Degenerative mechanism of articular cartilage induced by low stress. A morphological study.

Immobilization leads not only to diminished joint movement but also low stress of articular cartilage. The present investigation was undertaken to observe the morphological changes which arose in articular cartilage with low stress. The joint motion remained intact. Articular cartilage from the left knees of 66 rats whose left calcaneal tendons had been transected was examined under transmission electron microscope and light microscope. The degenerative changes were observed: decreased functional activity of chondrocytes progressively degenerated cartilage and lack of compensatory proliferation of chondrocytes at the early stage. We propose that the degeneration of articular cartilage induced by immobilization is the result of combination of low stress and lack of joint motion. The following degenerative mechanism begins with chondrocytes. Chondrocyte and matrix influence each other in a vicious cycle. Low stress may restrain the repair activities.