Intramedullary Screw Fixation of Distal Metacarpal Fractures: A Biomechanical Study.

PURPOSE: Intramedullary headless compression screw (IHCS) fixation of metacarpal (MC) fractures is popular. A concern for distal fractures is the potential loss of fragment/head fixation and with intra-articular incursion of hardware. We evaluated the biomechanical stability of IHCS fixation of progressively distal MC osteotomies using a cadaveric simulated active motion model.

METHODS

We included 12 matched-pair fresh-frozen cadaveric hands (median age, 73.5 years; 75% men), excluding matched-pair fingers with deformities/severe arthritis at the metacarpophalangeal joint or proximal interphalangeal joint. Bone cuts were made in each MC creating a gap simulating comminuted unstable fractures. The distal edge of each gap was 15, 10, and 5 mm proximal to the dorsal edge of the MC head cartilage. Matched pairs of fingers were used for each of these osteotomy levels, with the 15 mm versus 5 mm pairs as our primary comparison group. Each MC osteotomy was stabilized with a retrograde IHCS, excluding matched pairs with any inadequate MC isthmus fit. Each hand was loaded into a simulated active finger motion model, with finger flexion and extension driven by a computer-controlled linear actuator. Each finger underwent 2,000 cycles of full extension to flexion movement to simulate 6 weeks of immediate postoperative full active range of motion. Displacement at the osteotomy sites was measured with a differential variable reluctance transducer with defined failure as >1 mm of displacement.

RESULTS

There were significant differences in group-level failure rates and average maximum distal fragment displacement between the 15 and 5 mm osteotomy level matched pairs and the 10 and 5 mm matched pairs.

CONCLUSIONS

Intramedullary headless compression screw fixation of distal MC gapped osteotomies was significantly less stable at 5 mm proximal to the MC head dorsal articular margin.

CLINICAL RELEVANCE: Providers should consider these findings when advising patients on immediate full active range of motion following IHCS fixation of comminuted, unstable distal MC fractures.