RESUMO
OBJECTIVE: Biomechanical comparison between locked plating and retrograde nailing of supracondylar femur fractures with simulated postoperative weight-bearing. METHODS: The Locking Condylar Plate (LCP) and Retrograde/Antegrade EX Femoral Nail (RAFN) were tested using 10 paired elderly cadaveric femurs, divided into Normal and Low Bone Mineral Density (BMD) groups, with a simulated AO/OTA type 33-A3 supracondylar femur fracture. Each specimen was subjected to 200,000 loading cycles in an attempt to simulate six weeks of postoperative recovery with full weight-bearing for an average individual. The construct's subsidence due to cyclic loading, and axial stiffness before and after the cyclic loading were measured and their correlation with BMD was studied. The two implants were compared in a paired study within each BMD group. RESULTS: LCP constructs showed higher axial stiffness compared to RAFN for both Normal and Low BMD groups (80% and 57%, respectively). After cyclic loading, axial stiffness of both constructs decreased by 20% and RAFN constructs resulted in twice as much subsidence (1.9 ± 0.6mm). Two RAFN constructs with Low BMD failed after a few cycles whereas the matched pairs fixed with LCP failed after 70,000 cycles. CONCLUSIONS: The RAFN constructs experienced greater subsidence and reduced axial stiffness compared to the LCP constructs. In Low BMD specimens, the RAFN constructs had a higher risk of failure.
