Relation between knee motion and ligament length patterns

Fifteen knee specimens were tested in a 6°-of-freedom test machine using quadriceps force to drive continuous flexion-extension motion. Ten of the knees were again tested following isolated transaction of the anterior cruciate ligament. From transducer outputs, three-dimensional motion was determined. Using biplanar radiography and bone sectioning, ligament insertion coordinates and joint surface geometry were determined and used to calculate ligament length ratios as a function of knee flexion. Consistent motion patterns were seen in all knees. The prominent aspects of motion were a 15° internal rotation and an 8.6 mm anterior displacement of the tibia with flexion from 0 to 120°. Anterior cruciate transaction resulted in abnormal and excessive anterior-posterior displacement in early flexion, but a return to normal in late flexion. The results indicated that under our test conditions the boundaries of anterior-posterior motion were determined primarily by the cruciate ligaments, but tibial rotation was not guided by the cruciate ligaments.