8.3.1 Indications

Metacarpophalangeal joint (MCPJ) arthritis is commonly rheumatic or inflammatory but can also occur after trauma or with age-related degeneration. The index and middle finger MCPJs are typically affected first. ^{5 , 6} Silicone arthroplasty is considered in patients with severe pain, deformity, or loss of function. Arthroplasty is favored in rheumatoid patients when ulnar drift and volar subluxation cannot be passively reduced.

8.3.2 Contraindications

Silicone MCPJ arthroplasty is contraindicated in patients with poor wound healing capacity, inadequate soft tissue, infection, excessive bony erosion, or fatty replacement of the bone with inability to support an implant.

8.3.3 Preoperative Evaluation

In rheumatoid patients, wrist deformity and distal radioulnar joint (DRUJ) instability must be addressed before the MCPJs. Radial deviation of the wrist leads to progressive ulnar drift at the MCPJs, and DRUJ instability can result in attritional rupture of the extensor tendons. Examination of the MCPJs often reveals ulnar subluxation of the extensor tendon into the valley between the metacarpal heads (Fig. 8.1). If the MCPJ deformity is passively correctable, soft tissue reconstruction is possible—synovectomy and extensor tendon centralization with cross-intrinsic transfer of the ulnar lateral band. Arthroplasty is indicated when the deformity is severe (>15 degrees of ulnar drift or >20 degrees of extensor lag) or cannot be passively corrected.

In scleroderma patients, boutonniere deformities are common. Sclerosis of the joint capsule, collateral ligaments, and flexor tendon sheath and attenuation of the central slip lead to volar displacement of the lateral bands and flexion contracture at the proximal interphalangeal joint (PIPJ). Patients compensate by hyperextending the MCPJ (Fig. 8.2).

Standard, three-view radiographs of the affected joint are required. Bone quality is assessed for its ability to accept an implant. Articular damage, loss of joint space, joint incongruity, and bony alignment are evaluated (Fig. 8.3). Radiographs of the wrist are also obtained if any pathology is suspected.

8.3.4 Surgical Anatomy

The MCPJ is an asymmetric condylar joint—the ovoid articular surface of the metacarpal fits into an elliptical cavity at the base of the proximal phalanx. The metacarpal head is sloped volarly and ulnarly. Motion is permitted in two planes: flexion-extension and radioulnar deviation.

The volar plate, collateral ligaments, and extensor mechanism stabilize the joint. The sagittal bands center the extensor tendon over the joint and prevent bowstringing during hyperextension. The intrinsic muscles insert onto the lateral bands which pass volar to the axis of rotation of the MCPJ and produce flexion, adduction, and adduction forces (Fig. 8.4).

The MCPJ is commonly affected in rheumatoid arthritis. Attenuation of the radial collateral ligament from synovitis results in volar subluxation of the proximal phalanx and ulnar drift of the fingers. Chronic joint subluxation contributes to intrinsic muscle contracture which may require release and cross-intrinsic transfer at the time of arthroplasty. Alternatively, in lieu of ulnar lateral band releases, the metacarpal head can be aggressively resected to decrease the tension on the lateral bands.

8.3.5 Approach

The dorsal approach provides expeditious access to the MCPJ. A longitudinal or lazy-S incision centered at the joint is used for access to a single MCPJ. Multiple arthroplasties are performed through a single, extended transverse incision (Fig. 8.5) or multiple longitudinal incisions. Care is taken to preserve the dorsal veins to reduce postoperative swelling.

8.3.6 Authors’ Preferred Technique

The skin is incised and the subcutaneous tissue is elevated off the extensor mechanism. The radial sagittal band is incised and the extensor tendon is retracted. The joint capsule is incised longitudinally and synovectomy is performed. The collateral ligaments are released at their proximal attachment on the metacarpal head. A sagittal saw is used to remove the articular surface of the metacarpal head (Fig. 8.6). The MCPJ should then easily reduce into normal alignment. If the joint remains tight or the finger ulnarly deviated, ulnar intrinsic release is performed. If soft tissue tightness persists, consider release of the volar plate or resection of additional metacarpal bone.

An awl is used to open the medullary canals of the proximal phalanx and metacarpal. The medullary canals of the proximal phalanx are prepared first for index, middle, and small finger MCPJ arthroplasty. For the ring finger, the order is reversed due to the narrow canal of the fourth metacarpal; the metacarpal is broached first and the implant size determined before preparing the proximal phalanx to avoid over reaming.

On the proximal phalanx, the starting point of the awl is at the junction of the dorsal and middle third of the articular surface. The awl is inserted with a gentle twisting motion. The smallest distal broach is then inserted straight into the medullary canal of the proximal phalanx in the path created by the awl (Fig. 8.7). Orientation of the broach must be maintained during insertion and withdrawal—typically, the numbered side of the broach is placed parallel with the dorsal cortex. If the broach is twisted, it may asymmetrically enlarge the medullary cavity and create a poor fit with the implant stem. The broach should be inserted to its full depth to create enough space for the implant stem. Take care to insert the broaches along the central axis of the phalanx—breaking the dorsal or volar cortex can destabilize the implant. Broaches are increased in size until the desired implant size is reached.

The same process is repeated for the metacarpal. With the articular surface removed, the awl inserts easily into the medullary canal. Broaches are sequentially inserted to their full depth until the implant size is reached. The largest implant that the medullary canal will accept is selected for a snug fit.

Before implant insertion, the metacarpal is prepared for radial collateral ligament repair. Repair is mandatory to restore joint alignment and improve stability during pinch. Two 0.035-inch (0.89 mm) Kirschner wires are drilled through the dorsal radial metacarpal cortex at the distal end of the cut bone. A braided 3–0 permanent suture is passed through these holes and left untied (Fig. 8.8). This suture is used later to reattach the radial collateral ligament to the metacarpal.

A temporary implant sizer is selected based on the largest broach size used. The sizer is oriented so that the cavity of the barrel faces volarly. The proximal stem is inserted first into the metacarpal, then the distal stem into the proximal phalanx. The stems should fit easily into the broached medullary canals and the implant should not compress or buckle during motion. If this occurs, the implant may be too large or the broached canal too short. More bone may need to be resected from the metacarpal. If the fit is adequate, the sizer is removed and the final implant is opened. After verifying the correct orientation, the implant is inserted in the same sequence using two clean, smooth forceps and a no-touch technique (Fig. 8.9). Flexion and extension are tested intraoperatively.

The joint is held in extension while the soft tissues are repaired. The radial collateral ligament is imbricated using the suture previously placed through the metacarpal. When the radial collateral ligament is severely attenuated and repair is not possible, a distallybased flap of the volar plate is elevated and anchored to the metacarpal. The joint capsule is repaired using a braided 3–0 permanent suture. Tight repair of the radial collateral ligament and joint capsule with the finger extended limits the flexion arc by 10 to 20 degrees but stabilizes the joint.

Lastly, the extensor tendon is centralized to prevent recurrence of ulnar drift. In longstanding deformity, the ulnar sagittal band becomes fibrotic and requires release. The radial aspect of the extensor hood is imbricated to the radial sagittal band (Fig. 8.10). The MCPJ is passively flexed and extended to ensure the extensor tendon remains centralized through the arc of motion.

The skin is closed using 4–0 nylon sutures and the patient is splinted with the MCPJs extended.

8.3.7 Postoperative Care

Patients are seen in the office 2 weeks after surgery for suture removal. Dynamic, short-arm extension splinting with the wrist extended at 20 degrees and the MCPJs fully extended and radially deviated continues for 6 weeks. After 6 weeks, patients are allowed to increase activity (Fig. 8.11).