Reversibility of joint changes produced by immobilization in rabbits.

Rabbits knee joints which had been immobilized for only 2 weeks regained motion during the first 2 months of remobilization. Histologically, joint tissues were normal. Only 9 of the 14 rabbits immobilized for 6 weeks regained normal or partial knee motion. Animals that regained knee motion generally did so during the first 4 months of remobilization. There are 2 types of repair of the damaged cartilage; replacement by fibrocartilage and proliferation of chondrocytes. Normal chondrocyte alignment and normal collagen fibril orientation was not restored. Repaired cartilage did not withstand normal joint stress.