Comparative biomechanical evaluation of a pin-sleeve transfixation system in cadaveric calf metacarpal bones.

Objective To compare proximal fragment displacement and the peri-implant strain using a pin-sleeve cast (PSC) system and a transfixation pin cast (TPC) system on a cadaveric calf metacarpal bone fracture model. Study Design Experimental. Sample Population Cadaveric calf metacarpal bones (n = 6 pairs). Methods Paired samples were instrumented with either the TPC or the PSC systems. Strain gauges were applied proximal to the transfixation implants and the bones encased in cast material. The distal part of the construct was removed to mimic an unstable distal comminuted fracture. Constructs were fixed to the material testing machine and initially loaded in axial compression in their elastic range to determine construct stiffness. Constructs were loaded cyclically with a sinusoidal curve that increased until failure. Variables compared statistically between constructs were the initial construct stiffness and, at given load points, the mean metacarpal axial displacement in loading and unloading condition and mean axial strain. Results Initial construct mean +/- SD axial stiffness was not significantly different between constructs (PSC: 689 +/- 258; TPC: 879 +/- 306 N/mm). There was no significant difference between either investigated displacements of metacarpal bones transfixed with PSC and those transfixed with TPC at all load points. The PSC constructs had a significant decrease in the recorded mean strain (502 +/- 340 mu strain) compared to the TPC construct (1738 +/- 2218 mu strain). Conclusions The PSC significantly reduced peri-implant strain with comparable axial displacement to the TPC in cadaveric calf metacarpal bones.