Observations of reversibility of glycosaminoglycan depletion in articular cartilage.

Observations of reversibility in the surface depletion of glycosaminoglycans in articular cartilage after experimental surgical operations focussed attention on whether the depletion always leads to osteoarthritis or may be an early nonspecific response of articular cartilage to differing injuries. Histologic sections obtained from the patellae of 42 rabbits were investigated at different postoperative intervals. On sections stained metachromatically with Toluidine blue at pH 3, visual measurement by light microscopic examination as well as measurement of optical density, were performed to estimate the degree of surface depletion of glycosaminoglycans. In addition, the glycosaminoglycan level in the areas below the depleted zones was measured by optical densitometry. The results obtained by both methods demonstrated a marked depletion of glycosaminoglycans one week after surgery, reaching a maximum after four weeks. Subsequently, significant decreased depletion continued until 26 weeks. The mean level of glycosaminoglycans was always lower than normal. Concurrent with the surface depletion of glycosaminoglycans were histologic signs of synovitis. Reversible surface depletion of glycosaminoglycans may occur in articular cartilage with normal morphology. It presumably represents a nonspecific reaction of cartilage as well as an early sign of osteoarthritis before "the state of no return."