Volar Wedge Bone Grafting and Internal Fixation of Scaphoid Nonunions
Volar Wedge Bone Grafting and Internal Fixation of Scaphoid Nonunions
DEFINITION
The scaphoid is the most commonly fractured carpal bone in the wrist. Scaphoid fractures that fail to heal after 6 months of treatment are categorized as nonunions and represent about 5% to 10% of all scaphoid fractures.
Untreated nonunions reportedly lead to progressive arthrosis and wrist pain.6
Volar wedge bone grafting is an effective surgical technique in the treatment of certain scaphoid nonunions based on the following:
Location of the fracture Degree of the deformity Vascularity of the scaphoid
This general technique can also be adapted to increase its versatility.
ANATOMY
Nearly 80% of the scaphoid's surface is covered by articular cartilage.6
Through ligamentous connections, the scaphoid serves as the bridge or link between the proximal and distal rows (FIG 1). Due to these strong tethers proximally and distally, it is highly susceptible to an acute fracture after a fall on an outstretched hand.18
Other key factors that influence scaphoid fracture healing are its tenuous vascular supply and its unique bony architecture.
The vulnerable vascularity of the scaphoid, especially the proximal pole, is well described in the literature.8,14,15,16,20 This is the result of the scaphoid's retrograde blood supply, with approximately 70% of the vascular supply provided through the dorsal ridge vessel and 30% through branches to the scaphoid
tubercle (at the level of the radiocarpal joint via superficial palmar branch perforators off the radial artery).
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FIG 1 • Anatomy of the wrist joint. The scaphoid bridges the proximal and distal carpal rows and is largely covered by articular cartilage.
The complex geometry of the bone makes it difficult to anatomically reduce the bone fragments.
PATHOGENESIS
Although there may be a variety of reasons for the development of a scaphoid nonunion, a fractured scaphoid usually fails to heal for three primary reasons:
The fracture is either undetected or untreated within the first 4 weeks after the injury.
The location of the fracture is proximal, resulting in poor vascularity of the most proximal fragment. The fracture is displaced more than 1 mm.
NATURAL HISTORY
Scaphoid nonunion advanced collapse (SNAC), described in the literature, is a predictable sequence of changes that occurs as a result of scaphoid nonunion leading to wrist arthrosis, often associated with pain and limitation of motion.4,5
In studying patients with painful wrists over a 15-year period to determine who will develop symptoms, it is evident that the incidence of symptomatic wrist pathology requiring reconstruction is significantly higher for
scaphoid nonunions that have gone untreated.1
Techniques used to detect an acute scaphoid fracture and its susceptibility to nonunion, wrist pain, and corresponding arthrosis have been discussed in great detail in the literature.14,15,20
PATIENT HISTORY AND PHYSICAL FINDINGS
The patient who presents with a scaphoid nonunion is usually a man between the ages of 18 and 35 years.
Unrecognized injuries in adolescence may present with pain related to early SNAC wrist arthrosis in the middle-aged adult.
Patients generally complain of wrist pain that limits range of motion or hinders activities such as push-ups, weightlifting, or simple daily tasks such as opening a door. Moderate to heavy pinch and grip pain have also been described.
A specific event resulting in the original scaphoid fracture years before is rarely cited by the patient on presentation.
Consistent physical examination findings include subtle tenderness in the region of the scaphoid tubercle or the anatomic snuffbox, limited wrist extension compared to the contralateral side, and localized pain on the radial side along the radiostyloid or scaphoid with loaded wrist extension. If arthrosis has developed, soft tissue swelling may be noted over the dorsal and radial wrist.
IMAGING AND OTHER DIAGNOSTIC STUDIES
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Standard radiographs include posteroanterior (PA), lateral, and scaphoid oblique 45- and 60-degree pronated views (FIG 2). Such views
Confirm the diagnosis
Provide information regarding displacement, angulation, shortening, and the presence of a “humpback deformity”
Reveal compensatory carpal instability, dorsal intercalated segment instability (DISI)
As part of a treatment algorithm, dividing scaphoid fracture nonunions into either proximal, middle, or distal is very helpful.
Other factors considered in diagnostic assessment include previous wrist fracture or sprain later becoming symptomatic; tenderness on the scaphoid tubercle or in the anatomic snuffbox; localized pain to the radial side of the wrist along the radiostyloid or scaphoid itself, with a loaded dorsiflexed wrist; and pinching and heavy grip pain.
Once the scaphoid nonunion is diagnosed, a computed tomography (CT) scan performed in the plane of the scaphoid helps define bony architecture. Sagittal and coronal images are particularly helpful in characterizing the nonunion site and its orientation, displacement, and degree of bone loss.
Scaphoid collapse (or humpback deformity) is most clearly determined by measuring the lateral intrascaphoid angle on the sagittal CT views.
Magnetic resonance imaging (MRI), especially when combined with intravenous gadolinium, is helpful in defining the presence or absence of osteonecrosis and any associated ligamentous or cartilaginous injuries. If
osteonecrosis of the proximal fragment is seen, the surgeon should consider a vascularized bone graft10 (see Chap. 38) rather than the nonvascularized grafting procedure described in this chapter.
DIFFERENTIAL DIAGNOSIS
De Quervain tendinitis Scaphotrapeziotrapezoidal arthritis
Scaphoid lunate instability, static, and dynamic
FIG 2 • An oblique view of a scaphoid that has not healed. Radial styloid fracture
Trapezial ridge fracture
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NONOPERATIVE MANAGEMENT
Surgery is generally indicated for established scaphoid nonunions that are displaced and symptomatic because of the strong likelihood that radiocarpal arthrosis may develop with this type of persistent nonunion.18,20
Nonoperative management may be appropriate for minimally symptomatic scaphoid nonunions. All factors should be taken into consideration when determining the most appropriate treatment: Scaphoid nonunion alone is not an absolute reason for surgery.12
SURGICAL MANAGEMENT
Volar wedge bone grafting is the preferred surgical technique for treatment of a scaphoid nonunion without osteonecrosis but with shortening, an increased intrascaphoid angle causing a humpback deformity, and concomitant carpal collapse. Although many scaphoid nonunions without deformity can be effectively treated with the described procedure, other approaches and grafting techniques that are less invasive may be an
option, especially for proximal pole nonunions.2
Determining which bone graft is necessary depends on how much shortening is anticipated.3
The benefits of distal radius bone grafting include its location within the same surgical field and can be
harvested as a vascularized or nonvascularized graft. One important disadvantage is the creation of a relatively large defect and stress riser within the distal radius. Also, it is not possible to obtain a bicortical or a tricortical piece of bone for a more structural bone graft.
Iliac crest bone graft may be harvested in large quantities and as a bicortical or tricortical piece of bone. It is relatively simple to procure and has a long history of success in such cases, a standard by which all others are currently measured. The disadvantages of this type of bone graft include a separate incision with associated morbidity as well as a reported risk of cutaneous nerve injuries. Also, it cannot be converted to a vascularized pedicle bone graft.
When an MRI reveals the presence of osteonecrosis, a vascularized procedure should be considered (see Chap. 38).14,15,20
Preoperative Planning
After assessing all diagnostic studies, including plain films, MRI and CT scans, the type of bone graft is determined.
Two types of fixation screws can be used.
One type of screw has a smooth shank and two threaded heads. This screw is strong and creates high compression but may not be appropriate for all nonunions. The scaphoid nonunion fragments must be large enough to ensure that no threads of the screw cross into the bone graft site and yet the screw can be completely buried within the bone.
The other type of compression screw uses a deferential pitch between the proximal and distal portion of the screw. This screw may be more versatile, although it lacks compression strength compared to the above mentioned screw.
If compression screws are not deemed appropriate for the type of nonunion that exists, multiple K-wires can be used.
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A regional anesthetic block is used for most patients and is helpful for alleviating postoperative pain. When iliac crest grafting is chosen, additional general anesthesia is needed.
All radiographic studies are reviewed and brought to the operating room for reevaluation during the case.
Positioning
The patient is placed in the supine position with the upper extremity positioned on a hand table.
If an ipsilateral iliac crest bone graft is used, the hip on the same side as the affected hand is prepared and draped. A small bump is placed under the hip for patients with significant adipose tissue.
A tourniquet is applied to the proximal arm.
Approach
The location of the scaphoid nonunion helps determine the surgical approach. Wedge bone grafting of a waist nonunion is performed using a standard volar approach.
For proximal pole fractures with evidence of osteonecrosis, a dorsal or dorsal radial approach with use of a vascularized bone graft should be considered.13,19
TECHNIQUES
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Volar Wedge Bone Grafting Using Distal Radius Bone Graft and Intraosseous Compression Screw Fixation
Incision and Initial Dissection
An incision is drawn over the flexor carpi radialis (FCR) tendon and extended distally between the glabrous skin of the thenar eminence toward the distal pole of the scaphoid. The incision should be angled across the wrist flexion crease (TECH FIG 1A).
After exsanguination, the skin is incised, and the FCR tendon is identified. Distally in the wound, a volar branch of the radial artery is often sacrificed to gain exposure (TECH FIG 1B).
The floor of the FCR tendon is sharply incised over the entire course of the incision, and the digital flexors and median nerve are swept ulnarly. They are carefully protected throughout the case. A blunt Wheatlander is used to maintain visualization of this interval between the radial artery and the FCR tendon.
The volar extrinsic ligaments, the radioscaphocapitate (RSC) and long radiolunate (LRL), are identified and precisely incised in line with the incision. Much of the LRL and a portion of the RSC are left intact, helping to stabilize the proximal pole (TECH FIG 1C).
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TECH FIG 1 • A. The skin incision is marked out. B. The volar branch of the radial artery is often sacrificed to gain exposure. C. After the floor of the FCR is longitudinally divided, a portion of the RSC ligament is visualized.
This stability facilitates the reduction of the distal fragment to the proximal fragment.
Preserving this ligamentous support also helps maintain fracture reduction during the placement of an intraosseous compression screw by counteracting the torque created during screw insertion.
Deep dissection proceeds to the scaphotrapezial joint. This interval is exposed using a transverse capsular incision allowing for later insertion of the intraosseous screw.
The articulation between the scaphoid and capitate is carefully exposed. This visualization is important to confirm reduction of the scaphoid fragments.
During exposure, it is critical to avoid dissection over the distal dorsoradial scaphoid to avoid interrupting the contribution by the dorsal ridge vessel.
Nonunion Exposure and Preparation
A no. 64 Beaver blade and Freer elevator are used to define the location of the nonunion and the borders of the scaphoid itself. Time spent here makes eventual reduction and bone graft placement simpler (TECH FIG 2A,B).
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TECH FIG 2 • A,B. A Freer elevator identifies the nonunion site. C. K-wires are used as joysticks to control the scaphoid proximal and distal fragments. D. Manipulation of the K-wires allows for access to the nonunion site for débridement and then graft placement.
Two joystick K-wires are placed, one angled proximally in the proximal fragment and one angled distally in the distal fragment (TECH FIG 2C).
These K-wires facilitate manipulation of the fragments and therefore access to the nonunion site for
débridement (TECH FIG 2D).
The proximal and distal poles are examined carefully for osteolysis and sclerosis. A small curette or rongeur is used for débridement and removal of intervening fibrous tissue. Débridement is complete once good punctate bleeding is noted. In some situations, deflating the tourniquet temporarily can be of value in assessing viability of the fragments.
Fracture Reduction and Preliminary Stabilization
By bringing the joysticks/crossed K-wires into a more parallel position (relative to one another) and rotating the distal K-wire into slight supination, the humpback deformity is improved, and the initial fracture reduction is accomplished (TECH FIG 3).
A retrograde K-wire may be inserted along the longitudinal axis of the scaphoid to temporarily hold the reduction.
If placed in an appropriately eccentric position, this K-wire may serve effectively as a derotation K-wire during screw insertion and yet remain out of the path of the screw.
Restoration of scaphoid length and anatomic reduction of the fragments are best assessed by direct visualization and fluoroscopy.
Lateral images will reveal correction of the DISI deformity.
PA images document proper length of the scaphoid and determine if the Gilula lines are reestablished.9
The size of the volar wedge graft needed to maintain the reduction is now determined based on the volar defect noted after the reduction is accomplished.
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TECH FIG 3 • The scaphoid joysticks are used to reduce the fracture, and the length is estimated to determine the size of the volar wedge graft.
Distal Radius Graft Harvest
A two-fingerbreadth incision is made more proximally than initially described. This provides the necessary access to the volar distal radius.
The pronator quadratus is elevated using cautery, and the distal radius is perforated using K-wires to outline the size of the graft needed to fill the volar defect in the scaphoid.
Great care is taken to avoid destabilizing the radial cortex of the radius. The orientation of the longer limb of the rectangular graph is distal proximal.
A curved osteotome introduced on three sides allows harvest of the corticocancellous wedge. A curette is then used to harvest as much cancellous bone as necessary.
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TECH FIG 4 • A. The wedge placement is complete. B,C. PA and lateral views of the compression bone screw after harvesting the bone graft from the distal radius.
Graft Contouring and Insertion
The volar cortical defect in the reduced scaphoid is “regularized” using a small water-cooled sagittal saw or a fine rongeur.
Very little bone is removed from the fracture fragments to create a standard-shaped trough. Creating such a “regular” defect makes insertion of the wedge graft easier and more secure.
The same saw or rongeur is used to shape the corticocancellous graft to match the regularized defect.
The prepared proximal and distal fragments are packed with cancellous bone, and the corticocancellous graft is tapped into place (TECH FIG 4A).
Before graft insertion, the longitudinal K-wire, whether it is the K-wire placed to maintain reduction or the K-wire over which the cannulated compression screw is to be placed, is withdrawn into the distal pole and then reinserted after placement of the graft into the trough.
Cannulated Intraosseous Compression Screw Fixation
At the level of the scaphotrapezial joint, a small rongeur is used to remove a portion of the trapezial lip.20
This facilitates placement of the K-wire and screw down the center longitudinal access of the scaphoid. A center screw position on all fluoroscopic views has been demonstrated to lead to increased healing rates.
A K-wire from the compression screw system is then inserted in a retrograde direction (distal to proximal)
into the center of the scaphoid, perpendicular to the fracture line.
If the K-wire is not perpendicular to the fracture, compression generated from the screw may malreduce the fragments.
Once the K-wire is in perfect position, as judged fluoroscopically, and is fixed in the far (proximal) cortex of the scaphoid, the length is measured.
Factors such as cartilage thickness and distance between the fracture fragments is taken into account. It is critical that the screw not be too long and not enter the radiocarpal joint.
Although some surgeons advocate advancing the K-wire into the distal radius after the measurement is taken so that the wire
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remains in position during drilling, that practice is dangerous. It is preferable to leave the K-wire in the scaphoid.
Advancing the K-wire can result in cutting the guidewire during drilling or screw placement (particularly with a second-generation compression screw that has cutting flutes at the distal end).
If not already present, an eccentric K-wire is placed to maintain the reduction during screw insertion.
Under fluoroscopic guidance, a cannulated drill is used followed, in some cases, by a cannulated bone tap.
Especially during drilling, the surgeon must be careful to remain parallel with the wire.
The corticocancellous bone graft must be visualized at all times during these procedures to make certain position is maintained. Maintaining finger pressure over the graft during screw insertion is helpful.
Imaging confirms proper screw location, fracture reduction, and construct stability. The K-wire is removed from the cannulated screw, and the eccentric K-wire is removed (TECH FIG 4B,C).
The wound is then irrigated, and the volar extrinsic ligaments are repaired precisely with permanent suture. The remainder of the joint capsule may be closed with an absorbable suture.
Bone filler, preferably cadaver dried cancellous bone chips, can be inserted into the distal radius harvest site with a small tamp to compress and fill the defect. This potentially decreases the risk of hematoma formation. The periosteal sleeve is then closed over the distal radius with absorbable suture.
Skin is closed using nylon suture, and the tourniquet is then deflated after placement of a thumb spica splint.
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K-Wire Fixation
If compression screw fixation is not feasible, then retrograde, nonthreaded K-wires are recommended and placed in the same manner as described earlier for the bone screw.
The wires should be left under the skin and removed once the bone has healed.
K-wires provide adequate stability and may be a better fixation choice with large bone grafts as well as small proximal or distal fragments.
Iliac Crest Graft Harvest
Rather than obtaining bone graft from the distal radius, a standard technique of harvesting bone from the iliac crest may be used.16,20
A 2- to 3-cm incision is made just inferior to the superior border of the iliac crest just posterior to the anterior superior iliac spine (ASIS).
The incision is kept below the belt line to minimize postoperative incisional tenderness.
The incision is posterior to the ASIS to avoid iatrogenic nerve injury and subsequent numbness and pain
over the proximal lateral thigh.
Dissection is accomplished using cautery through the deep fascia down to the crest. The superior crest is exposed and muscles are released from a portion of the outer table using cautery and an elevator.
A water-cooled sagittal saw and a curved osteotome are used to harvest a bicortical segment of corticocancellous graft.
The graft is slightly larger than the measured defect in the scaphoid. The inner table is left intact.
The harvested outer table will be volar when the graft is placed in the scaphoid and the superior crest will be radial.
A curette is used to harvest cancellous bone graft.
The wound is copiously irrigated and temporarily packed with thrombin-soaked Gelfoam while attention is redirected to the scaphoid.
After the scaphoid is reconstructed, the Gelfoam is removed and the wound is again irrigated. If indicated, a small suction drain is placed below the fascia.
The wound is closed in layers with a running locking stitch used for the fascia.
A local anesthetic with epinephrine may be injected before harvest of the graft or after closure.
PEARLS AND PITFALLS
When MRI reveals osteonecrosis in a scaphoid nonunion
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Volar wedge bone grafting and internal fixation is the treatment option that is most effective when applied to scaphoid waist fractures, distal-third fractures of the scaphoid without osteonecrosis, or scaphoid waist fractures with concomitant carpal collapse and a nondissociated DISI pattern. When osteonecrosis is present, a vascularized procedure may be preferable.
Surgeon prefers an adaptable graft should physical findings during the procedure reveal osteonecrosis not revealed on MRI
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The advantage of harvesting from the distal radius rather than the iliac crest exists when the MRI is inconsistent with physical examination findings during the procedure. Harvesting from the distal radius allows the surgeon to use a modified pedicle technique using the pronator quadratus and the periosteum of the distal radius and place it into the volar defect as a
vascularized bone graft if necessary.20
Fixation for greatest chance of bone healing
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Although either compression bone screws or K-wires can be used as effective fixation in this procedure, compression screws are believed to improve chances of overall bone healing.7,11,18
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POSTOPERATIVE CARE
When a screw is placed for internal fixation, a thumb spica splint is applied after the procedure.
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The patient returns for a follow-up visit 10 days after surgery. During this visit, the hand is examined for swelling and sutures may be removed.
A thumb spica, short-arm cast is applied, leaving the interphalangeal joint free. The patient is followed radiographically at intervals of 3 to 4 weeks.
CT scans are the most predictable way to determine if the scaphoid has healed. This evaluation is recommended before allowing the patient to resume vigorous activities.
OUTCOMES
Symptomatic scaphoid nonunions with shortening respond well to volar wedge bone grafting with internal fixation, particularly when scaphoid length is restored and when any bony union is achieved.
A higher rate of bone healing is achieved when a compression bone screw is used as the internal fixation. Reported results show that internal fixation leads to better functional results than standard techniques of bone grafting.7,11,16,17,18
Bones failing to heal after the procedure have been shown to respond well to vascularized grafts. Other options for failure to heal include partial scaphoid excision, complete scaphoid excision with four-corner fusion, proximal row carpectomy, radial styloidectomy, and complete wrist fusion.
COMPLICATIONS
Radiographic findings may not match the findings at surgery. This affects the outcome to varying degrees, depending on the type of graft harvested.
Persistent nonunion and osteonecrosis resulting in wrist arthrosis
Scarring associated with repair of the capsule, causing some postoperative stiffness
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