Four
The Forearm
Anterior Approach to the Radius
Applied Surgical Anatomy of the Anterior Compartment of the
Forearm
Exposure of the Shaft of the Ulna
Applied Surgical Anatomy of the Approach to the Ulna
Posterior Approach to the Radius
Applied Surgical Anatomy of the Posterior Approach to the Radius
Anterior and Posterior Approaches for the Treatment of Forearm
Compartment Syndrome
Anterior Approaches for Flexor Compartment Decompression
Posterior Approach to the Forearm for Compartment Syndrome Decompression
The surgical anatomies of the two bones of the forearm differ significantly. The ulna has a subcutaneous border that extends for its entire length; the bone can be reached simply and directly without endangering other structures. In contrast, the upper two-thirds of the radius are enclosed by a sheath of muscles. All surgery in the upper third of the radius is complicated further by the posterior interosseous nerve, which winds spirally around the bone close to, if not in contact with, its periosteum.
Three surgical approaches to the forearm bones are described in this chapter, all of which allow for the complete exposure of bone. In nearly every case, only part of the approach is required. The anterior approach to the radius is one of the classic extensile approaches, relying on subperiosteal dissection for protection of the posterior interosseous nerve. The posterior approach to the radius also makes use of an internervous plane, but still requires identification and preservation of the posterior interosseous nerve. The approach to the ulna cuts directly onto its subcutaneous border. The anatomy of the anterior approach to the radius, the approach to the ulna, and the anatomy of the posterior compartment of the forearm are considered separately. Because of the critical importance of the posterior interosseous nerve, its course is described in both anatomic sections. Two surgical approaches are described at the end of the chapter for the treatment of compartment syndrome of the forearm—a condition which affects both the flexor and extensor muscular compartments of the forearm.
Anterior Approach to the Radius
The anterior approach offers an excellent, safe exposure of the radius, exposing the entire length of the bone. Although the approach can be used for exposure of the volar surface of the distal radius, alternative approaches are available for volar plating in the treatment of wrist fractures which are described on pages 196. Exposing the proximal third of the radius endangers the posterior interosseous nerve. By stripping the supinator muscle off the radius subperiosteally and using it to protect the nerve, however, the anterior approach avoids this danger. Still, great care must be taken in positioning retractors, because the nerve actually may touch the bone at the level of the distal portion of the neck of the radius, opposite the bicipital tuberosity, and posteriorly placed retractors can compress it against the bone. The approach first was described by Henry, and his name usually is associated with it.1
The uses of the anterior approach include the following:
1. Open reduction and internal fixation of fractures2
2. Bone grafting and fixation of fracture nonunions
3. Radial osteotomy
4. Biopsy and treatment of bone tumors
5. Excision of sequestra in chronic osteomyelitis
6. Anterior exposure of the bicipital tuberosity
7. Treatment of compartment syndrome
This section describes an approach that exposes the entire length of the bone. Ordinarily, only a portion of the approach is required.
Position of the Patient
Place the patient supine on the operating table, with the arm on an arm board. Place a tourniquet on the arm, but do not exsanguinate it fully before inflating the tourniquet. Venous blood left in the arm makes the vascular structures easier to identify. Finally, supinate the forearm (Fig. 41).
Landmarks and Incision
Landmarks
Palpate the biceps tendon, which is a long, taut structure that crosses the front of the elbow joint just medial to the brachioradialis muscle.
Palpate the brachioradialis, which is a fleshy muscle that arises with the extensor carpi radialis longus muscle from the lateral supracondylar ridge of the humerus. These two muscles and extensor carpi radialis brevis which arises from the common extensor origin on the front of the lateral epicondyle form a “mobile wad” of muscle that runs down the lateral aspect of the supinated forearm.
Palpate the styloid process of the radius. Note that this bony process is truly lateral when the hand is in the anatomic (supinated) position. The styloid process is the most distal part of the lateral side of the radius.
Incision
Make a straight incision from the anterior flexor crease of the elbow just lateral to the biceps tendon down to the styloid process of the radius. The length and site of the incision depends on the amount of bone that needs to be exposed and the position of the lesion to be exposed (Fig. 4-2).
Internervous Plane
Distally, the internervous plane lies between the brachioradialis muscle, which is innervated by the radial nerve, just proximal to the elbow joint, and the flexor carpi radialis muscle, which is innervated by the median nerve (Fig. 4-3). Proximally, the internervous plane lies between the brachioradialis muscle, which is innervated by the radial nerve, and the pronator teres muscle, which is innervated by the median nerve.
Figure 4-1 Position of the patient on the operating table, for the anterior approach to the radius.
Figure 4-2 Make a straight incision on the anterior part of the forearm, from the flexor crease on the lateral side of the biceps down to the styloid process of the radius.
Figure 4-3 Internervous plane. The plane lies between the brachioradialis (radial nerve) and the flexor carpi radialis (median nerve).
Superficial Surgical Dissection
Incise the deep fascia of the forearm in line with the skin incision. Identify the medial border of the brachioradialis as it runs down the forearm, and develop a plane between it and the flexor carpi radialis distally. More proximally, the plane lies between the pronator teres and brachioradialis muscles (Fig. 4-4). Note that the medial border of the brachioradialis is surprisingly far across the forearm. At the level of the elbow the brachioradialis extends almost halfway across the forearm. It is surprisingly easy to mistake the plane between brachioradialis and extensor carpi radialis for the correct intermuscular plane. The presence of the sensory branch of the radial nerve serves as a guide since this nerve runs on the underside of the brachioradialis muscle.
Figure 4-4 Incise the fascia and develop the plane between the brachioradialis and the flexor carpi radialis.
Figure 4-5 A leash of vessels from the radial artery supplies the brachioradialis. The vessels must be ligated to mobilize the brachioradialis laterally. Retract the superficial branch of the radial nerve with the brachioradialis muscle.
Begin dissection distally and work proximally. Identify the superficial radial nerve running on the undersurface of the brachioradialis and moving with it. The brachioradialis receives a number of arterial branches from the radial artery (called the recurrent radial artery) just below the elbow joint. Ligate this recurrent leash of vessels (Fig. 4-5). Take time and care to ligate these vessels and not avulse them, as avulsion is a potent cause of postoperative hematoma formation. Many vessels are present and all will need to be ligated and divided to allow the brachioradialis to be mobilized laterally. Each artery is usually accompanied by two veins
The radial artery lies beneath the brachioradialis in the middle part of the forearm; therefore, it is quite close to the medial edge of the wound. It runs with its two venae comitantes, which remain prominent if the limb is not exsanguinated before the tourniquet is applied. Often, the artery may have to be mobilized and retracted medially to achieve adequate exposure of the deeper muscular layer, particularly at the upper and lower ends of the approach (see Fig. 4-5).
The superficial radial nerve, which is a sensory nerve in the forearm, also runs under cover of the brachioradialis muscle. Preserve the nerve, because damage to it may create a painful neuroma at the operative site (see Fig. 4-5). It is retracted laterally with the brachioradialis muscle.
Deep Surgical Dissection
Proximal Third
The key to safe exposure of the proximal radius in fixation of very high fractures is the biceps tendon. Follow the biceps tendon to its insertion into the bicipital tuberosity of the radius. Just lateral to the tendon is a small bursa; incise the bursa to gain access to the proximal part of the shaft of the radius. Because the radial artery lies superficial and just medial to the tendon at this point, deepen the wound on the lateral side of the biceps tendon (Fig. 4-6).
The proximal third of the radius is covered by the supinator muscle, through which the posterior interosseous nerve passes on its way to the posterior compartment of the forearm.
The posterior interosseous nerve is the single most important structure left vulnerable by this approach. To displace the nerve laterally and posteriorly (away from the surgical area), fully supinate the forearm, exposing, at the same time, the insertion of the supinator muscle into the anterior aspect of the radius (Fig. 4-7).
Next, incise the supinator muscle along the line of its broad insertion. Ensure that the muscle is detached by dividing its insertion and not by splitting the muscle. Continue subperiosteal dissection laterally, stripping the muscle off the bone (see Fig. 4-7). This is one of the rare examples where the safety obtained by staying in a subperiosteal plane outweighs the vascular damage to the bone caused by stripping off periosteum. Lateral retraction of the muscle lifts the posterior interosseous nerve clear of the operative field, but be careful! Excessive retraction may cause a neurapraxia of the nerve, and it recovers very slowly, taking up to 6 to 9 months. Finally, do not place retractors on the posterior surface of the radial neck, because they may compress the posterior interosseous nerve against the bone in patients whose nerve comes into direct contact with the posterior aspect of the radial neck (about 25% of all patients).3
Figure 4-6 Deep to the brachioradialis and the flexor carpi radialis are the supinator muscle, the pronator teres, the flexor digitorum superficialis, and, most distally, the pronator quadratus.
Figure 4-7 With the patient’s arm in the supinated position, resect the insertion of the supinator. Reflect the muscle laterally. Leave the posterior interosseous nerve in the muscle’s substance. The radial nerve enters the supinator through the arcade of Frohse (inset). Turning the forearm upward moves the nerve laterally, away from the operative field. The insertion of the supinator muscle is easier to identify if the surgeon stays lateral to the biceps tendon and locates the bursa between it and the supinator.
Figure 4-8 Turn the arm downward to identify the pronator teres muscle. Resect it along its insertion on the lateral aspect of the radius.
Middle Third
The anterior aspect of the middle third of the radius is covered by the pronator teres and flexor digitorum superficialis muscles. To reach the anterior surface of the bone, pronate the arm so that the insertion of the pronator teres onto the lateral aspect of the radius is exposed (Fig. 4-8; see Fig. 4-6). Detach this insertion from the bone and strip the muscle off medially. Preserve as much soft tissue as you can compatible with accurate reduction and fixation of the fracture. This maneuver partially detaches the origin of the flexor digitorum superficialis from the anterior aspect of the radius as well (Fig. 4-9).
Distal Third
Two muscles, the flexor pollicis longus and the pronator quadratus, arise from the anterior aspect of the distal third of the radius. To reach bone, partially supinate the forearm and incise the periosteum of the lateral aspect of the radius lateral to the pronator quadratus and the flexor pollicis longus. Then, continue the dissection distally, retracting the two muscles medially and lifting them off the radius (Fig. 4-10). Controversy exists as whether detaching the origin of pronator quadratus gives superior clinical results to just dividing the muscle in the line of the skin incision. Detaching the muscle would appear to give a better prospect of repair during closure and to provide a soft tissue pad between the superficial tendons and a volar plate. This is however as yet unproven.4
Figure 4-9 Continue dissection distally to uncover the distal part of the radius. Leave the periosteum intact.
Figure 4-10 With the arm in partial supination, remove the flexor pollicis longus and the pronator quadratus from the bone to expose the entire radius from its proximal to distal end.
Dangers
Nerves
The posterior interosseous nerve is vulnerable as it winds around the neck of the radius within the substance of the supinator muscle. The key to ensuring its safety is to detach correctly the insertion of the supinator muscle from the radius. The insertion of the muscle is exposed completely only when the arm is supinated fully. In cases where there are extensive contusions in the area begin by identifying the tendon of biceps which is nearly always easy to do. Follow the tendon distally until the bursa is entered. This in turn will lead directly onto the surface of the bone. The origin of the supinator can then be found usually by gently wiping the surface of the muscle with a damp swab. Once the subperiosteal dissection is begun, the nerve is comparatively safe, but overzealous retraction still can lead to a neurapraxia (see Figs. 4-7, inset, and 4-13).
The superficial radial nerve runs down the forearm under the brachioradialis muscle. It becomes vulnerable when the “mobile wad” of three muscles is mobilized and retracted laterally (see Fig. 4-5). The superficial radial nerve is vulnerable to neurapraxia if it is retracted vigorously. Take great care, therefore, when retracting the nerve and warn your patients preoperatively that temporary paresthesia in the distribution of the superficial branch of the radial nerve may occur in the early postoperative phase.
Vessels
The radial artery runs down the middle of the forearm under the brachioradialis muscle. It is vulnerable twice during the anterior approach to the radius:
1. During mobilization of the brachioradialis. Protection depends onrecognizing the artery. Its two accompanying venae comitantes are the best surgical guide, because the artery is surprisingly small after a tourniquet has been used (see Fig. 4-5).
2. In the proximal end of the wound, as the artery passes to the medial sideof the biceps tendon. Damage to the artery at that level can be avoided by remaining lateral to the tendon (see Fig. 4-13).
The recurrent radial arteries are a leash of vessels that arise from the radial artery just below the elbow joint. They consist of two groups, anterior and posterior, which pass in front of and behind the superficial radial nerve, respectively, before entering the brachioradialis muscle. They must be ligated to allow mobilization of both the artery and the nerve (see Figs. 4-9 and 4-12).
How to Enlarge the Approach
The anterior approach provides complete access to the entire length of the radius. The approach can be extended distally to expose the wrist joint.5 Although it can be extended into an anterolateral approach to the elbow and humerus, such extension rarely is required.
Applied Surgical Anatomy of the Anterior Compartment of the Forearm
Overview
Muscles
Two muscle groups form the musculature of the anterior aspect of the forearm: The mobile wad of three (the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis), which is supplied by the radial nerve, forms the lateral border of the supinated forearm; and the flexor-pronator muscles, which are supplied by the median and ulnar nerves, comprise the rest.
The flexor-pronator group is arranged in three layers. In the superficial layer, four muscles arise from the common flexor origin on the medial humeral epicondyle and fan out across the forearm. They are easy to remember by the following simple maneuver. Place the butt of the opposite hand over the medial epicondyle, with the palm on the anterior surface of the forearm: The thumb points in the direction of the pronator teres, the index finger represents the flexor carpi radialis, the middle finger represents the palmaris longus, and the ring finger represents the flexor carpi ulnaris (Figs. 4-11 and 4-12).
The middle layer consists of the flexor digitorum superficialis (Fig. 413).
The deep layer comprises three muscles: The flexor digitorum profundus, the flexor pollicis longus, and the pronator quadratus. (A fourth deep muscle, the supinator, is critical to the surgical anatomy of the area, but is not strictly a flexor muscle [Fig. 4-14].)
The keys to the surgical anatomy of the anterior aspect of the forearm are the following three practical internervous planes that are used in operative approaches:
1. Between the radial and median nerves: A dissection between the brachioradialis muscle, the most medial of the three muscles forming the “mobile wad of three” (which is supplied by the radial nerve), and the flexor carpi radialis and pronator teres muscles, the most lateral of the flexor-pronator group (which are supplied by the median nerve; see Fig. 4-3).
Figure 4-11 Superficial layer of the forearm muscles and vessels.
Figure 4-12 The superficial layer of the forearm has been resected, revealing the vessels and nerves. The median nerve pierces the gap between the two heads of the pronator teres. Note the leash of vessels of the radial artery and the recurrent radial artery.
Figure 4-13 The middle layer of the forearm, with the superficial branch of the radial nerve. In the proximal part of the wound, the median nerve enters the undersurface of the superficialis.
Flexor Carpi Radialis. Origin. Common flexor origin on medial epicondyle of humerus. Insertion. Bases of second and third metacarpals. Action. Flexor and radial deviator of wrist. Nerve supply. Median nerve.
Figure 4-14 The deep layer of the forearm. The ulnar nerve and artery and the median nerve lie on the flexor digitorum profundus. Note the position of the anterior interosseous nerve and artery.
2. Between the median and ulnar nerves: A dissection between the flexorcarpi ulnaris muscle (which is supplied by the ulnar nerve) and the flexor digitorum superficialis muscle, the most medial of the flexor muscles (which is supplied by the median nerve; see Fig. 5-29).
3. Between the ulnar and posterior interosseous nerves: A dissectionbetween the flexor carpi ulnaris muscle (which is supplied by the ulnar nerve) and the extensor carpi ulnaris muscle (which is supplied by the posterior interosseous nerve; see Fig. 4-19).
4. The first of these planes is used in the anterior approach to the radius,the second exposes the ulnar nerve in the forearm, and the third is used for exposure of the ulna.
Nerves and Vessels
The neurovascular architecture of the anterior aspect of the forearm is relatively simple: The forearm is “framed” by its nerves. The superficial radial nerve runs down the radial aspect of the forearm, with the radial artery lying on its medial side in the distal half of the forearm (see Fig. 413). The ulnar nerve runs down the ulnar side of the forearm, with the ulnar artery lying on its lateral side in the distal half of the forearm. The median nerve runs down the middle of the forearm (see Fig. 4-14).
Both the radial and the ulnar arteries are arteries of transit in the forearm; they both are branches of the brachial artery. Because the brachial artery lies in the middle of the anterior aspect of the elbow, with the median nerve lying on its medial side, the ulnar artery and median nerve must cross in the upper forearm, with the nerve superficial to the artery; this crossing occurs at the level of the musculotendinous region of the pronator teres muscle (see Fig. 4-13). The anterior interosseous nerve (which is a branch of the median nerve) and the anterior interosseous artery (which is a branch of the common interosseous artery, which itself is a branch of the ulnar artery) also run down the middle of the forearm, but deeper than the median nerve (see Fig. 4-14).
Incision
Because the incision runs transversely across the lines of cleavage in the forearm, the resultant scar may be broad. Making the incision as a series of gentle curves brings the skin incision closer to the lines of cleavage in the forearm. Such an incision has the effect of reducing tension on the subsequent skin repair.
Superficial Surgical Dissection and Its Dangers
Muscles
Superficial surgical dissection opens the plane between the mobile wad of three muscles (the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis) and the pronator teres muscle proximally and flexor carpi radialis muscle distally (see Fig. 4-11).
The mobile wad of three muscles, on the radial side of the forearm, is supplied by the radial nerve. All three muscles take some of their origin from the common extensor origin on the lateral epicondyle of the humerus (see Fig. 4-13).
The brachioradialis pronates the forearm when it is supinated and supinates it when it is pronated. Therefore, it may act as a deforming force in distal radial fractures if the forearm is immobilized in either full pronation or full supination after reduction of the fracture. Its action is one reason for immobilizing distal radial fractures with the forearm in the neutral position.
The brachioradialis is the only muscle in the body to take origin from the distal end of one bone and insert onto the distal end of another (Fig. 415; see Fig. 4-11).
During recovery from high radial nerve palsy, the extensor carpi radialis longus is one of the first muscles to be reinnervated. If the patient recovering from a high radial nerve palsy is asked to extend the wrist, the wrist extends with radial deviation, because the balancing muscle, the extensor carpi ulnaris receives its nerve supply from the posterior interosseous nerve further distally. Reinnervation of the brachioradialis, however, probably is the best way to diagnose both clinically and electrically (by electromyographic studies) a recovering high radial nerve palsy (see Figs. 4-12 and 4-22).
The extensor carpi radialis brevis muscle is a wrist extensor that deviates the wrist neither toward the radius nor toward the ulna. It may be involved in tennis elbow—lateral epicondylitis.
Nerves and Vessels
Palsies of the posterior interosseous nerve caused by compression of the nerve by the tendinous origin of the extensor carpi radialis brevis muscle have been described.
Two structures that lie under the brachioradialis muscle must be preserved during superficial surgical dissection:
1. The radial artery originates from the brachial artery in the cubital fossa. Proximally, it lies just medial to the biceps tendon in a somewhat superficial position. The radial artery angles across the arm as it descends, lying on the supinator, the pronator teres, the origin of the flexor pollicis longus, and the lower part of the anterior surface of the radius, where it can be palpated easily (see Fig. 4-13).
2. The superficial radial nerve is purely sensory in the forearm. It runs along the lateral side, crossing the supinator, the pronator teres, and the flexor digitorum superficialis. Damage to the nerve in the forearm produces an area of diminished sensation on the dorsoradial aspect of the hand. The most important problem associated with such damage is not the sensory loss, however, but the painful neuroma that may result. The nerve runs lateral to the radial artery when the two are together (see Figs. 4-13 and 4-32).
Deep Surgical Dissection and Its Dangers
Five muscles must be detached from the radius to expose fully the anterior aspect of the bone. From proximal to distal, they are as follows:
1. The supinator
2. The pronator teres
3. The flexor digitorum superficialis
4. The flexor pollicis longus
5. The pronator quadratus
The nerve supply of the supinator muscle, the posterior interosseous nerve, passes through a fibrous arch known as the arcade of Frohse as it enters the muscle (see Figs. 4-12 and 4-13).6 The arch is formed by the thickened edge of the superficial head of the supinator. Compression of the nerve at that point produces paralysis or dysfunction of all the extensor muscles of the forearm, fingers, and thumb, a lesion that may be incomplete. Compression at the arcade of Frohse is one of the causes of a posterior interosseous nerve entrapment syndrome7 and can be relieved by incising the fibrous arch.8–11 It also is a cause of pain restricted to this area, which may present as a resistant “tennis elbow” (see Fig. 4-13).12
The nerve supply of the pronator teres, the median nerve, enters the forearm between the muscle’s two heads of origin (see Fig. 4-12). The great variations that occur in the site, size, and quality of the ulnar head of the muscle sometimes cause the nerve to become trapped as it traverses the muscle, producing the pronator syndrome, which mimics the carpal tunnel syndrome, but includes pain and paresthesia to the proximal end of the volar aspect of the forearm.13,14 Understandably, the syndrome occurs when the muscle contracts and further compresses the nerve. In this syndrome, the intrinsic muscles of the thumb become weak, but the muscles that are innervated by the anterior interosseous nerve (the flexor pollicis longus, the flexor profundus to the index and middle fingers, and the pronator quadratus) are spared (see Fig. 4-12).
The median nerve passes under the fibrous arch of origin of the flexor digitorum superficialis. It may be compressed by a thickened arch, producing pain or a median nerve palsy (see Fig. 4-13).15 The tendons of the muscle form well above the wrist. Functionally, it is four separate muscles; it can flex each finger independently, in contrast to the mass action of the flexor digitorum profundus.
Part of the origin of the flexor digitorum superficialis may have to be detached to expose the anterior part of the shaft of the radius (see Figs. 413 and 4-15).
The origin of the flexor pollicis longus, which is the sole long flexor of the thumb, must be stripped off the radius for the bone to be accessible (see Figs. 4-14 and 4-15).
The insertion of the pronator quadratus must be stripped off to expose the distal fourth of the radius (see Fig. 4-15). Because the muscle is relaxed totally when the forearm is pronated fully, some authors suggest that distal radial fractures should be immobilized in pronation. Clearly, however, the pronator quadratus is not the only possible deforming force on the distal radius; the best position for immobilizing reduced fractures of the distal radius still is a matter of debate and many authors now favor nonoperative treatment of such fractures by reduction followed by immobilization in supination (Fig. 4-16).16
Figure 4-15 The origins and insertions of the muscles of the forearm. Note the anterior interosseous artery lying on the interosseous membrane.
Brachioradialis. Origin. Upper two-thirds of lateral supracondylar ridge of humerus. Insertion. Styloid process of radius. Action. Flexor of elbow. Pronator and supinator of forearm. Nerve supply. Radial nerve.
Flexor Digitorum Superficialis. Origin. Medial epicondyle of humerus, medial ligament of elbow, medial border of coronoid process of ulna, fibrous arch connecting coronoid process of ulna with anterior oblique line of radius. Insertion. Volar aspect of middle phalanges of fingers. Action.
Flexor of proximal interphalangeal joints, metacarpophalangeal joints, and wrist joint. Nerve supply. Median nerve.
Flexor Pollicis Longus. Origin. Middle part of anterior surface of radius. Insertion. Distal phalanx of thumb. Action. Main flexor of thumb. Nerve supply. Anterior interosseous nerve.
Pronator Quadratus. Origin. Lower fourth of volar surface of ulna. Insertion. Lower fourth of lateral aspect of radius. Action. Weak pronator of forearm. Nerve supply. Anterior interosseous nerve.
Palmaris Longus. Origin. Common flexor origin on humerus. Insertion. Palmar aponeurosis. Action. Weak flexor of wrist. Nerve supply. Median nerve.
Flexor Digitorum Profundus. Origin. Upper three-fourths of anterior surface of ulna. Insertion. Distal phalanges of fingers. Action. Flexor of distal interphalangeal joints, proximal interphalangeal joints, metacarpophalangeal joints, and wrist joint. Nerve supply. Dual nerve supply from the anterior interosseous branch of the median nerve and the ulnar nerve.
Flexor Carpi Ulnaris. Origin. From two heads. Humeral head: from common flexor origin on medial epicondyle of humerus. Ulnar head: from medial border of olecranon and upper three-fourths of subcutaneous border of ulna. Insertion. Hamate and fifth metacarpal. Action. Flexor and ulnar deviator of wrist. Also weak flexor of elbow. Nerve supply. Ulnar nerve.
Dangers
Nerves
The posterior interosseous nerve is the motor nerve of the extensor compartment of the forearm. A branch of the radial nerve, it passes between the two heads of origin of the supinator muscle and actually may come in direct contact with the periosteum of the neck of the radius. At that point, it may be trapped beneath incorrectly positioned plates or retractors. After emerging from the supinator muscle, the nerve passes down over the origin of the abductor pollicis longus muscle to reach the interosseous membrane. It continues distally on the interosseous membrane to the wrist joint, which it supplies with some sensory branches. The nerve supplies the muscles that arise from the common extensor origin and the deep muscles of the extensor compartment of the forearm.
The posterior interosseous nerve is vulnerable during all approaches to the upper third of the radial shaft. Although the nerve can be protected if the insertion of the supinator is detached and the muscle is stripped off the bone subperiosteally, it can be argued that the only certain protection as the upper third of the radius is plated comes from identifying and preserving the nerve via a posterior approach (see Figs. 4-32 and 4-33).
Figure 4-16 The bones of the forearm.
Proximally, the median nerve usually passes between the heads of the pronator teres muscle, whereas the ulnar artery passes deep to both the heads. Distal to the pronator teres, the median nerve joins the ulnar artery and passes beneath the fibrous arch of origin of the flexor digitorum superficialis muscle. Then, it runs down the flexor aspect of the forearm, roughly in the midline (see Figs. 4-13 and 4-14).
Because of its proximity to the flexor digitorum superficialis muscle, the median nerve sometimes is mistaken for the superficial tendon to the index finger. To differentiate nerve from tendon, try to find an artery on the structure in question: The median nerve has the median artery running along its surface. The artery, derived from the anterior interosseous artery, is the original fetal axial artery (see Fig. 4-14).
Special Anatomic Points
The main surgical use of the palmaris longus muscle is as a graft for tendon repairs. Because it is absent in 10% of the population, it must be identified in the conscious patient before surgery is undertaken. To find it, instruct the patient to touch the thumb and little fingers together while flexing the wrist against resistance. Then, palpate the tendon, which stands out prominently in the forearm (see Fig. 4-11).
Note that the median nerve is immediately below the palmaris longus at the wrist. In the patient with an absent palmaris longus, the nerve actually may be mistaken for the tendon (see Fig. 4-11).
The tendons of the flexor digitorum profundus arise at or below the level of the wrist joint. Therefore, contraction of the muscle produces movement in all four tendons, making it a mass action muscle that is used mainly for power grip.
The anterior interosseous nerve arises from the median nerve shortly after the median nerve enters the forearm; the two lie under the tendinous origin of the superficial head of the pronator teres (see Figs. 4-12 and 413). The anterior interosseous nerve may be compressed at this point, producing the anterior interosseous nerve syndrome: Paralysis of the flexor pollicis longus and flexor profundus tendons to the index and middle fingers, as well as of the pronator quadratus muscle.17–19
Exposure of the Shaft of the Ulna
Exposing the shaft of the ulna is the simplest of all forearm approaches, uncovering the entire length of bone. The exposure uses the internervous plane between the extensor carpi ulnaris and flexor carpi ulnaris muscles. Both muscles attach by a shared aponeurosis into the subcutaneous border of the ulna, the border of bone that is exposed initially during the approach.
Because the two muscles that form the boundaries of the internervous plane share a common aponeurosis, they cannot be separated at their origin, and the plane is difficult to define. Fibers of the extensor carpi ulnaris usually have to be detached from the aponeurosis.
The uses of the approach include the following:
1. Open reduction and internal fixation of ulnar fractures
2. Treatment of delayed union or nonunion of ulnar fractures
3. Osteotomy of the ulna
4. Treatment of chronic osteomyelitis
5. Treatment of the fibrous anlage of the ulna in cases of ulnar clubhand2
6. Ulnar lengthening (in Kienböck disease)20
7. Ulnar shortening (in cases of distal radial malunion)
Position of the Patient
Place the patient supine on the operating table with the arm placed across the chest to expose the subcutaneous border of the ulna. Exsanguinate the limb either by elevating it for 3 to 5 minutes or by applying a soft rubber bandage and then inflate a tourniquet (Fig. 4-17).
Alternatively, flex the elbow to 90 degrees while resting it on the operating table.
Landmarks and Incision
Landmarks
The subcutaneous border of the ulna can be palpated along its entire length. It is felt most easily in the proximal and distal thirds of the bone.
Incision
Make a linear, longitudinal incision over the subcutaneous border of the ulna. The length of the incision depends on the amount of bone that is to be exposed. In cases of fracture, center the incision over the fracture site (Fig. 4-18).
Internervous Plane
The internervous plane lies between the extensor carpi ulnaris muscle, which is supplied by the posterior interosseous nerve, and the flexor carpi ulnaris muscle, which is supplied by the ulnar nerve (Fig. 4-19).
Superficial Surgical Dissection
Beginning in the distal half of the incision, incise the deep fascia along the same line as the skin incision; continue the dissection down to the subcutaneous border of the ulna (Fig. 4-20). Even though the bone feels subcutaneous in its middle third, some fibers of the extensor carpi ulnaris muscle nearly always have to be divided to reach the bone.
Figure 4-17 Position of the patient on the operating table, for exposure of the shaft of the ulna.
Figure 4-18 Incision for ulnar exposure. Make a longitudinal incision over the subcutaneous border of the ulna.
In the region of the olecranon, the flexor carpi ulnaris and anconeus muscles run along the plane of dissection. The plane still is an internervous plane, because the anconeus is supplied by the radial nerve and the flexor carpi ulnaris is supplied by the ulnar nerve.
Deep Surgical Dissection
In cases in which trauma has split the periosteum, providing access to the fracture, continue the dissection in the epiperiosteal plane to expose either the flexor or extensor aspects of the bone as needed. Keep soft tissue stripping to a minimum to preserve blood supply to the fracture (Fig. 421).
Figure 4-19 The internervous plane lies between the extensor carpi ulnaris (posterior interosseous nerve) and the flexor carpi ulnaris (ulnar nerve).
Figure 4-20 Make an incision through the fascia onto the subcutaneous border of the ulna.
Figure 4-21 A: Lift the periosteum longitudinally on the posterior aspect of the ulna, both radially and medially, to expose the entire posterior length of the ulna. B: Epiperiosteal dissection around the ulna is safe; the muscle masses on each side protect the vital structures.
Figure 4-22 The ulnar nerve is vulnerable during the most proximal dissections of the ulna. It must be identified before muscle is stripped from bone in the proximal fifth.
In the proximal fifth of the ulna, part of the insertion of the triceps tendon will need to be detached to gain access to the bone. This insertion is very broad and long, and it blends in with the periosteum of the subcutaneous surface of the olecranon.
Dangers
Nerves
The ulnar nerve, which travels down the forearm under the flexor carpi ulnaris, lies on the flexor digitorum profundus. The nerve is safe as long as the flexor carpi ulnaris is stripped off the ulna epiperiosteally. If the dissection strays into the substance of the muscle, however, the nerve may be damaged. Because the nerve is most vulnerable during very proximal dissections, it should be identified as it passes through the two heads of the flexor carpi ulnaris before the muscle is stripped off the proximal fifth of the bone (Fig. 4-22).
Vessels
The ulnar artery travels down the forearm with the ulnar nerve, lying on its radial side. Therefore, it also is vulnerable when dissection of the flexor carpi ulnaris is not carried out epiperiosteally (see Fig. 4-21B).
How to Enlarge the Approach
Local Measures
The approach described provides excellent exposure of the entire bone and cannot be enlarged usefully by local measures.
Extensile Measures
The approach cannot be extended usefully distally. It can be extended over the olecranon and up the back of the arm, however, either to expose the elbow joint through an olecranon osteotomy or to approach the posterior aspect of the distal two-thirds of the humerus.
Applied Surgical Anatomy of the Approach to the Ulna
Anatomy of the Surgical Dissection and Its Dangers
Two muscles are separated in the approach to the ulna: The flexor carpi ulnaris (which is supplied by the ulnar nerve) and the extensor carpi ulnaris (which is supplied by the posterior interosseous nerve; see Fig. 422).
The muscular branch of the ulnar nerve, which innervates the flexor carpi ulnaris, effectively tethers the nerve, preventing further distal mobilization during decompression at the elbow. Compression lesions of
the nerve have been described (see Fig. 3-49).21,22
The extensor carpi ulnaris is the most medial of the muscles that are innervated by the posterior interosseous nerve. Thus, it forms one border of the internervous plane between the muscles that are innervated by the posterior interosseous nerve and those that are innervated by the ulnar nerve, the most medial of which is the flexor carpi ulnaris (see Fig. 4-19).
The ulnar nerve runs down the medial side of the forearm between the flexor digitorum profundus and the flexor digitorum superficialis, and under the flexor carpi ulnaris. In the forearm, it supplies the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus (see Fig. 4-14).
The ulnar artery is a terminal branch of the brachial artery. It usually enters the forearm deep to the deep head of the pronator teres before angling medially across the forearm and passing under the fibrous arch of the flexor digitorum superficialis, where it runs just deep to the median nerve (see Figs. 4-12 to 4-14). In the distal two-thirds of the forearm, the artery runs on the lateral side of the ulnar nerve, lying on the flexor digitorum profundus and under the flexor carpi ulnaris. The artery has one major branch in the forearm, the common interosseous artery, which divides almost immediately into two tributaries, the anterior interosseous artery (which runs down the forearm in the midline, lying on the interosseous membrane) and the posterior interosseous artery (which pierces the interosseous membrane, running down the forearm in its posterior compartment; see Fig. 4-14).
The ulnar nerve and ulnar artery may be endangered during superficial dissection if the dissection strays to the flexor side of the bone.
Posterior Approach to the Radius
The posterior approach to the radius provides good access to the entire dorsal aspect of the radial shaft.23 The principal aim of the approach is to isolate and retract the posterior interosseous nerve before exposing the most proximal parts of the radial shaft, keeping the nerve under direct observation during all stages of the subsequent procedure and protecting it from damage. The uses of the posterior approach include the following:
1. Open reduction and internal fixation of radial fractures (the approachprovides access to the extensor side of the bone; this is the tensile side of the bone, where plates should be placed, if possible)
2. Treatment of delayed union or nonunion of fractures of the radius
3. Access to the posterior interosseous nerve; decompression of the nerveas it passes through the arcade of Frohse for nerve paralysis or resistant tennis elbow11
4. Radial osteotomy
5. Treatment of chronic osteomyelitis of the radius
6. Biopsy and treatment of bone tumors
Position of the Patient
Place the patient in one of two positions:
1. Place the patient supine on the operating table, with the arm on an armboard. Pronate the patient’s arm to expose the extensor compartment of the forearm.
2. Place the patient’s arm across the chest to expose its extensorcompartment (Fig. 4-23). If the ulna must be approached as well as the radius, this position will allow easier access to the ulna through a separate incision.
In both positions, exsanguinate the limb by elevating the arm for 3 to 5 minutes or by applying a soft rubber bandage or exsanguinator. Then, inflate a tourniquet.
Landmarks and Incision
Landmarks
Palpate the lateral epicondyle of the humerus just lateral to the olecranon process on the distal humerus. It is a prominent bony landmark, but is somewhat smaller and less defined than the medial epicondyle of the humerus.
Figure 4-23 Position of the patient’s arm on the operating table, for the posterior approach to the radius.
Lister tubercle (the dorsoradial tubercle) lies about a third of the way across the dorsum of the wrist from the styloid process of the radius. It feels like a small, longitudinal bony prominence or nodule.
Incision
Make a straight incision, extending from a point anterior to the lateral epicondyle of the humerus (along the dorsal aspect of the forearm) to a point just distal to the ulnar side of Lister tubercle at the wrist (Fig. 4-24).
Normally, only part of this incision is required for any given operation. In cases of fracture, the incision should be centered over the fracture site. Use of an image intensifier may allow more accurate placement of the incision.
Internervous Plane
No true internervous plane exists in this approach. Proximally, the intermuscular plane lies between the extensor carpi radialis brevis muscle (which is supplied by the posterior interosseous nerve proximal to the supinator muscle) and the extensor digitorum communis muscle (which is supplied by the posterior interosseous nerve on the back of the forearm); (Fig. 4-25). The common aponeurosis of these muscles is the cleavage plane.
Distally, the plane lies between the extensor carpi radialis brevis muscle (which is supplied by the posterior interosseous nerve) and the extensor pollicis longus muscle (which is supplied by the posterior interosseous nerve).
Superficial Surgical Dissection
Incise the deep fascia in line with the skin incision and identify the space between the extensor carpi radialis brevis and the extensor digitorum communis. This plane is more obvious distally, where the abductor pollicis longus and the extensor pollicis brevis emerge from between the two muscles. Proximally, the extensor carpi radialis brevis and the extensor digitorum communis share a common aponeurosis (Figs. 4-26 and 4-27).
Continue the dissection proximally, separating the two muscles to reveal the upper third of the shaft of the radius, which is covered by the enveloping supinator muscle.
Below the abductor pollicis longus and the extensor pollicis brevis, identify the intermuscular plane between the extensor carpi radialis brevis and the extensor pollicis longus. Separating the two muscles exposes the lateral aspect of the shaft of the radius (Figs. 4-28 and 4-29).
Deep Surgical Dissection
Proximal Third
The supinator muscle cloaks the dorsal aspect of the upper third of the radius; the posterior interosseous nerve runs within its substance between the superficial and deep heads. The nerve emerges from between the superficial and deep heads of the supinator muscle about 1 cm proximal to the distal edge of the muscle. At this point, it divides into branches that supply the extensors of the wrist, fingers, and thumb (see Fig. 4-29).
Figure 4-24 The long incision extends from just anterior to the lateral epicondyle of the humerus to just distal to the ulnar side of Lister tubercle at the wrist.
Figure 4-25 The intermuscular plane lies between the extensor carpi radialis brevis (posterior interosseous nerve) and the extensor digitorum communis (posterior interosseous nerve).
Figure 4-26 Incise the deep fascia and identify the space between the extensor carpi radialis brevis and the extensor digitorum communis. The identification is easier distally.
Figure 4-27 The interval between the extensor carpi radialis brevis and the extensor digitorum communis.
Figure 4-28 The supinator muscle, beneath the extensor carpi radialis brevis and the extensor digitorum communis.
Figure 4-29 The supinator cloaks the upper third of the radius; the posterior interosseous nerve runs through its substance. The nerve must be protected and identified as it traverses the muscle. The interosseous nerve is seen in the substance of the supinator (inset).
Two methods exist for successfully identifying and preserving this nerve as it traverses the muscle.
1. Proximal to distal (see Fig. 4-29, inset). Detach the origin of the extensor carpi radialis brevis and part of the origin of the extensor carpi radialis longus from the lateral epicondyle and retract these two muscles laterally. Next, identify the posterior interosseous nerve proximal to the proximal end of the supinator muscle by palpating the nerve. Now, carefully dissect the nerve out through the substance of the supinator, in a proximal to distal direction, taking great care to preserve the multiple motor branches to the muscle itself.
2. Distal to proximal (see Fig. 4-29). Identify the nerve as it emerges from the supinator. Note that it emerges about 1 cm proximal to the distal end of the muscle. Now, follow the nerve proximally through the substance of the muscle, taking care to preserve all muscular branches.
When the nerve has been identified and preserved successfully, fully supinate the arm to bring the anterior surface of the radius into view. Detach the insertion of the supinator muscle from the anterior aspect of the radius. Strip the supinator off the bone subperiosteally to expose the proximal third of the shaft of the radius (Fig. 4-30).
Middle Third
Two muscles, the abductor pollicis longus and the extensor pollicis brevis, blanket this approach as they cross the dorsal aspect of the radius before heading distally and radially across the middle third of the radius. To retract them off the bone, make an incision along their superior and inferior borders. Then, they can be separated easily from the underlying radius and retracted either distally or proximally, depending on the exposure that is required (see Fig. 4-30). Plates can be slid underneath these muscles if required for fixation. Plates placed in this position are on the tension side of the bone which is biomechanically the best place but irritation of the overlying tendons may be a problem.
Figure 4-30 Detach the insertion of the supinator from the anterior aspect of the radius, with the arm in full supination to bring the insertion of the supinator into view and to move the posterior interosseous nerve away from the area of incision. Along the distal third of the bone, the extensor carpi radialis brevis has been separated from the extensor pollicis longus, uncovering the lateral border of the radius.
Distal Third
Separating the extensor carpi radialis brevis from the extensor pollicis longus already has led directly onto the lateral border of the radius (see Fig. 4-30).
Dangers
There are two ways in which to preserve the critical posterior interosseous nerve, which is the key to this dissection:
1. Identification of the nerve. In 25% of patients, the posterior interosseous nerve actually touches the dorsal aspect of the radius just below the bicipital tuberosity24; plates placed high on the dorsal surface of the radius may trap the nerve underneath.25 Identifying and preserving the nerve in the supinator muscle is the only means of ensuring that it will not be trapped beneath any plate that is applied for a radial fracture (see Fig. 4-29).
2. Protecting the nerve with the supinator muscle. Strip the supinator off the anterior aspect of the radius and retract it radially, with the nerve still enclosed in its substance. This technique often is used in the anterior approach to the radius, exposing the anterior surface of the bone. The dorsal aspect of the radius can be exposed in the same way, but because the posterior interosseous nerve actually touches the periosteum in one of four patients, the safest procedure is to dissect the nerve out fully before stripping the muscle from the bone (see Fig. 4-30). Also be aware that the position of the nerve changes with the type of trauma affecting the proximal radius.26
How to Enlarge the Approach
Local Measures
To widen the plane between the extensor carpi radialis brevis and extensor digitorum communis muscles, detach the origin of the extensor carpi radialis brevis from the common extensor origin on the lateral epicondyle of the humerus.
Extensile Measures
The approach can be extended to the dorsal side of the wrist (see Dorsal Approach to the Wrist in Chapter 5). It can be extended proximally to expose the lateral epicondyle of the humerus (see Lateral Approach to the Distal Humerus in Chapter 2). These extensions, however, rarely are required.
Applied Surgical Anatomy of the Posterior Approach to the Radius
Overview
Twelve muscles appear on the dorsal aspect of the forearm. They are divided into three groups, as follows:
1. The mobile wad of three (the brachioradialis, extensor carpi radialis longus, and extensor carpi radialis brevis) runs along the lateral side of the forearm. These three muscles arise from a continuous line on the lateral supracondylar ridge and lateral epicondyle of the humerus.
2. The four superficial extensor muscles fan out from the lateral epicondyle of the humerus. From the ulnar to the radial side of the forearm, they consist of the anconeus, the extensor carpi ulnaris, the extensor digiti minimi, and the extensor digitorum communis (Figs. 4-31 and 4-32). One internervous plane exists in this layer of musculature: Between the extensor carpi ulnaris muscle (which is supplied by the posterior interosseous nerve) and the flexor carpi ulnaris muscle (which is supplied by the ulnar nerve) on the ulnar side (see Fig. 4-19). The intermuscular plane between the extensor carpi radialis brevis muscle27 (which is supplied by the posterior interosseous nerve proximal to the supinator muscle) and the extensor digitorum communis muscle (which is supplied by the posterior interosseous nerve in the forearm) is utilized in the posterior approach to the radius. The plane is safe to use in the forearm because the extensor carpi radialis brevis receives its nerve supply well proximal to the dissection (see Fig. 4-25).
3. Of the five deep muscles, three (the abductor pollicis longus, the extensor pollicis brevis, and the extensor pollicis longus) supply the thumb. The three cross the forearm obliquely from the ulnar to the radial side, and two of them (the abductor pollicis longus and the extensor pollicis brevis) wind around the dorsal and lateral aspects of the radius. The remaining two muscles of the deep group are the supinator and the extensor indicis (Fig. 4-33).
The critical nerve in the area, the posterior interosseous nerve, innervates the muscles of the extensor compartment; it is the key anatomic structure from an operative point of view. The only major arterial supply of the compartment is the posterior interosseous artery.
Figure 4-31 Superficial muscles of the posterior aspect of the forearm.
Figure 4-32 The superficial muscles have been removed to reveal the course of the posterior interosseous nerve as it enters the supinator muscle through the arcade of Frohse and the course of the superficial radial nerve, which is sensory and supplies no muscles of the forearm.
Figure 4-33 The course of the posterior interosseous nerve through the supinator muscle, as it runs to supply muscles in the forearm.
Extensor Carpi Ulnaris. Origin. Common extensor origin on lateral epicondyle of humerus and subcutaneous border of ulna. (Shared origin with flexor carpi ulnaris.) Insertion. Base of fifth metacarpal. Action. Extensor and ulnar deviator of wrist. Nerve supply. Posterior interosseous nerve.
Extensor Digitorum Communis. Origin. Common extensor origin on lateral epicondyle of humerus. Insertion. Into extensor apparatus of fingers. Action. Extensor of wrist and fingers. Nerve supply. Posterior interosseous nerve.
Landmarks and Incision
Landmarks
The lateral epicondyle of the humerus, located just lateral to the olecranon process, is smaller than the medial epicondyle, but its lateral supracondylar line, which runs superiorly, is longer than the medial supracondylar line, extending almost to the deltoid tuberosity. The lateral epicondyle is the site of the common origin of the superficial muscles of the extensor compartment of the forearm. The extensor carpi radialis brevis, extensor digitorum communis, extensor digiti minimi, and extensor carpi ulnaris all originate from fused tendons that attach just anterior to the epicondyle. The brachioradialis and extensor carpi radialis longus arise from the lateral supracondylar ridge.
Tenderness over the common extensor origin occurs in lateral epicondylitis; the pain that is characteristic of this condition can be reproduced by providing resistance to extension of the wrist.
Compression of the posterior interosseous nerve at the arcade of Frohse may produce a syndrome similar to lateral epicondylitis. In these cases, the tenderness usually is elicited more distally in the course of the posterior interosseous nerve or anteriorly over the arcade of Frohse. Both conditions can exist in a single patient.28
Incision
A longitudinal incision on the posterior aspect of the forearm crosses the lines of cleavage of the skin at right angles and often leaves a broad scar.
Superficial Surgical Dissection
In the proximal half of the wound, dissection opens the plane between the extensor carpi radialis brevis and the extensor communis. In the distal third of the wound, the intermuscular plane lies between the extensor carpi radialis brevis and the extensor pollicis longus (see Fig. 4-31).
Deep Surgical Dissection
For the proximal third of the radius, dissection consists of detaching the insertion of the supinator muscle from the radius while preserving the posterior interosseous nerve (see Fig. 4-30).
For the middle third of the bone, dissection involves mobilizing and retracting two muscles, the abductor pollicis longus and the extensor pollicis brevis (see Fig. 4-29).
In the distal third of the radius, dissection opens the intermuscular plane between the extensor pollicis longus and the extensor carpi radialis brevis.
The proximal third of the radius is covered by the supinator muscle, through which the posterior interosseous nerve passes on its way to the posterior compartment of the forearm (see Figs. 4-32 and 4-33). For additional information on the supinator muscle, see the section regarding the anterior approach to the radius.
Dangers
Nerves
The posterior interosseous nerve is the motor nerve of the posterior compartment of the forearm. A branch of the radial nerve, it passes between the two heads of the supinator muscle and actually may come in direct contact with the neck of the radius or the extreme proximal end of the radial diaphysis. At that point, it may be trapped beneath incorrectly positioned plates. After emerging from the supinator muscle, the nerve passes distally over the origin of the abductor pollicis longus muscle to reach the interosseous membrane. It continues distally on the interosseous membrane to the level of the wrist joint, which it supplies with some sensory branches. The nerve supplies those muscles that arise from the common extensor origin and the deep muscles of the extensor compartment of the forearm (see Fig. 4-33).
When performing deep surgical dissection, it is important to remember that the posterior interosseous nerve is vulnerable during all approaches to the proximal third of the radial shaft. Although the nerve can be protected by detaching the insertion of the supinator and stripping the muscle off the bone subperiosteally, the only certain protection of the posterior interosseous nerve during plating of the upper third of the radius may come with full dissection via a posterior approach.
Vessels
The posterior interosseous artery accompanies the posterior interosseous nerve as it runs along the interosseous membrane in the proximal twothirds of the forearm. The posterior interosseous artery enters the extensor compartment of the forearm by passing between the radius and the ulna through the interosseous membrane (Fig. 4-34). The artery then joins the posterior interosseous nerve distal to the distal edge of the deep head of the supinator muscle.
The posterior interosseous artery is too small to be dissected easily down to the level of the wrist. Most of the blood supply for the posterior area comes from an anterior interosseous artery via branches that perforate the interosseous membrane. The tendons running in this area may have a marginal blood supply.
Although the artery may be damaged during the posterior approach to the radius, good collateral circulation appears to protect the extremity from any functional deficits (Fig. 4-35).
Figure 4-34 The origins and insertions of the muscles of the posterior aspect of the forearm.
Extensor Carpi Radialis Longus. Origin. Lower third of lateral supracondylar ridge of humerus, lateral intermuscular septum of arm. Insertion. Base of second metacarpal. Action. Extensor and radial deviator of wrist. Nerve supply. Radial nerve.
Extensor Carpi Radialis Brevis. Origin. Common extensor origin on lateral epicondyle of humerus and radial collateral ligament of elbow. Insertion. Base of third metacarpal. Action. Extensor and radial deviator of wrist. Nerve supply. Posterior interosseous nerve.
Supinator. Origin. From two heads. Superficial head: from lateral epicondyle of humerus, lateral collateral ligament of elbow, and supinator crest of ulna. Deep head: from supinator crest and fossa of ulna. Insertion. Anterior aspect of radius. Action. Supinator of forearm. Weak flexor of elbow. Nerve supply. Posterior interosseous nerve.
Extensor Pollicis Longus. Origin. Posterior surface of ulna in its middle third and from interosseous membrane. Insertion. Distal phalanx of thumb. Action. Extensor of thumb and wrist. Nerve supply. Posterior interosseous nerve.
Abductor Pollicis Longus. Origin. Posterior surface of ulna, posterior interosseous membrane, and middle third of posterior surface of radius. Insertion. Base of thumb metacarpal. Action. Abductor and extensor of thumb. Nerve supply. Posterior interosseous nerve.
Extensor Pollicis Brevis. Origin. Posterior surface of radius and interosseous membrane. Insertion. Base of proximal phalanx of thumb. Action. Extensor of proximal phalanx of thumb. Nerve supply. Posterior interosseous nerve.
Extensor Indicis. Origin. Posterior surface of ulnar shaft and interosseous membrane. Insertion. Extensor apparatus of index finger via ulnar side of tendon of extensor digitorum that runs to index finger. Action. Extensor of index finger. Nerve supply. Posterior interosseous nerve.
Extensor Digiti Minimi. Origin. Common extensor origin on lateral epicondyle of humerus. Insertion. Extensor apparatus of little finger. Action. Extensor of little finger. Nerve supply. Posterior interosseous nerve.
Figure 4-35 The bones of the posterior aspect of the forearm.
Anterior and Posterior Approaches for the Treatment of Forearm Compartment Syndrome
The forearm contains muscle compartments constrained by strong fascia.
Fractures and their associated soft tissue injury bleed and create edema which increases the pressure within these compartments. As the pressure increases, the venous return decreases; in certain cases, the pressure becomes so high that it reduces the arterial blood supply to the muscles and creates muscle ischemia. Muscle ischemia in turn creates more edema, further increasing compartment pressure. This is known as a compartment syndrome. It is important to note that compartment syndrome can occur without the presence of a fracture. Crushing injuries of the forearm especially those caused by rollers are a potent cause of this condition.
The resultant muscle ischemia produces pain disproportionate to the other injuries which is the cardinal presenting symptom. If the pressure within the compartment is not relieved within a short period of time, permanent muscle necrosis will occur with associated damage to the nerves traversing the affected compartment (Volkmann ischemic contracture). In extreme cases, arterial occlusion occurs, leading to gangrene. Note, however, that normal distal pulses occur in all but the very late stages of this condition and physicians should not wait until changes in pulse pressure occur before initiating treatment.
Treatment of compartment syndrome consists of dividing the fascia constraining the compartment thereby relieving the intercompartmental pressure. All affected compartments must be decompressed. In the forearm these are the anterior/flexor compartments (superficial and deep) and the posterior/extensor compartment.
Anterior Approaches for Flexor Compartment Decompression
The compartment most commonly affected in the forearm is the anterior forearm compartment. It can be decompressed by incising the deep fascia that covers it along its entire length. In cases of compartment syndrome, both the superficial and the deep compartments on the volar side should be released along with the posterior compartment. Two approaches are available for use—the central and the ulnar approach.29,30
Landmarks and Incisions
Landmarks
Central Incision. Palpate the lateral humeral epicondyle just lateral to the olecranon process on the distal humerus and the radial styloid process of the radius on the radial aspect on the distal end of the radius.
Ulnar Incision. Palpate the medial humeral epicondyle, the large subcutaneous bony mass that stands out on the medial side of the distal end of the humerus and the ulna styloid process on the distal end of the ulna.
Incisions
Central Incision. Make a longitudinal incision extending from just below the lateral epicondyle of the distal humerus to the radial styloid process (Fig. 4-36A).
Ulnar Incision. Make a longitudinal incision extending from just below the medial epicondyle of the humerus to a point about 1.5 cm lateral to the ulnar styloid (Fig. 4-37).
Figure 4-36 A: To decompress the flexor compartments of the forearm begin by making a longitudinal incision extending from the lateral side of the elbow crease to the radial styloid process. B: Deepen the skin incision to reveal the fascia covering the superficial flexor muscles and incise that fascia on the ulnar border of flexor carpi radialis. C: Incise the fascia overlying flexor digitorum superficialis to decompress the deep layer of the flexor musculature.
Internervous Plane. There is no internervous plane for use. In the central approach, division of the deep fascia is usually done between the palmaris longus muscle and flexor carpi radialis both of which are supplied by the median nerve.
In the ulnar approach the intermuscular plane used lies between the flexor carpi ulnaris and the medial side of the flexor digitorum superficialis both of which are supplied by the ulnar nerve.
Superficial Surgical Dissection
Central Approach. Divide the fascia in line with the skin incision. Identify the lacertus fibrosus just below the elbow and divide it carefully to decompress the median nerve. Identify the interval between the palmaris longus muscle and the flexor carpi radialis and gently develop this intermuscular plane (Fig. 4-36B).
Ulnar Approach. Incise the deep fascia in the line of the skin incision along the medial border of the flexor carpi ulnaris (Fig. 4-38).
Deep Surgical Dissection
Central Approach. Identify the muscle belly of flexor digitorum superficialis with its tendons emerging distally. Carefully divide the fascia overlying the anterior surface of the muscle (Fig. 4-36C).
Ulnar Approach. Develop a plane between the flexor carpi ulnaris and the flexor digitorum superficialis elevating the latter muscle. The median nerve should remain attached to the deep surface of the flexor digitorum superficialis. Move the ulnar nerve with the flexor digitorum superficialis. To do this ligate and divide any branches of the ulnar artery running into the flexor carpi ulnaris that tether the nerve to that muscle. Elevating the muscle will reveal the three deep muscles of the forearm—pronator quadratus, flexor pollicis longus, and flexor digitorum longus—all of which can be given an epimysiotomy (Fig. 4-39).
Figures 4-37 A: Ulnar approach for decompression of forearm compartment syndrome—make a longitudinal incision from the medial epicondyle of the humerus to the ulnat styloid. B: Incise the fascia overlying the flexor digitorum muscle to decompress the superficial flexor muscles.
Figure 4-38 Retract the flexor digitorum superficialis muscle radially to expose the ulnar nerve and vessels.
Figure 4-39 Expose the fascia covering the flexor digitorum profundus muscle and divide it longitudinally taking care to preserve the ulna nerve and vessels.
Figure 4-40 A: To decompress the posterior compartment, make a longitudinal incision overlying the posterior aspect of the forearm extending from the lateral humeral epicondyle to Lister tubercle. B: Incise the fascia overlying the posterior muscle mass in the line of the skin incision.
Dangers
The median nerve and the ulnar neurovascular bundle are potentially at risk during these extensive exposures. A knowledge of anatomy is critical since internervous planes cannot be exploited.
Posterior Approach to the Forearm for Compartment Syndrome Decompression
The posterior approach to the forearm for decompression of a compartment syndrome is only used for this one surgical indication.
Landmarks and Incision
Landmarks. Palpate the lateral humeral epicondyle just lateral to the olecranon process and Lister tubercle which lies about one-third of the way across the dorsum of the wrist from the styloid process of the radius.
Incision. Make a longitudinal incision starting just below the lateral epicondyle of the humerus and ending just proximal to Lister tubercle (Fig. 4-40A).
Internervous Plane
No internervous plane is used in this approach as surgical dissection only involves the division of the deep fascia.
Superficial Surgical Dissection
Incise the deep fascia in line with the skin incision. The fascial edges should spring apart. Preserve the extensor retinaculi at the level of the wrist joint (Fig. 4-40B).
Dangers
The posterior interosseous nerve runs in the substance of the supinator muscle. It should be safe if dissection is confined to simple division of the deep fascia.
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