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The relation between prosthesis component kinematics and posterior slope of the tibial component in total knee arthroplasty is much debated. Three-dimensional kinematics of the replaced knee was obtained by video fluoroscopy in 23 knees treated by cruciate-retaining or cruciate-substituting arthroplasty. Relative position and orientation of the metal components were calculated in stair ascending, getting up from and sitting down on a chair, and single step up-and-down. Significant correlations were found between tibial component posterior slope and anteroposterior position of tibiofemoral lateral contact and between this slope and maximum knee flexion. These correlations were task and design specific. However, the average of the tibiofemoral contact positions over all three motor tasks was slightly posterior to the midline of the tibial base plate, reaching at most 84% of its anteroposterior dimension. Performing a posterior slope of the tibial cut does not put total knee arthroplasty with high conforming designs at higher risk of failure, even when large posterior inclinations need to be achieved.

The knowledge of cartilage wear patterns at the medial tibial plateau is important to understand the main causes of arthritis in varus knees. The most important factors influencing knee arthritis in fact seem to be the severity of the degenerative changes determined by the lower limb mechanical axis and the abnormal knee joint kinematics which frequently results from dysfunction of the anterior cruciate ligament.We studied the wear patterns of cartilage damage in 70 medial tibial plateaus resected at operation during total knee arthroplasty indicated for varus osteoarthritic knee. Anterior cruciate ligament and medial meniscus integrity was assessed intra-operatively. Calibrated digital images were used to measure the wear patterns with a standard software tool. The medial compartment of the tibial plateau was divided into six zones, and the amount of cartilage and bone destruction in each zone was classified into two grades.The wear pattern was found to be highly dependent upon knee varus deformity (Mann Whitney P0.001) and anterior cruciate ligament integrity (Friedman P0.0005). Anterior cruciate ligament was found intact in 35.7% of the cases. Wear patterns on intact anterior cruciate ligament knees occurred in the central to medial aspect of the tibial plateau. Anterior cruciate ligament deficient knees had significantly larger wear patterns anteriorly and posteriorly in the most medial region of the medial plateau.These observations suggest altered joint mechanics exist in anterior cruciate ligament deficient varus knees, which would worsen cartilage degeneration and osteoarthritis progression.