Effect of total knee replacement design and surgical technique on patello-femoral joint performance: an explicit finite element study

There is an increasing demand for total knee replacements (TKR). Young patients are placing increasing functional demands on modern TKR. Clinical experience has also shown the need for high flexion in patients after TKR. In this study, assessment of TKR performance subjected to deep knee bend was investigated. Patellar resurfacing in TKR is assumed to release pain and restore knee function. Despite the recent advance and success in TKR operation, patellar resurfacing has been associated with an increase in complications at the patello-femoral joint, and hence revisions following TKR. Complications include poor tracking, instability, wear, loosening and fractures. These complications have been attributed in part to the component design features (e.g. sagittal radius, depth, and orientation of the trochlear groove of the femur and the geometry of the patellar component surface) and surgical technique (e.g. component alignment and ligament balance). However, the influence of these factors on the overall performance of TKR has not been investigated extensively. The objective of the study was to determine the variation of patellar kinematics (tracking motion) and contact mechanics (contact force, area, pressure and stress) induced by component design and surgical technique. A three-dimensional finite element (FE) model of a PFC-Sigma TKR, including the tibio-femoral and patello-femoral joints was developed. Explicit FE analysis was used to simulate TKR under a deep knee flexion. The models predicted substantial increase in patellar pressure and stress with nonconforming patello-femoral articulating surfaces. Femoral groove orientation affected patellar tracking and contact mechanics. Extending femoral groove distally reduced patello-femoral contact stress at high flexion angles. Also, externally rotating the femoral component and adjusting the line of action of quadriceps pull would be beneficial by reducing patellar lateral force. The FE model used in the current study provided insight into the effect of component design parameters and surgical technique on patellofemoral kinematics and contact mechanics.

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