Softening of canine articular cartilage after immobilization of the knee joint.

Using the indentation method, effects of immobilization with a splint for 11 weeks on the stiffness of the articular cartilage in the canine knee were investigated. Stiffness was determined for femoral, tibial, and patellar articular cartilages with nine, eight, and three test points, respectively, in the form of elastic moduli. Immobilization, without causing any macroscopic changes on cartilage surface, influenced the quality and quantity of articular cartilage. Immobilization caused significant softening of the femoral and tibial cartilages. The rate of deformation under the test load increased (42%) and the average thickness of the cartilage decreased (9%) as compared with the controls. Normal cartilage stiffness remained in the contact area between the patella and patellar surface of the femur, probably as a consequence of the sustained, but not forceful, loading between the femur and the patella produced by the flexion of the knee joint.