30 Thumb Metacarpal Vascularized Bone Grafts
Patients with scaphoid nonunion seek medical assistance for a variety of reasons, including pain, decreased range of motion, and diminished strength in the affected thumb and wrist. The appearance of symptoms tends to be gradual because patients largely compensate for their deficits by avoiding painful motions and altering their habits. Pain does not necessarily appear immediately with wrist motion; it can appear during the night after repeated use of the wrist or thumb during the day. Eventually, symptoms may become amplified by a second trauma, at which time scaphoid nonunion may be detected on plain radiographs. When symptomatic, scaphoid nonunion requires surgical repair.
Vascularized bone grafts have gained special attention in the treatment of scaphoid nonunion because of their enhanced effectiveness promoting healing relative to conventional bone grafts,1 , 2 even in difficult situations like avascular necrosis and in the presence of longstanding lesions.3 , 4
In 1992, we described harvesting bone grafts from the thumb, pedicled on the first dorsal metacarpal artery.5 Based upon our anatomical investigation, Yuceturk et al6 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.7 , 8 This chapter revises our list of indications, provides additional technical tips, and reports on the results we have obtained utilizing thumb metacarpal vascularized bone grafts in the treatment of scaphoid nonunion. Thumb metacarpal grafts can reach the scaphoid via either a dorsal or a palmar approach, depending upon the location of the nonunion, and this represents one major advantage of this graft.
▪ Physical Examination of Scaphoid Nonunion
On inspection, a bulge on the dorsoradial side of the wrist can be perceived when nonunion has been longstanding. In addition, patients exhibit limitations in wrist range of motion and in grasping and pinching strength. See Table 30.1 for the limitations that are present in longstanding nonunion of the middle and distal thirds, and of the proximal pole.
Palpation of the radial styloid and the scaphoid in the anatomical snuffbox is painful in nonunion of the middle and distal thirds of the scaphoid. Similarly, forced radial deviation plus wrist flexion produces pain on the radial aspect of the wrist in middle and distal third nonunion. Conversely, in patients with proximal pole nonunion, pain is perceived on the dorsal side of the wrist. In these patients, the Watson test may elicit pain and a crunching sensation, but axial pressure over the thumb is rarely painful.
▪ Preoperative Imaging
X-rays 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.
Alterations in the carpal angles and a DISI deformity are found in 60% of the nonunions that involve either the middle or the distal third of the scaphoid.7 These observations are important for adequate surgical planning. Alterations of the scapholunate angle and scaphoid length are not observed in proximal pole nonunion. Also, alterations in carpal height are not a common finding in scaphoid nonunion. Moritomo et al9 performed a three-dimensional computed tomographic (3–D CT) study of scaphoid nonunions and found that the location of the fracture line relative to the dorsal apex of the ridge of the scaphoid may be predictive of a DISI deformity. The dorsal ridge coincides with the site of attachment of the proximal part of the dorsal intercarpal ligament, just distal to the attachment of the dorsal component of the scapholunate interosseous ligament. These ligaments, along with the dorsal radiocarpal ligament, probably afford indirect dorsal stability of the scaphoid, which may explain why nonunions that are distal to the attachment of the dorsal intercarpal ligament and the dorsal component of the scapholunate interosseous ligament fall into DISI: the proximal pole extends and the distal pole flexes, resulting in a DISI deformity. When the nonunion is proximal to the dorsal ridge, the preserved ligamentous attachments of the distal fragment may prevent flexion of the distal fragment, which can explain the absence of a DISI deformity in the early stages. An anteroposterior (AP) view of the clenched wrist is obtained to exclude injury to the scapholunate ligament. Although this has been reported with acute fractures10 we have never observed this injury to occur concomitantly with scaphoid nonunion. In the PA view with the wrist clenched, we can observe the impact of a short scaphoid on the styloid process ( Fig. 30.1 ).
On 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. Conversely, more advanced degenerative changes that affect the midcarpal joint can halt scaphoid reconstruction and result in a need for salvage surgery. In fact, in 17 patients in whom we observed radiographic indications of wrist arthritis, during surgery, we noted that the cartilage of the radiocarpal joint largely was preserved in 15.7
We rarely use CT and MRI when evaluating the scaphoid nonunion. Sometimes, a CT scan can be used to differentiate between a nonvisible nonunion and fibrous consolidation of the scaphoid. MRI is indicated to study the vascular status of the proximal pole, but there is controversy over what the various findings actually indicate.11 Moreover, the gold standard by which to assess for vascularity in the proximal pole is bone bleeding during surgery.12 Bone bleeding assessment may miss either dead or viable zones in the proximal pole. We always treat proximal pole nonunion with a vascularized bone graft; consequently, the MRI findings do not interfere with our surgical decision-making process.