OBJECTIVETo compare the knee osteoarthritis (OA) models in rabbits by different concentrations of papain and provide data for exploring pathogenesis and treatments of this disease.

METHODSSixty New Zealand white rabbits were randomly divided into four groups of 15 each and given injections into the right knee on days 1, 3 and 5 including intra-articular injections of 2%, 5% or 10% (w/v) papain and 0.03 mol/L L-cysteine at the dose of 0.1 ml/kg (experimental groups). The 0.9% NaCl (w/v) with a dose of 0.1 ml/kg were injected intra-articularly into the right knees of rabbits in the control group. The rabbits were sacrificed at 2, 4, 6 weeks respectively after the initiation of papain injection and these OA models were evaluated through recording the width of knee joint, performing the morphological observation and histological evaluation of articular cartilage and synovium.

RESULTSThe degenerative changes were demonstrated in knee joints of rabbit in all experimental groups, such as thinner articular cartilage, fibrillation and destroyed cartilage matrix, and inflammation, proliferation, and degeneration of the synovial tissue. All these changes were much worse with increased concentration and prolonged observation time.

CONCLUSIONDifferent severity of OA are established through intra-articular injections of 2%, 5% or 10% papain and 0.03 mol/L L-cysteine at the dose of 0.1 ml/kg. These models are of the characters of short period and a good reproducibility.