Immobilization ameliorates chemically-induced articular cartilage damage.

We have previously shown that immobilization protects against the development of mechanically-induced osteoarthritis following-anterior cruciate ligament transection in dogs. Herein, we examine the effect of immobilization of the leg on the chemically-induced degeneration of femoral articular cartilage caused by intraarticular injection of iodoacetate in guinea pigs. One week after the injection, cartilage from animals which were not immobilized exhibited a decrease in Safranin O staining and a 10-20% reduction in the number of chondrocytes. Three weeks after injection, cell death and loss of Safranin O staining had progressed, and surface fibrillation and osteophytes had developed. Articular cartilage from the contralateral (uninjected) knees of guinea pigs which received iodoacetate, and from knees of animals which were immobilized for 1 week but did not receive iodoacetate, was histologically and histochemically normal. However, specimens from 2 of 4 untreated knees which were immobilized for 3 weeks showed a reduction in Safranin O staining. Immobilization of the knee did not alter the loss of Safranin O staining seen after intraarticular iodoacetate injection, but did reduce the depletion of chondrocytes (P less than 0.05). Furthermore, neither osteophytes nor fibrillation developed in any of the animals which were constrained after iodoacetate injection. Thus, immobilization was clearly protective in this model of chemically-induced cartilage injury.