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INTRODUCTION
Nonunion of the scaphoid represents a common and disabling problem of the wrist. The goal of treatment is to achieve union to prevent secondary arthritic changes, that is, a scaphoid nonunion advanced collapse (SNAC) pattern leading to a painful wrist. The current preferred approach involves a resection of the pseudarthrosis, bone grafting, and rigid stabilization using a headless bone screw. Some of the key factors that influence the chances for union include the delay from trauma to surgery as well as the grading of the scaphoid blood supply.
PATTERNS OF NONUNION
Most scaphoid nonunions are due to fractures through the waist. Proximal pole fractures may also lead to nonunion, since they may have minimal symptoms and are hence missed. Nonunions involving the middle third of the scaphoid are inherently unstable and may lead to a humpback deformity with a collapsed and shortened scaphoid ( Fig. 22-1 ).
In contrast, nonunions of the proximal pole usually do not lead to a humpback deformity, but have a higher risk of avascular necrosis because the scaphoid blood supply enters through the dorsal ridge vessels at the distal pole and waist ( Fig. 22-2 ). Follow-up studies report a union rate for nonvascularized bone grafts of about 90% for nonunion at the waist and about 70% for the proximal pole. To improve these results, vascularized bone grafts were initially popularized by Zaidemberg and colleagues with later refinements by Shin and Bishop.
ASSESSMENT OF BLOOD SUPPLY
Vascularized bone grafts are indicated when there is compromised blood supply to the proximal part of the scaphoid. Intraoperative bleeding points after release of the tourniquet are the most reliable way to assess the vascularity of the bone. Preoperative magnetic resonance imaging (MRI), however, has a high correlation with the intraoperative findings provided contrast is used.
A normal T1-weighted image is indicative of viable bone. When there is a loss of the bone marrow signal there is a diminished T1 signal ( Fig. 22-3 A). The use of gadolinium is mandatory to distinguish between avascular bone and marrow edema. T2 fat-saturated imaging may show enhancement, which is indicative of marrow edema ( Fig. 22-3 B), or no enhancement, which is synonymous with avascular bone ( Fig. 22-4 A and B). In our prospective series including 60 patients, the concurrence between MRI and intraoperative bleeding points showed confirmation with a rate of 92%.
There is still much confusion over the interpretation of MRI findings. It is important to know the difference between scaphoid vascularity and histologic findings in avascular bone. MRI can give information about blood supply but not about histology. This means that the diagnosis of true avascular necrosis cannot be done made on an MRI based on the simple loss of bone marrow signal during T1 imaging. MRI might be used to distinguish among perfusion, absent perfusion, and disturbed blood supply with edema. Avascular necrosis is defined histologically as a loss of the bony architecture with an absence of osteocytes and empty lacunae. Most of the nonperfused bones in scaphoid nonunion, however, still show a preserved bony architecture, which is a prerequisite for a successful revascularization procedure ( Figs. 22-1 and 22-2 ). Avascular necrosis with a destroyed bony architecture similar to that seen in Kienböck´s disease is only rarely seen in scaphoid nonunion. In this situation, there is no real reconstructive solution ( Fig. 22-5 ).
INDICATIONS FOR VASCULARIZED BONE GRAFTS
An advantage of vascularized bone grafts is a better blood supply that theoretically can lead to faster healing. Indications include failed surgery, in which a free bone graft and stabilization by headless bone screw did not lead to union, and nonunion with a nonperfused proximal fragment as demonstrated by MRI or intraoperative inspection.
CONTRAINDICATIONS TO VASCULARIZED BONE GRAFTS
Disadvantages of vascularized grafts include a wider dissection, which leads to more scarring, difficulties related to correcting a humpback deformity, and difficulties related to stable fixation, which might interfere with the vascular pedicle. Nonvascularized bone grafts can be rigidly fixed with a headless bone screw or, in the case of revision, with a small grid plate. For these reasons, I believe that vascularized grafts should be recommended only if vascularity is reduced.
TYPES OF VASCULARIZED GRAFTS
Pedicled vascularized grafts have been harvested on branches of the radial artery, on the palmar, and the dorsal aspect of the radius. The choice between a palmar and a dorsal approach is dictated by the location of the pseudarthrosis as well as the need to correct a scaphoid humpback deformity. 10
Palmar Grafts
Anatomy
The anatomic basis for a vascularized bone graft pedicled on the palmar carpal arch was initially described by Kuhlmann and associates. Haerle and associates dissected 40 fresh cadaver arms injected with colored latex. They found that the palmar carpal arch arises in the distal forearm at a median of 1.2 cm (range 1–2.5 cm) proximal to the tip of the radial styloid. This artery along with its vena comitans cross the palmar aspect of the distal forearm just distal to the pronator quadratus and consistently formed a T-shaped anatomosis with the anterior branch of the anterior interosseous artery. They found that grafts harvested from the distal ulnar aspect of the radius could be pedicled on the radial branch of the palmar carpal arch and could easily reach the scaphoid.
Surgical Technique
In cases of a volar collapse and shortening of the scaphoid as occurs with the humpback deformity, the harvest of a pedicled bone graft from the palmar aspect of the distal radius is preferred. The standard palmar approach to the scaphoid is used with extension of the skin incision proximally along the flexor carpi radialis ( Fig. 22-6 A). The wrist is flexed to release tension off the flexor tendons. The radial artery is dissected out without necessarily identifying the origin of the palmar carpal artery, which runs horizontally just distal to the pronator quadratus. The bone graft is ideally harvested from the palmar ulnar aspect of the radius to get enough length of the pedicle to reach the scaphoid nonunion ( Fig. 22-6 B). Approximately 1 cm of bone is harvested by using an osteotome on each side of the pedicle. Care is taken to avoid penetrating the distal radioulnar joint by using a temporary Kirschner (K) wire as a marker. The periosteum is incised distally and proximally to the expected location of the pedicle, and the pedicle is dissected periosteally along its radial half. After harvest of the graft, the pedicle is mobilized back to the radial artery, and the graft is packed anteriorly in the prepared nonunion area. If necessary, additional cancellous bone from the iliac crest may be used. If there is still enough bone stock, fixation can be performed with a headless bone screw or alternatively with two K wires while taking care not to injure the pedicle. The pin is kept in place for at least 6 weeks, and the patient is immobilized in a short-arm cast until union is achieved.
