Effect of Femoral Head Size on Contact Pressure and Wear in Total Hip Arthroplasty
Total hip arthroplasty using artificial materials is a widely used treatment for osteoarthritis and similar disabling conditions. The hip is essentially a ball and socket joint, linking the “ball” at the head of the thigh bone (femur) with the cup-shaped “socket” in the pelvic bone. The longevity of total hip arthroplasties is significantly reduced by the wear of joint surfaces. Prosthetic implant wear and joint degeneration mechanism can be estimated for the hip joint by predicting contact area and pressure distribution during activities of daily living which provide biomechanical rationales for preoperative planning and postoperative rehabilitation. The objective of the current study was to generate a finite element model capable of predicting the influence of femoral head size and coefficient of friction between femoral head and cup on contact pressure distribution as well as wear in total hip replacement. These stress distributions represent an important factor which affects the development of hip and also determines the state of health or disease of the adult hip. Moreover, the understanding of wear behavior will aid in the evaluation of the clinical penetration measurements of patients with hip arthroplasty and design of THR devices. Furthermore, the prediction of contact pressure and wear rates can help in deciding for a treatment and in planning the operation. The finite element models were generated using ANSYS finite element software by developing an ANSYS Parametric Design Language macro for easy and quick calculations. A standardized femur was used as a basis for the FEM models. This study has demonstrated that the increasing of head diameter can reduce the maximum contact pressure between the metallic femoral head and the Ultra High Molecular Weight Poly-Ethylene cup. Furthermore, wear penetration was found to decrease asymptotically with increasing head size and the predicted wear rates were well within clinically observed ranges for each component size.