Biomechanical comparison of intramedullary and percutaneous pin fixation for proximal humeral fracture fixation

The purpose of this study was to investigate the mechanical strength and durability of intramedullary nailing (IM) and percutaneous pinning (PP) for fixation of three-part proximal humeral fractures using a cadaveric model.

Three-part surgical neck fractures were created in paired embalmed cadaveric humeri. Fractures were fixed with IM and PP fixation. The fixation stiffness and durability was assessed under cyclic rotational loading (infraspinatus) ramping from 0.1 to 1.25 Newton-meters for 10,000 cycles. The specimen were then torsionally loaded to failure.

Mechanical testing was performed using a servohydraulic test system (MTS, Minneapolis, MN, U.S.A.).

PP fixations were accomplished using standard multiplane techniques. IM fixation was attained using an 11.0-millimeter-diameter curved rod interlocked proximally with three splayed 5.0-millimeter cancellous screws and distally with three 3.5-millimeter cortical screws.

During cyclic loading the reconstruction stiffness, angular migration, and angular displacement per cycle were measured and compared between fixation methods. The ultimate torque at failure, absolute angular migration, and reconstruction stiffness during failure were recorded and compared between fixation methods during destructive testing.

The intramedullary device had greater stiffness and less angular displacement of fragments during cyclic loading. When loading the reconstructions to failure, the intramedullary device proved to have greater failure torques, stiffness, energy absorbed, and angular displacement before failure.

This biomechanical study showed that the IM device provided a stronger, more stable, and durable fixation option than did PP fixation for large-fragment multipart proximal humeral fractures with minimal comminution.