Collagen type type II destruction was studied after induction of experimental OA by ACL-transection in the rat. Damage was investigated by analysis of type II collagen neoepitope expression. Cleavage of type II collagen by collagenases (MMP’s) was detected by the Col2-3/4C-short antibody and collagen denaturation by Col2-3/4m. Rats were sacrificed after 2, 7, 14, 28 and 70 days. Immunostaining was performed using the Col2-3/4C (Collagenase-cleavage site) or the Col2-3/4m antibody (denatured type II collagen).

The first changes after the ACL-transsection were chondrocyte death at the margins of the articular cartilage of both tibia and femur. At day seven a pannus-like tissue protruded from the synovial tissue over the dead cartilage. Underneath the pannus-like tissue a marked staining for the collagenase-cleavage site was observed. The dead cartilage was replaced by fibrocartilage within 4 weeks after which the staining for the collagenase cleavage neoepitope had completely disappeared.

In contrast with the peripheral cartilage, in the central part of the medial tibia and femur dead chondrocytes were found on week 2 until the last time point examined, which was not replaced by fibrocartilage in this timespan. In these areas, loss of proteoglycans, fibrillation of superficial cartilage and staining for denatured type II collagen was found. Both cartilage damage and staining for denatured collagen increased with time. Only light collagenase cleavage site staining was observed on all time points in this central location.

OA in rats after ACL-transsection can be divided in two stages. An early phase lasting about 4 weeks, in which chondrocyte remodelling of the dead cartilage follows death at the cartilage margins. In this phase marked degradation of type II collagen by collagenases occurs. The second phase, characterised by cartilage damage in the central tibia and femur, shows increased staining for denatured type II collagen but little staining for the collagenase cleavage neoepitope.