BIOMECHANICAL COMPARISON OF INTRAMEDULLARY AND PERCUTANEOUS PIN FIXATION FOR PROXIMAL HUMERAL FRACTURE FIXATION

Objectives: The purpose of this study was to investigate the mechanica l strength and durability of intramedullary nailing (IM) and percutane ous pinning (PP) for fixation of three-part proximal humeral fractures using a cadaveric model. Design: Three-pari surgical neck fractures w ere created in paired embalmed cadaveric humeri. Fractures were fixed with IM and PP fixation. The fixation stiffness and durability was ass essed under cyclic rotational loading (infraspinatus) ramping from 0.1 to 1.25 Newton-meters for 10,000 cycles. The specimen were then torsi onally loaded to failure. Setting: Mechanical testing was performed us ing a servohydraulic test system (MTS, Minneapolis, MN, U.S.A.). Inter vention: PP fixations were accomplished using standard multiplane tech niques. IM fixation was attained using an 11.0-millimeter-diameter cur ved rod interlocked proximally with three splayed 5.0-millimeter cance llous screws and distally with three 3.5-millimeter cortical screws. M ain Outcome Measurements: During cyclic loading the reconstruction sti ffness, angular migration, and angular displacement per cycle were mea sured and compared between fixation methods. The ultimate torque at fa ilure, absolute angular migration, and reconstruction stiffness during failure were recorded and compared between fixation methods during de structive testing. Results: The intramedullary device had greater stif fness and less angular displacement of fragments during cyclic loading . When loading the reconstructions to failure, the intramedullary devi ce proved to have greater failure torques, stiffness, energy absorbed, and angular displacement before failure. Conclusions: This biomechani cal study showed that the IM device provided a stronger, more stable, and durable fixation option than did PP fixation for large-fragment mu ltipart proximal humeral fractures with minimal comminution.