Cartilage Defect Articulation With the Proximal Phalanx After Retrograde Intramedullary Screw Fixation of Metacarpal Fractures: A Cadaveric Study.

Purpose: Retrograde intramedullary screw fixation for metacarpal fractures has become increasingly popular; however, the technique requires violation of the extensor mechanism at the metacarpophalangeal (MCP) joint and penetration of the metacarpal articular surface. Although prior studies have quantified the proportion of metacarpal articular surface involved in screw placement, none have evaluated how the resulting cartilage defect articulates with the proximal phalanx at the MCP joint as a potential source of altered wear patterns. Methods: In a cadaveric study, six specimens (24 metacarpals) underwent fixation of simulated metacarpal neck fractures with either a 3.6 or a 4.5 mm metacarpal-specific screw inserted via peritendinous or percutaneous approach. The location and percentage of the metacarpal head articular surface damage were measured. The MCP joint was then taken through a full arc of motion in all planes to map contact between the metacarpal defect and the proximal phalanx articular cartilage. Results: Retrograde screw placement resulted in an average of 8% metacarpal articular surface damage. The percutaneous approach produced a significantly more volar starting point compared with the peritendinous approach. Across the simulated arc of motion, 100% of the proximal phalanx articular cartilage came into contact with the cartilage defect on the metacarpal head. Conclusions: Retrograde metacarpal screw fixation produces a focal cartilage defect on the metacarpal head that tracks across the entire proximal phalanx articular surface during MCP joint motion. Clinical relevance: This focal damage articulating with the entire base of the phalanx may alter contact stress, potentially accelerating degradation and predisposing to MCP arthritis over time.