The operation is performed through a dorsal or longitudinal incision created over the MP joint (Fig. 1). If the extensor tendons are intact and not displaced ulnarly, the extensor mechanism is opened longitudinally over thejoint. If the extensor tendon is subluxed, the sagittal bands are incised on the radial side ofthe central tendon to facilitate centralization at the completion of the case. The extensor hood is separated from the capsule, and the capsule is then incised in a longitudinal fashion.
Excess synovium is removed in addition to any large dorsal osteophytes.
With the joint exposed, the starter awl is used to identify the medullary canal of the metacarpal (Fig. 2). The alignment and cutting guide is then placed within the medullary canal (Fig. 3). An oscillating saw is placed within the saw guide and used to start the cut dorsally to the center of the guide (Fig. 4). The angle of the cut is 27.5°. Once the osteotomy has been initiated, the guide is removed and the remaining portion of the osteotomy is completed freehand (Fig. 5).
The proximal phalanx is then prepared using the same sequence as was used for the metacarpal osteotomy (Fig. 6). The cutting guide for the proximal phalanx provides a 5° back cut (Fig. 7). During both proximal and distal osteotomies every attempt is made to preserve the collateral ligaments and as much bone length as possible.
The medullary canals of both the metacarpal and proximal phalanx are now prepared with the broaches (Fig. 8). The medullary bone is impacted; however, in cases of significantly sclerotic bone (as is the case in many patients with OA), the canal may need to be enlarged with a side-cutting burr. The canals of the metacarpal and proximal phalanx are prepared until they are able to accept the largest implant that will fit in the proximal phalanx. Intraoperative fluoroscopy is used
liberally throughout the case to ensure central placement of all broaches and awls within the coronal and sagittal planes. Implants should not be mismatches; this differs from proximal interpha-langeal joint surface replacement arthroplasties, in which mismatching between the proximal and distal component is possible. Broaching is stopped when the sized reamers are seated just below the bone edge. Final implants tend to be slightly larger than trial components (Fig. 9). Trial implants are then placed and the joint is reduced. The MP joint should move passively through a 0° to 90° arc without significant tension (Fig. 10). In patients who have longstanding osteoarthritis or post-traumatic arthritis, when flexor contractures are present, release of the volar plate or intrinsic release and reinsertion may also be necessary to gain full extension. Ulnar release is often required in rheumatoid patients for joint rebalancing.
Trial implants are removed and permanent implants are placed. Dorsal and palmar stability are tested, and collateral ligaments are reinserted if they required resection or release during implant placement. Fluoroscopy is used to verify implant position before closure. The dorsal capsule is trimmed to allow for a snug repair over the prosthesis. The extensor mechanism is closed with radial imbrication of the hood to centralize the tendon over the MCP joint (Fig. 11). In cases of RA, the ulnar hood can be cut free of the central tendon if it is too tight to allow for imbrication. The remainder of the wound is closed in the standard fashion. The hand dressing is applied to maintain the digits in extension at the MP joint and allow for some functional flexion at the interphalangeal joints. Radiographs are taken in the postoperative
dressing to ensure there has been no subluxation during dressing application.
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