48 Intraoperative Instability During Metacarpophalangeal Joint Arthroplasty for Osteoarthritis
48.1 Patient History Leading to the Specific Problem
A 63-year-old, right-hand-dominant man presents to a tertiary hand center complaining of poor grip strength, decreased arc of motion, and persistent pain at his right long and ring finger metacarpophalangeal (MCP) joints. The patient sustained a crush injury 3 months prior to presentation for which he underwent amputation of the right index finger, just distal to the MCP joint. His original surgical team did not attempt any operative interventions at his other joints. Given his ongoing pain and minimal deformity, we offered him staged pyrocarbon implant arthroplasty, beginning with the long finger MCP joint. Intraoperatively, his MCP joint was contracted and dislocated, with the proximal phalanx base positioned volar to the head of the metacarpal. After resecting the head of the metacarpal, the joint became unstable.
48.2 Anatomic Description of the Patient’s Current Status
Anticipating intraoperative instability begins with identifying the appropriate inclusion and exclusion criteria for pyrocarbon arthroplasty. Owing to their nonconstrained design, pyrocarbon implants rely on good press fit into medullary bone and robust ligamentous support for stability. Before performing pyrocarbon arthroplasty, the surgeon must ensure that the patient has adequate cortical bone stock to support the implant. The surgeon must also confirm that the extensor mechanism, collateral ligaments, and capsular components of the joint are intact, or at least amenable to operative repair. Preoperative evaluation should always include three-view radiographs to delineate the degree of joint congruity and assess the cortical bone stock.
On physical examination, this patient demonstrated loss of active and passive range of motion at both the long and ring finger MCP joints, likely secondary to dense adhesions of the extensor apparatus (▶Fig. 48.1). When stressed in the radial and ulnar directions, neither joint proved unstable, suggesting the collateral ligaments were intact. Preoperative radiographs demonstrated loss of MCP joint congruity, destruction of the joint surface, and subluxation of the proximal phalanx base below the long metacarpal head (▶Fig. 48.2). Given his irreducible joint incongruity and proximal phalanx dislocation, we planned to perform radical bone resection and joint mobilization at the time of arthroplasty. Finally, owing to poor extensor tendon excursion, we planned extensor tenolysis to improve joint mobility.
48.3 Recommended Solution to the Problem
Intraoperative instability can occur even with meticulous technique, so it is important to understand the salvage maneuvers to remedy an unfavorable situation. Upsizing the distal and/or proximal implant can be an effective initial measure, as larger implants bridge tissue gaps to achieve better contact between implant components. In instances of ligamentous laxity or collateral ligament damage, repairing the ligament primarily or reconstructing the ligament with a tendon graft can restore soft-tissue stability.
In cases of intraoperative fracture, poor bone or soft-tissue support, or multifactorial instability, immobilization with external fixation provides the most structural integrity. External fixation not only keeps joints aligned, but immobilization allows repaired soft tissues to heal. Finally, if these techniques fail, surgeons may exchange pyrocarbon for constrained silicone prostheses. Here, external fixation was most appropriate.
48.3.1 Recommended Solution to the Problem
• In joints with large tissue gaps, upsizing implants can bridge space to improve implant apposition and stability.
• Collateral ligaments may be repaired primarily or with tendon reconstruction to further improve soft-tissue support.
• If the joint is unstable intraoperatively, an external fixator with pins placed proximal and distal to the implant immobilizes the joint for 6 to 8 weeks.
• If all other salvage maneuvers fail, the pyrocarbon implant may be exchanged for a constrained silicone implant.
48.4 Technique
48.4.1 Intraoperative Instability
As with preoperative examination, mitigating intraoperative instability starts with precise operative technique: fastidious attention to implant placement is key. We gain access to the joint through the sagittal band, which spares the extensor mechanism and preserves overall joint stability (▶Fig. 48.3). To select an appropriate place to ream the metacarpal, we identify the collateral ligament insertion on the dorsolateral depression of the metacarpal head and choose an entry point a safe distance away. On the cross-sectional axis, we advance the starter awl at a point one-third the distance to the dorsal cortex and ulnar to midline. We use fluoroscopy to confirm we have not seated implant stems in a radial position, as this will place the joint at risk for ulnar drift and subsequent instability. We ream the proximal phalanx in a similar fashion.
