Bearing movement after Oxford unicompartmental knee arthroplasty: a mathematical model

Movements of the meniscal bearing on the tibial plateau after Oxford knee arthroplasty (Biomet Orthopedics, Inc, Warsaw, Ind) reflect tibiofemoral movement. They have been shown to be load dependent. This article describes the use of a mathematical model of the knee in the sagittal plane to show that movement differences under load are caused by differences in ligament strains induced by different combinations of external loads and muscle forces. During passive flexion, roll-back of the femur on the tibia is required to minimize the forces transmitted by the ligaments.