The biomechanical effects of femoral neck shortening on femoral head and neck

Abstract

Objective Using finite element analysis to study how the biomechanics of femoral head and neck changes after neck shortening, and discuss the mechanism of obvious higher osteonecrosis of the femoral head (ONFH) rate in femoral neck shortening cases. Methods MIMICS was used to build three femoral neck fracture models with Pauwells angle of 70 degrees. The neck lengths of the three models respectively were normal, 2.5 mm shortened and 5.0 mm shortened. Every model was assembled with 3 hollow screws, and imported into the finite element analysis software ABAQUS. The stress change of femoral head and neck was analyzed by loading and restraint. Results When the femoral neck length was normal, 2.5 mm shortened and 5.0 mm shortened, the maximal tensile stress of hollow screws in upper part of the femoral neck was 15.7, 14.1 and 12.4 mPa, and the compressive stress of lower part of femoral neck was 20.2, 19.1 and 17.8 mPa, respectively. Meanwhile, the high stress bearing district was transfered to right above the femoral head from its superior lateral quadrant, and the maximum stress of non-main stress bearing district was 10.6, 12.8 and 17.2 mPa respectively. Conclusion The femoral neck shortening reduces the proximal femoral eccentricity. It doesn’t affect the stabilities of internal fixation and fracture ends, but it transfers the stress bearing district of femoral head and causes the forming of high stress bearing district in non-main stress bearing district. Key words: Femoral neck fracture; Femoral neck shortening; Biomechanics