Biomechanical Effects of Stretching Exercise on Site of Femoral Subtrochanteric Fracture

The biomechanical effects of an intramedullary nail system for treating subtrochanteric fracture during bone healing is still unclear. The aim of this study was to analyze the stress conditions of a subtrochanteric fracture model implanted with an intramedullary nail system and augmentation plate under stretching exercise. Two displacement conditions assuming stretching exercise were considered. The finite element (FE) model of a subject undergoing surgery with the intramedullary nail system and augmentation plate was constructed based on post-operative computed tomography images. A 1-mm-thick callus was set in the gaps positioned at the fracture line. Bone healing was defined as a change in the Young's modulus of the callus. The orced displacements from the medial and lateral sides were applied to the distal part of the FE model, respectively. In the initial stage of bone healing, there was a noticeable difference between stress distributions of the callus under displacements from the medial and lateral sides. The compressive stress was widely distributed in the callus by the displacement from the lateral side. However, the tensional stress in the callus was increased by displacement from the medial side. Stretching exercise, such as displacement from medial direction, carries a risk of non-union.