Knee specimens were placed in an apparatus which imposed cyclic
anterior-posterior or rotatory forces, with various compressive loads
applied to the joint. Force-displacement graphs or torque-rotation graphs
were automatically plotted, giving the laxity under various conditions. The
ligaments, capsule, and menisci provided joint stability under no-load
conditions. However, under compressive loads, the conformity of the
condylar surfaces was an important factor in stabilizing the knee. The
mechanism proposed was the uphill movement of the femur as the femur and
the tibia were displaced or twisted relative to one another.