ADAPTIVE BONE REMODELLING FOLLOWING TOTAL KNEE ARTHROPLASTY: A FINITE ELEMENT STUDY

Abstract

Introduction: Periprosthetic bone resorption following total knee arthroplasty (TKA) is becoming a clinical concern. Decrease in bone quality jeapordises implant fixation, consequently leading to revision surgery. It has been suggested that a reduction in the local stress distribution may cause a decrease in bone mineral density (BMD). Computational bone remodelling has been used previously to predict bone adaptation in total hips. However, little has been reported on its use in TKA remodelling simulations. The aim of this study was to simulate the bone remodelling response of the femur and tibia following TKA, using an adaptive bone remodelling algorithm combined with the finite element (FE) method.

Methods: 3D femur and tibia models were constructed from human cadaveric computed tomography images. Total knee implant geometries were used to reconstruct the knee joint.(RBK, Global Orthopaedic Technology, Australia). Both the femur and the tibia models were loaded at 45% gait cycle for normal walking gait using loads based on Taylor et al. A strain-adaptive remodelling algorithm was used to predict the remodelling behaviour of the femur and tibia following TKA. Analysis was performed using ABAQUS. Virtual DEXA images were generated from the FE models at predetermined time-points, BMD gain and loss were also assessed both quantitatively and qualitatively.

Results: There was an increase and decrease in BMD for the femur and tibia models. BMD loss in the femur was predominantly experienced around the pegs and the distal femoral regions. Femoral BMD gain was displayed around the edges of the bone-implant interface, with higher activity at the anterior-medial and posterior-lateral aspects. BMD gain in the tibia was predominantly at the inferior end of the tibial tray’s keel, with the bone mass tending towards the medial aspect. Some bone gain was displayed on the medial side, surrounding the pegs and at the cortex. There was BMD loss on the lateral aspect of the tibia.

Discussion: The adaptive bone remodelling algorithm has shown a good correlation with clinical findings. Reports of clinical and FE studies have shown that for cemented knees, most bone loss occurs at the distal femoral region, especially at the anterior aspect. It has been reported that in the tibia there is generally an over-all decrease in BMD in the proximal tibia and increase below the keel. This is in accordance with our predictions. BMD gain was found to be more predominant on the medial aspect. This may be due to the more medially inclined loading ratio, which affects the stress distribution within the bone. BMD gain in the tibia is shown to follow a path, which starts at the bottom of the keel and tends medially towards the tibial cortex. This illustrates the inherent tendency of load transfer to follow along the stiffest structural path.