Effects of contact stress on patellarfemoral joint and quadriceps force in fixed and mobile-bearing medial unicompartmental knee arthroplasty
Background Unicompartmental knee arthroplasty (UKA) is an effective treatment for end-stage, symptomatic unicompartmental osteoarthritis of the knee joint. However, patellofemoral joint degeneration is a contraindication to medial UKA. Therefore, the objective of this study was to evaluate the biomechanical effect of medial UKA using fixed-bearing (FB) and mobile-bearing (MB) design prostheses on the patellofemoral joint. Methods A three-dimensional finite-element model of a normal knee joint
... normal knee joint was developed using medical image data. We performed statistical analysis for each model. The differences in contact stress on the patellofemoral joint and the quadriceps force between the FB and MB designs were evaluated under a deep-knee-bend condition.Results At an early flexion angle, the results of contact stress showed no significant difference between the FB and MB medial UKA models and the intact model. However, at large flexion angles, we observed a significant increase in contact stress with the FB models. On the contrary, in the case of the MB models, we found no statistically significant increment compared with the intact model. Our results indicate that with medial UKA, the contact stress increased and greater quadriceps force was applied to the patellofemoral joint. However, performing UKA on a patellofemoral joint with osteoarthritis should not be difficult, unless anterior knee pain is present, because the increase in contact stress is negligible. Conclusions Our results show no significant difference in contact stress on the patellofemoral joint between the medial UKA and intact knee joint models. Such a mechanism was easily found in MB medial UKA. Therefore, this study biomechanically showed that degenerative changes in the patellofemoral joint should not be considered an absolute contraindication to treatment with medial UKA.