69 Nonunion of the Proximal Pole
69.1 Introduction
Most common scaphoid nonunions occur in the middle third caused by fractures through the waist. Proximal pole fractures, which are often missed due to less clinical symptoms, lead to the pattern of proximal pole nonunion. These patterns represent significant differences. Nonunions through the waist have an increased risk for unstable situations leading to humpback deformity with a collapsed and shortened scaphoid; however, blood supply and bony architecture are preserved. In contrast, nonunions at the proximal pole usually do not lead to humpback deformity, but have a higher risk of avascularity due to the pattern of blood supply demonstrating incoming vessels in the distal and middle of the scaphoid. In progressive cases, even complete loss of bony architecture is seen.
69.2 Patient History Leading to the Specific Problem
A young machine fitter when 19 years old got open dorsal screw fixation due to a proximal pole fracture of the scaphoid of his left wrist. After 6 weeks of immobilization, the patient returned to work without further clinical examination and X-ray control. Two years later, he was referred to our institution with complaints at his wrist under load.
69.3 Anatomic Description of the Patient’s Current Status
Clinical examination showed reduced motion by 40–0-60 degrees of extension/flexion and grip strength by 80% compared to the uninjured hand. Plain radiographs revealed nonunion of the scaphoid at the proximal pole and loosening around the cannulated mini-screw (▶Fig. 69.1a). An MRI of the wrist performed elsewhere was not really helpful due to the interference caused by the screw. Additionally, a CT scan was performed and the resorption areas around the screw were confirmed as well as additional complete loss of bone stock and architecture of the proximal pole (▶Fig. 69.1b). Based on this information, we did not believe bony union could be achieved by conventional techniques or by local vascularized bone graft.
69.4 Recommended Solution to the Problem
We decided to replace the proximal pole completely by free vascularized osteochondral graft transplantation from the femoral condyle (▶Fig. 69.2).
With respect to the morphology, in his original 1984 classification, Herbert differentiated five types of nonunion, which were later modified and reduced to four types, where the occurrence on plane radiographs and CT is typical for each type. D1 represents a fibrous nonunion where the shape of the scaphoid bone is maintained by fibrous connecting tissue. D2 means complete nonunion with mobile fragments and significant resorption area. In D3, sclerosis is seen at the nonunion side with increased defect and in D4 necrotic bone with loss of bony architecture is observed (see▶Fig. 69.1b).
The situation has to be clearly defined when comparing different treatment strategies for nonunion of the proximal pole. Assessment of blood supply by MRI and bone morphology by CT scan, and duration of the nonunion represent major prognostic factors.
Since vascularized bone grafts have gained popularity, assessment of avascularity of the proximal fragment based on preoperative MRI findings is frequently performed. It must be remembered that a precise assessment of vascularity with MRI can only be obtained if an intravenous contrast agent, gadopentetate, is used. With this technique, assessment of vascularity preoperatively may be useful. But there is a concern that avascular necrosis (AVN) is often diagnosed by the presence of a simple signal loss on plain T1-weighted images. The term AVN should be only used when there is loss of bone stock or even fragmentation due to long-standing avascularity. Signal loss in contrast MRI and loss of punctuate bleeding intraoperatively should be used to indicate an avascular or ischemic fragment. Recent studies, however, have given more importance to the morphological structure of the proximal pole defined by a CT scan. As long as the structure according to D1 to D3 (▶Fig. 69.3) is preserved, bony healing even with nonvascularized graft can be expected. In the case of destroyed bony architecture according to D4 (AVN), bony union with traditional techniques is no more possible. In these situations, transplantation of free vascularized osteochondral grafts from the femoral condyle with complete replacement of the proximal pole has proven to be a real reconstructive solution, avoiding salvage procedures such as resection and replacement by a pyrocarbon implant or partial wrist fusion.
