Despite the theoretical advantages of mobile bearings for lateral unicompartmental knee replacement (UKR), the failure rate in the initial published series of the lateral Oxford UKR's was unacceptably high. The main cause of failure was early dislocation. In contrast, dislocations of bearings in medial UKR's are rare. The lateral compartment present a higher laxity in flexion than the medial. An adaptation of the lateral design by introducing a convex tibial component and biconcave bearing should tackle this difference in kinematics. The risk of dislocation increased substantially if the lateral tibial joint line was elevated, quantified by the proximal tibial varus angle. This angle had a significant relationship to dislocation. A recent kinematic study identified roughly 3 times as much posterior translation of the tibia during deep knee bend activities after lateral UKR compared to the normal knee, possibly also resulting in a higher incidence of bearing dislocation. With the exception of dislocation, the overall early complication ratio in the initial published series of lateral Oxford UKR was also rather high compared to the last published series. Is there a learning curve? Between January 2009 and April 2010, 16 domed lateral Oxford unicompartmental knee replacements were implanted by the senior author. The valgus deformity was in 2 cases not completely correctable. All femoral components were positioned anatomically. In no case the popliteus tendon was divided. A partial iliotibial band (ITB) release was done in 2 cases. The most common tracking deviation of the bearing peroperatively was a small lift off in deep flexion, seen in 6 cases.Introduction
Materials and Methods
