Effect of Fracture Reduction with Different Medial Cortical Support on Stability After Cephalomedullary Nail Fixation of Unstable Pertrochanteric Fractures: A Biomechanical Analysis

Background This study evaluated the biomechanics of the proximal femoral nail antirotation-II (PFNA-II) in AO/OTA 31A2.2 intertrochanteric fractures based on the fracture reduction quality. Methods Unstable intertrochanteric fractures were created according to the AO classification and repaired by proximal femoral nail antirotation-II (PFNA-II) using one of three medial cortical support groups. The specimens were tested using cyclic axial loading. The following parameters were recorded: force and stiffness at failure, maximum vertical and horizontal displacement, neck-shaft angle, and location and patten of failure. Results In the cyclic loading test, the force at failure in the anatomical reduction (AR) group was greater than that of the positive medial cortical support (PMCS) group (984.22 ± 12.63 vs. 936.95 ± 16.78) N ( P < 0.05) and negative medial cortical support (NMCS) group (918.04 ± 28.86) N ( P < 0.05). The stiffness in the AR group was 4.77 and 31.9% higher than that in the PMCS group ( P > 0.05) and NMCS group ( P < 0.05). The maximum vertical displacement was the largest in the NMCS group. The maximum horizontal displacement in the NMCS group was 28.6 and 19.1% larger than that in the AR group ( P > 0.05) and PMCS group ( P < 0.05). The neck-shaft angle in the NMCS group was smaller than that in the anatomic reduction group ( P < 0.05) and positive support group ( P < 0.05). Conclusion For the unstable AO/OTA 31A2.2 intertrochanteric fracture, there were significant differences in their mechanical stability among AR, PMCS and NMCS. The NMCS is not recommended during the intraoperative reduction.