Comparative biomechanical study of reversed less invasive stabilization system and proximal femoral nail antirotation for unstable intertrochanteric fractures

Objective Unstable intertrochanteric fractures(ITFs) are mostly treated by proximal femoral nail antirotation(PFNA), Inter-Tan, Asian Hip, and other new internal fixation devices. But for complex unstable fractures, such as crushed lateral wall of the greater trochanter, the loss of fixation point on lateral wall slightly reduces the fixing effect. This study aimed to compare the biomechanical strengths between reversed less invasive stabilization system(LISS) and PFNA for treatment of unstable ITFs.Methods Forty synthetic femurs were used to simulate unstable ITFs in vitro and were fixed using the reversed LISS or PFNA. These fractures were divided into two groups depending on whether the lateral wall of the greater trochanter is intact or not(AO classification: 31-A2.3 and 31-A3.3, respectively). The load-displacement of femur, stiffness, ultimate load, and cyclic fatigue resistance were detected using an incremental load test and a dynamic fatigue test through an MTS 858 test system.Results For both 31-A2.3 and 31-A3.3, the vertical sinking displacement(VSD) of the femoral head under 500 N load was insignificantly smaller after treatment with reversed LISS than with PFNA, and when the displacement was 5 mm, the femoral head bore insignificantly greater load. The fixation with reversed LISS resulted in greater axial stiffness of the femur but smaller ultimate load. During the same cycle in the dynamic fatigue test, the VSD was insignificantly smaller with the fixation of reversed LISS.Conclusion Reversed LISS and PFNA have similar biomechanical strength for unstable ITFs. This conclusion should be supported by additional large-size research on basic biomechanics and clinical application. This is the first comparative biomechanical study comparing reversed LISS and PFNA for unstable ITFs.