Metacarpal shaft fractures: the effect of shortening on the extensor tendon mechanism.

Spiral and oblique metacarpal shaft fractures frequently develop shortening through the fracture site. The acceptable amount of fracture shortening has not been well established. The goal of this study was to elucidate the acceptable limits of metacarpal shaft fracture shortening in a cadaver model by assessing the magnitude of the metacarpophalangeal (MCP) joint extensor lag produced. Nine fresh-frozen cadaver hands were used to create a metacarpal shaft fracture model in the second and fifth metacarpal bones. Sequential shortening up to 10 mm in 2-mm increments was performed. The results revealed an average of 7 degrees of extensor lag at the MCP joint produced for every 2 mm of metacarpal shortening. The capacity of the MCP joint for active hyperextension may compensate for the extensor lag produced by metacarpal shortening in the clinical setting.