Range of motion in total knee arthroplasty. A computer analysis.

A three-dimensional computer model of the knee was formulated based on sectional and coordinate data from knee specimens. The model was consistent with published data in terms of contact points and ligament length patterns. Prosthetic components were designed, and surgical placement was simulated. Maximum flexion was limited by tension in the posterior cruciate ligament. Increased dishing of the tibial surface reduced flexion, but some dishing was considered necessary for reduction of contact stresses. Anteroposterior translation of the tibial component had little effect on flexion. Femoral translation had some offset, and posterior positioning reduced flexion. The most important surgical variable was tibial component tilt in the sagittal plane. Posterior tilt increased motion, while anterior tilt decreased motion. The results apply to the choice of total knee system, instrument design, and surgical technique.