The motor branch to the thenar muscles emerges from the deep surface of the median nerve as the median nerve leaves the carpal tunnel. Note, however, that the location of its division from the median nerve is quite variable. This nerve hooks around the distal end of the flexor retinaculum to supply the muscles. Make sure to identify the branch at the proximal end of the incision so as to avoid damaging it (see Fig. 5-39).

 

 

Figure 5-84 Incision for drainage of the lateral space (thenar space). The incision is made just to the ulnar side of the thenar crease.

 

 

Figure 5-85 Identify the palmar fascia and spread it in line with its fibers over the flexor tendon to the index finger.

 

 

Figure 5-86 Identify the flexor tendon to the index finger. The neurovascular bundles lie to each side. The lumbrical is seen on the radial side.

 

 

Figure 5-87 Retract the tendon and lumbrical radially, and enter the space beneath them by blunt dissection.

 

Applied Surgical Anatomy of the Deep Palmar Space

 

 

The palm is divided into spaces by fibrous septa that pass through it before attaching to the metacarpals. There are two major septa: The thenar septum originates from the palmar aponeurosis and inserts into the first metacarpal, separating the three muscles of the thenar eminence from the central palmar structures; and the hypothenar septum originates on the ulnar side of the palmar aponeurosis and inserts into the fifth metacarpal, separating the three muscles of the hypothenar eminence from the central palmar structures (see Figs. 5-41 and 5-79).

Thus, the palm is divided into three compartments: A thenar compartment, a hypothenar compartment, and a central compartment.

The central compartment contains the long flexor tendons to the fingers and the adductor pollicis muscle, as well as the digital nerves and vessels and the superficial and deep palmar arches.

Within the central compartment, a potential deep space exists between the undersurface of the flexor tendons and the upper surface of the interosseous and adductor pollicis muscles. This deep palmar space is divided into medial (midpalmar) and lateral (thenar) spaces by the oblique septum that arises from the connective tissue surrounding the middle finger flexor tendons and runs to the palmar surface of the middle metacarpal.44 This septum is the anatomic basis for the clinical division of deep palmar infection into two distinct, separate spaces.43

 

Lateral Space (Thenar Space)

 

The lateral space usually contains the first lumbrical muscle, which runs with the long flexor tendon to the index finger. Infections in the first web space may track down into the lateral space along the lumbrical muscle, although this is rare. Although lateral space infections may be drained through the first web space, such an incision is less effective than the procedure described in the previous section (see Figs. 5-84 to 5-87).

The space lies anterior to the adductor pollicis muscle. A second potential space exists behind that muscle and in front of the interossei. Infection of this “posterior adductor space” is very rare.45

 

Medial Space (Midpalmar Space)

 

The medial space contains the lumbrical muscles for the middle, ring, and little fingers, which run from the long flexor tendons of the middle, ring, and little fingers (the volar boundary of the space). The deep boundary is formed by the interossei and metacarpals of the third and fourth spaces. Thus, infection in the web spaces between the middle and ring fingers, and between the ring and little fingers, in theory, may spread to the medial space (see Fig. 5-79). The medial space may be drained through an incision in these webs, but the result is not as good as that obtained with direct drainage (see Figs. 5-80 to 5-83).

 

Drainage of the Radial Bursa

The long flexor tendon of the thumb is surrounded by a synovial sheath

that extends from the tendon’s insertion into the distal phalanx through the palm and carpal tunnel to the forearm just proximal to the proximal end of the flexor retinaculum. The proximal end of this sheath is known as the radial bursa (Fig. 5-88).

Infection of this space is diagnosed on the same clinical grounds as are infections of the synovial sheaths of the other fingers: Fusiform swelling of the thumb, with extreme pain on active or passive extension of the digit.

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm on an arm board. A general anesthetic or an axillary or brachial block is essential. Use a nonexsanguinating tourniquet and have an excellent light source available (see Fig. 5-15).

 

Landmark and Incision

Landmark

The interphalangeal crease of the thumb is the surface marking for the interphalangeal joint of the thumb. It lies just proximal to the distal end of the fibrous flexor sheath of the thumb.

Incision

Two incisions are required for complete drainage. First, make a small longitudinal incision on the lateral side of the proximal phalanx of the thumb, just dorsal to the dorsal termination of the interphalangeal crease (Fig. 5-89). Then, make a second incision over the medial aspect of the thenar eminence (beware of the motor branch) or on the volar aspect of the wrist (the proximal end of the radial bursa).

 

Internervous Plane

 

There is no internervous plane in this approach. The skin incision in the finger lies between skin that is supplied by the dorsal digital nerves and skin that is supplied by the volar digital nerves.

 

Superficial Surgical Dissection

 

Deepen the wound in line with the first skin incision, remaining dorsal to the radial neurovascular bundle of the thumb. Identify the fibrous flexor sheath covering the flexor pollicis longus tendon and incise it

longitudinally, just proximal to the tendon’s insertion into the distal phalanx. Incise the synovium within the sheath to drain the pus.

 

 

 

Figure 5-88 Anatomy of the synovial sheaths of the fingers and the radial and ulnar bursae.

 

 

 

Figure 5-89 Incision for drainage of the radial bursa. Two incisions are required

for complete drainage. Distally, make a small longitudinal incision on the lateral side of the proximal phalanx of the thumb, just dorsal to the interphalangeal crease. Make a second incision over the medial aspect of the thenar eminence on the volar aspect of the wrist, and carry the incision proximally to the end of the radial bursa. Care must be taken to protect the median nerve and its motor branch to the thenar muscles.

 

Now, pass a probe proximally along the flexor sheath until the point of the probe can be felt on the volar aspect of the wrist. Make a small longitudinal skin incision over this point and dissect carefully down to the probe. The tip of the probe may be proximal to the proximal end of the flexor retinaculum, or it may be actually in the carpal tunnel itself. If it is in the carpal tunnel, then formally incise the flexor retinaculum, taking great care not to damage the underlying median nerve with its motor branch to the thenar eminence. This is the only situation in which the median nerve is approached necessarily from its radial aspect in the carpal tunnel.

As is the case in the treatment of tendon sheath infections, a small catheter may be left in the distal end of the flexor sheath to irrigate the flexor tendon (Fig. 5-90).

 

 

Dang

 

 

If the midlateral approach to the thumb is made too far in a volar direction, its radial neurovascular bundle may be incised accidentally.

 

Special Points

 

Do not cut blindly down on the tip of the probe at the wrist; the median nerve, the motor branch of the median nerve, or the palmar cutaneous branch of the median nerve may be cut (see Applied Surgical Anatomy of the Volar Aspect of the Wrist).

 

How to Enlarge the Approach

 

This approach cannot be enlarged effectively by either local or extensile measures.

 

 

Figure 5-90 Identify the fibrous flexor sheath covering the flexor pollicis longus tendon and incise it longitudinally just proximal to the tendon’s insertion into the distal phalanx. Incise the synovium in the sheath to drain the pus and then pass a probe proximally along the flexor sheath. Make a small longitudinal incision over the probe at the level of the wrist to ensure complete drainage.

 

Drainage of the Ulnar Bursa

The synovial sheath surrounding the flexor tendons to the little finger extends from the insertion of the profundus tendon on the distal phalanx of the little finger to the volar aspect of the wrist, just proximal to the proximal end of the flexor retinaculum. The flexor tendons to the index, middle, and ring fingers also are invested by this layer of synovium as they pass through the carpal tunnel. The distal extension of the synovial compartment ends at the origin of the lumbrical muscle from the tendons to the ring, middle, and index fingers. It is known as the ulnar bursa (see Fig. 5-88).

Infection of the synovial sheath of the little finger may lead to infection of the ulnar bursa. The physical signs include a tenosynovitis affecting the

little finger, with active or passive extension producing extreme pain. In addition, pain may be referred to the palm when the other fingers are extended.

 

Position of the Patient

 

Place the patient supine on the operating table, with the arm extended on an arm board. Use a nonexsanguinating tourniquet and either a general anesthetic or a proximal local block (an axillary or brachial block).

 

Landmark and Incision

Landmark

The distal interphalangeal crease of the little finger is the surface marking for the distal interphalangeal joint. It lies just proximal to the distal end of the fibrous sheath of the little finger.

Incision

Make a short midline incision on the ulnar side of the little finger over the distal end of the middle phalanx (Fig. 5-91, inset). The incision should be just dorsal to the line connecting the dorsal termination of the proximal and distal interphalangeal creases. Make a second longitudinal incision on the lateral aspect of the hypothenar eminence at the level of the wrist.

 

Internervous Plane

 

There is no internervous plane. The finger skin incision lies between skin that is supplied by the dorsal digital nerves and skin that is supplied by the volar digital nerves.

 

Superficial Surgical Dissection

 

Deepen the approach in line with the incision, staying to the dorsal side of the neurovascular bundle. Identify the fibrous flexor sheath and incise it longitudinally. Next, incise the synovium to allow drainage of the pus. Pass a probe gently along the tendon until it can be felt on the volar aspect of the wrist, just proximal to the proximal end of the flexor retinaculum.

Carefully incise the skin longitudinally over the probe and dissect down to it layer by layer. The probe should be just proximal to the proximal end of the flexor retinaculum. It may be in the carpal tunnel, however, in which case, the flexor retinaculum will have to be incised

meticulously, taking care to avoid damage to the underlying median nerve. If the probe is lying in the forearm, then take great care not to damage the ulnar nerve and artery, which are very close to the flexor digitorum superficialis tendon to the little finger (see Fig. 5-91).

As is true in the case of other tendon sheath infections, a small catheter may be inserted in the distal wound to allow continuous or intermittent irrigation of the tendon sheath.

 

 

Dang

 

 

The digital nerve to the ulnar side of the little finger is in danger if the skin incision on the finger is made too far in a volar direction. The distal vessels run with the nerves.

 

How to Enlarge the Approach

 

The approach cannot be enlarged effectively by either local or extensile measures.

 

 

 

Figure 5-91 Drainage of the ulnar bursa. Make a short midline incision on the ulnar side of the little finger over the distal end of the middle phalanx. Make a second longitudinal incision over the lateral aspect of the hypothenar eminence at the level of the wrist. Pass a probe from the distal aspect to the proximal aspect,

and cut down onto the probe at its proximal end, a point that marks the proximal end of the ulnar bursa.

 

Anatomy of the Hand

Two characteristics of the normal hand reveal what happens when it is damaged:

1. The hand has a natural resting position. At rest, both the metacarpophalangeal and the interphalangeal joints normally hold a position of slight flexion. The fingers all adopt a slightly different degree of rotation, such that the volar surfaces of the terminal phalanges face progressively more toward the thumb as one moves from the index finger to the little finger. It is critical to appreciate the different degrees of rotation in the finger when assessing displacement in phalangeal or metacarpal fractures. The degree of flexion increases as one passes from the index finger to the little finger. This configuration is a result of muscle balance; if one element is deficient or absent, the resting position of the hand changes. In cases of acute trauma, a cut flexor tendon may leave a finger extended. An abnormal resting position often is indicative of tendon damage.

2. The concept of muscle balance also can be applied to chronic conditions of the hand. In patients with long-standing ulnar nerve lesions, in which the intrinsic muscles of the hand are paralyzed, the hand develops an abnormal attitude because of muscle imbalance. The intrinsic muscles normally flex the fingers at the metacarpophalangeal joints and extend them at the proximal and distal interphalangeal joints. The absence of intrinsic function leads to extension of the metacarpophalangeal joints and flexion of the proximal and distal interphalangeal joints of the affected fingers, resulting in an ulnar claw hand.

 

Palm

Skin

The skin of the palm and the palmar aspect of the fingers is a tough structure, characterized by flexure creases in the palm and fingerprints in the fingers. The skin has very little laxity because of the series of tough fibrous bands that tie it to the palmar aponeurosis. These bands divide the

subcutaneous fat into small loculi, which are capable of withstanding considerable pressure. The skin’s lack of mobility means that it is difficult to close even small defects in it without resorting to plastic procedures such as V-Y advancement flaps or skin grafting.

The blood supply of the palmar skin is extremely good, and even long, distally based flaps may survive. In an elective incision, however, the angle at the apex of a triangular flap should be more than 60 degrees, and distally based flaps should be avoided, if possible.

To avoid flexion contractures, the flexure creases should not be crossed at 90 degrees. Cutting within a flexure crease itself avoids this problem, but the wound created is difficult to close without inverting the skin edges. That is the reason that many incisions parallel natural flexure creases.

Palmar Aponeurosis

The palmar aponeurosis is a tough fibrous sheath that lies under the skin of the palm (see Fig. 5-37). It is continuous with the tendon of the palmaris longus muscle, spreading distally from the distal border of the flexor retinaculum to cover the central area of the palm between the thenar and hypothenar eminences. At the level of the distal third of the metacarpals, it divides into four bands, one for each finger. At the level of the distal palmar crease, these bands divide into two and run into the fingers to insert into the bases of the proximal phalanges and the fibrous flexor sheaths (see Fig. 5-40).

The nerves and vessels to the palm lie immediately deep to the palmar aponeurosis and actually are in contact with its deep surface. In patients with Dupuytren contracture, the palmar fascia thickens; contracted and fibrous tissue grows all around the digital nerves and vessels to enclose them.46

The fascia over the thenar and hypothenar muscles is thinner than that over the central palm because of the greater mobility required from the first and fifth digits.

The palmar aponeurosis has deep connections to the first and fifth metacarpals at its lateral and medial borders, dividing the hand into three major compartments: The thenar, hypothenar, and palmar compartments. There also are deep connections between the palmar aponeurosis and the metacarpals in the distal part of the hand (see Fig. 5-40).

Thenar Muscles

The thenar eminence consists of three short muscles: The abductor pollicis

brevis, the flexor pollicis brevis, and the opponens pollicis (see Figs. 5-40 and 5-41). All three are supplied by the median nerve via its motor branch, which enters the eminence between the short abductor and the flexor.

The flexor pollicis brevis also receives a nerve supply from the ulnar nerve to its deep head. This dual nerve supply explains the clinical observation that a complete median nerve palsy does not necessarily produce complete flattening of the thenar eminence, because the bulky deep head of the flexor pollicis brevis does not atrophy.

The three short muscles of the thumb lie in two layers. The superficial layer consists of the short abductor and the short flexor, with the abductor lying on the radial side of the flexor. The deep layer consists of the opponens pollicis, which produces rotation of the thumb metacarpal at its saddle-shaped joint with the trapezium. The ability to oppose the thumb and the other fingers is one of the major structural advantages that the human hand has over the ape hand. It is a complex movement requiring several muscles. The abductor pollicis brevis abducts the thumb, rotation is achieved by the opponens pollicis, and the movement is completed by the thumb flexors. The abductor pollicis brevis is the most important muscle in this group. Median nerve paralysis destroys opposition; the resultant hand often is known as a simian (ape-like) hand.

Hypothenar Muscles

The hypothenar eminence consists of three muscles: The abductor digiti minimi, the flexor digiti minimi brevis, and the opponens digiti minimi. These muscles (all of which are supplied by the ulnar nerve) are arranged in the same layering as are those of the thenar eminence. The superficial layer consists of the abductor and flexor, with the abductor lying on the ulnar side; the deep layer consists of the opponens digiti minimi. Together, these muscles help deepen the cup of the palm of the hand. Very little genuine opposition of the fifth finger is possible compared with that of the thumb (see Figs. 5-40 and 5-41).

Lying superficial to the muscles of the hypothenar eminence is the palmaris brevis muscle, the only muscle that is supplied by the superficial branch of the ulnar nerve.

Nerves and Vessels

The second layer of the palm consists of the superficial nerves and vessels (see Figs. 5-39 and 5-40).

The superficial palmar arch is an arterial arcade that is formed largely by the ulnar artery. The arcade is completed by the superficial palmar

branch of the radial artery, but this branch often is missing. When it is, the arch remains incomplete. Four palmar digital arteries arise from the arcade and pass distally. The most ulnar of the arteries supplies the ulnar border of the little fingers; the other three common digital arteries divide in the web space into two vessels that supply adjacent fingers.

Note that this arterial arcade is superficial to the nerves in the palm as opposed to the fingers where the arteries are the superficial structures. Also the thumb and the radial side of the index finger are not supplied by its branches.

The digital nerves lie immediately deep to the superficial palmar arch. The ulnar nerve divides into a superficial and a deep branch at the distal border of the flexor retinaculum. The superficial branch supplies the ulnar 1½ fingers with sensation. The median nerve divides into two sensory branches after giving off its motor branch to the thenar muscles. The medial branch supplies the radial side of the ring finger, the middle finger, and the ulnar side of the index finger. The lateral branch supplies the radial side of the index finger and the whole of the thumb.

Long Flexor Tendons

The third layer of structures in the palm is composed of the long flexor tendons. The tendons of the flexor digitorum superficialis muscle overlie those of the flexor digitorum profundus muscle. Each flexor profundus tendon gives rise to a lumbrical muscle, which passes along the radial side of the metacarpophalangeal joint before inserting into the extensor expansion from the dorsum of the proximal phalanx. Lumbricals that arise by two heads from adjacent profundus tendons (usually the ulnar two) are supplied by the ulnar nerve; lumbricals that arise from one tendon (usually the radial two) are supplied by the median nerve.

Deep Palmar Arch

The deep palmar arch, which is an arterial arcade, lies deep to the long flexor tendons and forms a fourth layer in the palm (see Figs. 5-41 and 5-42). The arterial arch consists of the terminal branch of the radial artery, which enters the palm by passing between the oblique and transverse heads of the adductor pollicis muscle, and the deep branch of the ulnar artery. Running with the ulnar artery is the deep branch of the ulnar nerve, which supplies all the interossei with muscular branches at this level.

Deep Muscles of the Palm

The adductor pollicis muscle and the interossei are the deepest muscles in

the palm (see Fig. 5-42).

The interossei can be divided into two groups, dorsal and palmar. The dorsal interossei arise by two heads from adjacent sides of the metacarpals and insert into the proximal phalanges so that they abduct the fingers away from the line drawn through the center of the third finger.

The three palmar interossei are much smaller. Each arises from only one metacarpal and inserts into the base of the proximal phalanx, adducting the finger toward the middle finger.

All interossei are supplied by the deep branch of the ulnar nerve. (The function of the interossei can be remembered by the mnemonics “PAD” and “DAB”: The palmar interossei adduct, and the dorsal interossei abduct.)47

Other Structures

Two structures in the palm, the deep branch of the ulnar nerve and the radial artery, have courses that do not follow the layering concept. The way in which they run through the wrist and hand ties the rest of the anatomy together.

The radial artery lies on the volar aspect of the distal radius. It reaches the dorsum of the hand under the tendons of the abductor pollicis longus muscle and the extensor pollicis brevis muscle, lying on the scaphoid bone in the anatomic snuff-box. To return to the volar aspect of the palm, it pierces the deepest layer of the palmar structures, passing between the two heads of the first dorsal interosseous muscle. At that point, it gives off two branches, the radialis indicis artery and the princeps pollicis artery, which supply the index finger and thumb, respectively. The main arterial trunk then passes between the two heads of the adductor pollicis and lies superficial to the deepest muscles as it forms the deep palmar arch.

The ulnar nerve enters the hand superficial to the flexor retinaculum within the canal of Guyon. There, it divides into superficial and deep branches (see Fig. 5-38). The superficial branch gives off digital nerves and lies in the same plane as the superficial arterial arcade. The deep branch descends through the layers of the palm, passing between the heads of origin of the opponens digiti minimi to lie on the interossei in the same plane as the radial artery. There, it supplies all the interossei, the two ulnar lumbrical muscles, both heads of the adductor pollicis muscle, the three hypothenar muscles, and the deep head of the flexor pollicis brevis muscle (see Figs. 5-41 and 5-42).

 

Dorsum of the Hand

The anatomy of the dorsum of the hand is far simpler than that of the palm. The skin is thinner than the palmar skin and is more mobile to allow for finger flexion. The subcutaneous tissue contains very little fat, but a large number of veins. Venous return runs via the dorsum of the hand because the pressure of gripping otherwise would impede it. The blood supply of the dorsal skin is not as good as that of the palmar skin, and distally based skin flaps are less likely to survive.

The backs of the radial 3½ digits are supplied by the terminal branches of the superficial radial nerve as far as the middle of the middle phalanx. The ends of these fingers are supplied by branches of the median nerve that are derived from the volar digital nerves.

The dorsal aspects of the ulnar 1½ digits are supplied by the ulnar nerve. The proximal 1½ phalanges are supplied by dorsal branches of the ulnar nerve, and the distal 1½ phalanges are supplied by volar branches of the ulnar nerve (the volar digital nerves).

The clinical importance of this arrangement is that the terminal phalanx, including the nail bed, can be anesthetized by an injection of local anesthetic around the volar digital nerves.

The only tendons of the dorsum of the hand are those of the common extensors. Just proximal to the metacarpophalangeal joint, these tendons are united by three oblique bands, which limit retraction of the tendon if it is cut. As each long extensor tendon passes over its metacarpophalangeal joint, its deepest part becomes continuous with the dorsal capsule of that joint. The tendon becomes much broader before dividing into three slips over the dorsal surface of the proximal phalanx. The central slip inserts into the base of the middle phalanx and the two marginal slips receive attachments from interossei and lumbrical tendons to form a broad extensor expansion, or hood, which overlies the metacarpal head and the proximal part of the proximal phalanx. The hood is anchored firmly on each side to the volar plate of the metacarpophalangeal joint. Each hood receives some of the insertion of each of two interossei, with the rest going to the proximal phalanx itself. The amount varies considerably from finger to finger. The entire insertion of the lumbrical tendon attaches to the extensor hood (see Figs. 5-11, 5-13, and 5-41).

Over the dorsum of the middle phalanx, the intrinsic tendons are joined to each other by transversely running fibers (the triangular ligament). Initially, the two marginal slips of the long extensor tendon pass outward from the midline to insert into the base of the distal phalanx. By inserting into this extensor expansion from the palmar side, the lumbrical and

interosseous muscles not only can abduct and adduct the fingers at the metacarpophalangeal joint, but also can flex the metacarpophalangeal joint while extending the distal and proximal interphalangeal joints. In this way, each extended finger can be flexed independently.

Disruption of the central slip of the extensor tendon and the triangular ligament may produce a flexion deformity at the proximal interphalangeal joint. The two marginal slips then pass volar to the joint and act as flexors of that joint, and the joint “buttonholes” between these two slips. This deformity is known as a boutonnière (or buttonhole) deformity.

 

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SELECTED BIBLIOGRAPHY

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MCAULIFFE JA: Combined internal and external fixation of distal radial fractures. Hand Clin. 2005;21:395–406.