Glycosaminoglycan metabolism in experimental osteoarthritis caused by immobilization. The effects of different periods of immobilization and follow-up.

Glycosaminoglycan metabolism at different developmental stages of osteoarthritis provoked by immobilization was studied in rabbits. Tissue concentrations and the specific radioactivity of glycosaminoglycans (GAG) after a long immobilization (IZ) period (12 weeks) without follow-up, and a moderate IZ time (4-7 weeks) with a long follow-up period (average 22 weeks) were compared with the results obtained after a short IZ time (17 days). In tibial weight-bearing cartilage the specific 35S-activity had increased and the galactosamine, glucosamine and uronic acid concentrations had decreased in all the IZ groups examined. In the marginal cartilage, the menisci and the collateral ligament, the specific radioactivity and GAG concentrations had decreased or were normal after a long IZ with or without follow-up, although they were markedly elevated after a short IZ time. THe depletion of GAG correlated roughly with the IZ and follow-up times, except for periodically immobilized rabbits. In long-term "chronic" disease the specific radioactivities and GAG concentrations were depressed on the contralateral, non-IZ sides. The changes in the non-IZ knee are discussed. In studies of experimental osteoarthritis it is important to determine the developmental stage of the disease to be studied.