Thumb Metacarpal Vascularized Bone Grafts for Scaphoid Nonunion
The thumb metacarpal vascularized bone graft was described in 1992, pedicled on the first dorsal metacarpal artery.1 Based upon our anatomical investigation, Yuceturk et al2 reported on their successful use of thumb vascularized bone grafts in the reconstruction of scaphoid nonunions in four patients. More recently, we reported on our clinical results in a larger series of patients.3,4
Indications
We perform this procedure for any scaphoid non-union that is older than 6 months.
Contraindications
Widespread radiocarpal and midcarpal arthritis
Previous trauma or surgery on the thumb metacarpal
Injury to the radial artery
Examination
On inspection, a bulge on the dorsoradial side of the wrist due to synovitis in the anatomical snuffbox may be perceived with a longstanding scaphoid nonunion.
Wrist range of motion and grasping and pinching strength are limited.
Palpation of the radial styloid and the scaphoid in the snuffbox is painful in nonunion of the middle and distal thirds of the scaphoid.
Forced radial deviation plus wrist flexion produces pain on the radial aspect of the wrist in middle and distal third nonunion.
In patients with proximal pole nonunion, pain is perceived on the dorsal side of the wrist. The Watson test5 may elicit pain and a crunching sensation, but axial pressure over the thumb is rarely painful.
Imaging
A standard anteroposterior (AP) radiograph should be obtained. Lateral and 45-degree oblique pronated Xray views of the wrist should be obtained bilaterally.
In the lateral view, the scapholunate angle is measured, and any difference of 10 degrees or more from the unaffected side is considered pathological. A radiolunate angle of > 15 degrees is consistent with a dorsal intercalated segmental instability (DISI).
The length of the scaphoid is measured in the posteroanterior (PA) view with ulnar deviation. Scaphoid shortening of even 1 mm may be seen with scaphoid collapse.
An AP view of the clenched wrist is obtained to exclude injury to the scapholunate ligament.
In the PA view, the site of nonunion is determined, together with the existence of any joint degeneration. Radial styloid pointing and decreased articular space are common but do not generally prevent reconstructive surgery.
A computed tomography (CT) scan can be used to differentiate between a nonvisible nonunion and fibrous consolidation of the scaphoid.
Magnetic resonance imaging (MRI) is indicated to study the vascular status of the proximal pole, but there is controversy over what the various findings actually indicate.6 Moreover, the gold standard by which to assess for vascularity in the proximal pole is bone bleeding during surgery.7 Bone bleeding assessment may miss either dead or viable zones in the proximal pole. We always treat proximal pole non-union with a vascularized bone graft; consequently, the MRI findings do not interfere with our surgical decision-making process.
Relevant Anatomy
The first dorsal metacarpal artery (FDMA), which is, on average, 1 mm in diameter, stems from the radial artery 5 to 10 mm proximal to the trapeziometacarpal joint (TMJ).
After its origin at the snuffbox, the FDMA traverses the TMJ from the ulnar to the radial side. At the base of the thumb metacarpal, it runs along the ulnar aspect of the insertion of the abductor pollicis longus (APL) tendon ( Fig. 26.1 ).
The artery then continues its course along the radial third of the dorsal side of the thumb metacarpal, in close contact with the periosteum, but within a layer of fascia.
The FDMA reaches the radial side of the metacarpal head and, at this level, forms an anastomosis with the radial palmar collateral artery of the thumb.
Initially, the FDMA runs between the extensores pollicis brevis (EPB) and longus (EBL). In the middle and distal thirds of the thumb metacarpal, the artery lies radial to the EPB. Two venae comitantes accompany the FDMA.
The FDMA gives off several osteoperiosteal branches along its course, the largest of which are situated in the proximal and distal thirds of the thumb metacarpal. The proposed bone graft is harvested from the metacarpal head, and the available pedicle has a length of > 50 mm.
Pearls
If the nonunion involves the proximal pole, the operation should be performed by a dorsal approach.
In waist and distal third nonunion, surgery is performed via a palmar approach.
The Linscheid maneuver8 corrects scaphoid alignment.
Do not exsanguinate the limb before tourniquet inflation, because the presence of blood inside the vessels helps to identify the first dorsal metacarpal artery. If there is difficulty visualizing the first dorsal metacarpal artery, milking the forearm from proximal to distal to fill the vessels with blood is an often effective maneuver.
Be gentle with the bone graft. During harvesting, maximal efforts should be made to chisel the graft shape exactly according to the measurements of the scaphoid defect. Further trimming or adjustments should be avoided, however, because this jeopardizes the vascular connections between the bone and pedicle.
In the postoperative period, the importance of early X-ray images is to detect graft extrusion or malposition. In the first weeks after grafting, assessment of bone healing, either by X-rays or CT scan, is not straightforward.
Eight weeks after surgery, if there is evidence of partial union on X-ray images, we discontinue the immobilization. In general, a partial union progresses to full union without additional casting.9
Surgical Technique
Palmar Approach
This approach is indicated for nonunion that involves the distal pole or waist of the scaphoid to correct the humpback deformity.
The surgical incision is made over the flexor carpi radialis and along the junction of the palmar and dorsal skin over the thenar eminence ( Fig. 26.2 ).
Once the nonunion is identified, all nonviable bone and fibrous tissue is removed ( Fig. 26.3 ).
The wrist is flexed to correct the dorsal deviation of the lunate, and the lunate is temporarily pinned to the radius.8 Then the wrist is extended and ulnar deviated, and the bone defect measured ( Fig. 26.4 ).
The vascularized bone graft then is harvested ( Fig. 26.5 ).
A 2 cm wide tunnel down to the tendinous insertion of the abductor pollicis longus is created.
The graft is then passed underneath the EPB and APL and pushed in a palmar direction toward the scaphoid defect ( Fig. 26.6 ).
The vascularized bone graft is placed transversally or longitudinally (depending on the size of the defect) in the bone defect and press-fitted into place ( Figs. 26.7 and 26.8 )
The vascular pedicle lies radially (when the bone graft is placed transversely) or distally (when the bone graft is placed longitudinally).
The scaphoid is fixed with two Kirschner wires (K-wires) ( Fig. 26.9 ).
The vascular pedicle is then inspected to detect any kinks, compression, or tension.
The capsular flaps are loosely approximated, and the subcutaneous layer and skin sutured.
Pitfalls/Complications
Graft extrusion is a potential complication, but this did not occur in our series.
Metacarpal fracture is another potential complication after bone harvesting. However, this complication was absent in our series, probably because we immobilize the thumb after scaphoid grafting.
The dorsolateral cutaneous nerve of the thumb is at risk during surgery, and the nerve should be protected. In our patients we have not observed permanent lesion of the nerve. A minor number of patients complained about postoperative paresthesias on the radial dorsal side of the thumb, which resolved spontaneously.
In one other patient, despite scaphoid healing, we failed to reconstruct the scaphoid length adequately. This patient underwent a second surgery, at which time a limited styloidectomy was performed to enhance pain control; a good outcome, in terms of pain relief, was achieved.
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