Early acetabular cartilage degeneration in a rabbit model of developmental dysplasia of the hip.

BACKGROUND Mild developmental dysplasia of hip (DDH) causes high morbidity of osteoarthritis (OA) on adult. It is thought that change of collagen and proteoglycans in cartilage may be the direct reasons for osteoarthritis. OBJECTIVE To detect the changes of the expressions of type II collagen of acetabular cartilage in early DDH and to investigate the relevance between type II collagen and the degeneration mechanism of the acetabular cartilage. METHODS The rabbit model of DDH was successfully established by applying the method of knee extending and fixing with cylinder cast in which left lower extremity as experimental group and right one as control group, checking with X-ray after 5 weeks. The stains of H&E and toluidine blue were applied on the samples of acetabular cartilage to observe the morphological changes of chondrocytes and extracellular matrix (ECM). The immunohistochemical staining and Western-blot were employed to respectively qualify and quantitate the expression of type II collagen. RESULTS Pathohistology observing indicated the signs of retrogressive changes of acetabular cartilage in experimental group. Also, the positive stained cells in type II collagen in experimental group was higher based on immunohistochemiscal staining. The quantitative amounts of type II collagen by Western-blot in experimental group was higher significant difference existed between two groups (t = 2.18, P < 0.05). CONCLUSIONS The expression of type II collagen is correlated to a degeneration of acetabular cartilage and increase obviously in early DDH.