Evaluation of hip impingement kinematics on range of motion

Femoroacetabulare impingement (FAI) is a mechanical mismatch between femur and acetabulum. It would bring abnormal contact stress and potential joint damage. This problem is more common on people with high level of motion activity such as baler dancer and athletics. FAI causes pain in hip joints and consequently would lead to reduction in range of motion. This study investigates whether changing the kinematics parameters of hip joint with impingement can improve range of motion or not. Hip joint model is created in finite element environment, and then the range of motion was detected. The original boundary conditions are applied in the initial hip impingement model. Then gradually the gap between femur and acetabulum in the model was changed to evaluate the changing kinematics factors on range of motion. Mimics (Materialise NV) software was used to generate the surface mesh of three-dimensional (3D) models of the hip joint from computerised tomography (CT) images of the subject patients diagnosed with FAI. The surface mesh models created in Mimics were then exported to Abaqus (Simulia Dassault Systems) to create a finite element (FE) models that will be suitable for mechanical analysis. The surface mesh was converted into a volumetric mesh using Abaqus meshing modules. Material properties of the bones and soft tissues were defined in the FE model. The kinematic values of the joint during a normal sitting stance, which were obtained from motion capture analysis in the gait lab, were used as boundary conditions in the FE model to simulate the motion of the hip joint during a normal sitting stance and find possible contact at the location of the FAI. The centre of rotation for a female hip model with impingement was changed and range of motion was measured in Abaqus. The results were compared to investigate the effect of centre of rotation on range of motion for hip with femoroacetabular impingement. There was a significant change on range of motion with changing the gap between femur and acetabulum. Decreasing the distance between femur and acetabulum decreases the range of motion. When the distance between femur and acetabulum changes the location of impingement shifted. Increasing the distance between femur and acetabulum, there is no noticeable change in the location of impingement. This study concludes that changing the kinematics of hip with impingement changes the range of motion.