Computer-assisted analysis of ligament constraints in the knee

A computer graphics technique was employed to investigate the ligament constraints in the knee joint. A computer-assisted tomography scan system was employed to obtain the geometry of the knee and the ligament insertion locations. A cadaver knee was mounted in a special rig that kept the femur and the tibia in a specified position. The scans of the knee at 5-mm distances were recorded. These scans were projected in the computer to generate a data base for the tibia, the femur, and the tibial and femoral insertion locations for the various ligaments. The computer graphics analysis provides realistic views of the bone structures. The views compare favorably with the original CT scans. Interestingly, the scans near the ligament insertion site were clearly observed to have a higher bone density. Higher density was also observed at the intercondylar notch below the patella. The analysis was used to simulate ACL and PCL insufficiencies. A Lachman test at 25 degrees of flexion is a sensitive test for ACL insufficiency, whereas the 90 degrees drawer test may not be a sensitive indicator of PCL insufficiency. This computer graphics technique may prove useful in the design and development of artificial ligaments as well as in planning surgical procedures.