Type II collagen degradation in articular cartilage fibrillation after anterior cruciate ligament transection in rats

Objective: To investigate the kinetics of early cartilage changes in mechan ically induced osteoarthritis (OA) and the association of these chances wit h damage to the type II collagen network. Methods: Experimental OA was induced by anterior cruciate ligament transsec tion in the rat knee joint (ACLT-OA). Animals were sacrificed after 2, 7, 1 4, 28 and 70 days. Knee joints were evaluated using routine histology and i mmunohistochemistry for denatured (unwound) type II collagen to detect coll agen damage. An antibody recognizing the collagenase cleavage site in type II collagen was used to study the role of collagenase in this process, Results: The first changes of the articular cartilage after anterior crucia te ligament transection occurred in the superficial zone. These changes inc luded loss of superficial chondrocytes, swelling of the remaining chondrocy tes and superficial fibrillation. The swelling of the chondrocytes did not result from a change towards the hypertrophic phenotype, since these cells did not stain for type X collagen. A marked increase in denatured type II c ollagen staining was present in the fibrillated areas, Staining of the coll agenase cleavage site showed the same distribution as denatured collagen bu t was clearly less intense. Collagen damage could never be detected before fibrillation occurred and was not present in non-fibrillated areas. Conclusions: These results indicate that in this model cartilage degenerati on starts at the articular surface and that this degeneration is associated with a localized expression of type II collagen degradation products. (C) 2001 OsteoArthritis Research Society International.