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.

The purpose of this study was to determine which activities are important to patients and to determine the severity of those problems. The five most important activities were walking outside, driving, walking indoors, stair climbing and daytime pain. Importance of these did not change postoperatively. The five most severe problems causing limitation were a limp, stiffness, loss of energy, daytime pain and locking. All these activities become statistically less severe over twenty-four months. Activities that are important to patients are different than the problems that are ranked by severity. Surgeons can educate patients that the severity of problems do improve over time following TKA.

The objectives of this study were:

to determine the five most important activities and five most severe problems for patients prior to total knee arthroplasty (TKA) using the Patient Specific Index (PASI) and

Activities that are most important to patients are different than problems that patients find severe. Important activities remain important over time. Severe problems become less severe over time.

Functional activities and PASI scores improve after TKA. Surgeons can educate patients that the problems they find most severe preoperatively do improve over time following TKA. Important activities remain important.

Patients scheduled for elective primary (or revision) TKA at two tertiary care teaching hospitals were enrolled in the study, excluding those not fluent in English and those undergoing TKA for a tumour, acute fracture, or an infection of the prosthesis. Patients completed the PASI pre-operatively, six, twelve and twenty-four months post-operatively.

One hundred and nineteen subjects were enrolled, nineteen were excluded. The five most important activities (ten- point scale, ten is most important) preoperatively were (mean; 95% CI): walking outside (6.25; 6.23–6.27), driving (6.17; 6.12–6.22), walking indoors (6.14; 6.12–6.16), climbing stairs (6.12; 6.10–6.14), and daytime pain (5.84; 5.81–5.87). These activities were not statistically less important over time. The most severe problems were limping (4.81; 4.77–4.85), stiffness (4.59; 4.56–4.62), lack of energy (4.51; 4.47–4.55), daytime pain (4.46; 4.43–3.39) and locking (4.38; 4.27–4.49). These were significantly less severe at twenty-four months (p < .001).