A biomechanical analysis of locking plate fixation with minimally invasive plate osteosynthesis in a subtrochanteric fracture model

Objective:The objective of this study was to establish the relative fixation strengths of a locking plate, a dynamic condylar screw (DCS) plate, and a long proximal femoral nail (PFN). Methods:The study involved three groups of composite large femoral synthetic bones of five specimens per group; plating using a locking compression plate-distal femur (LCP-DF), plating using a DCS plate, and nailing using a long PFN. A gap osteotomy model was used to simulate a comminuted subtrochanteric femur fracture. For each femur, a minimal preload of 100 N was applied before loading to failure. A vertical load was applied at 10 mm/min until femur failure. Load to failure, mode of failure, and displacement at load to failure were documented. Results:Fixation strength (load or moment to failure) of LCP-DF (1,330 N; range, 1,217-1,460 N) was 26.6% and was greater in axial loading compared with DCS (1050.5 N; range, 956.4-1194.5 N) and 250% less in axial loading compared with long PFN (3633.1 N; range, 3337.2-4020.4 N; p = 0.002). Ultimate displacement in axial loading was similar for LCP-DF (18.4 mm; standard deviation [SD], 1.44), DCS (18.3 mm; SD, 3.25), and long PFN (16.7 mm; SD, 1.82). Conclusions:The LCP-DF construct proved stronger than the DCS in terms of ultimate strength by biomechanical testing of a simulated subtrochanteric femur fracture with comminution. Although the nail construct proved strongest, the biomechanical performance of the locking plate construct may lend credence to the use of a locking plate versus the DCS plate for minimally invasive plate osteosynthesis of subtrochanteric femur fractures, which may be technically difficult to fix using a nail.