The movement of the knee studied by magnetic resonance imaging

The author's work using magnetic resonance imaging to study the relative movements (the kinematics) of the tibia and femur is reviewed. The description is understood best by reference to comparative anatomy and by dividing the flexion are into three components. Knee activities take place mainly between 10degrees and 120degrees. Over this arc, the articulating surfaces of the femoral condyles are circular in sagittal section and rotate around their center. The medial condyle does not move anteroposteriorly (rollback does not occur medially). The lateral condyle tends to roll back producing tibial internal rotation with flexion. From full extension to 10degrees to 30degrees tibial internal rotation is coupled with flexion. The articulating surfaces medially are a larger radiused anterior femoral facet, which articulates with an upward-sloping tibial facet. Laterally, the femoral condyle rolls forward onto the anterior horn. Flexion beyond 120degrees only can be achieved passively. Medially, the femur rolls up onto the posterior horn. Laterally, the femur and the posterior horn drop over the posterior tibia.