Immunohistochemical analysis of type X-collagen expression in osteoarthritis of the hip joint

Conflicting data have been reported on the spatial distribution of type X-c ollagen expression in osteoarthritis, and no concise data exist on a possib le correlation between type X-collagen expression and clinical and radiolog ical alterations. Well defined clinical and radiological data were compared with histopathological and immunohistochemical findings to investigate the expression of type-X collagen in osteoarthritis of the hip joint. Femoral heads were obtained in tote from 11 patients undergoing routine hip arthrop lasty for femoral neck fractures (n = 3) or osteoarthritis (n = 8) and from 13 patients (age: 12 days to 69 years) without any evidence of hip-joint p athology. Whole coronal sections from the femoral head were decalcified for routine histology and immunohistochemical analysis with use of type-specif ic monoclonal antibodies to type-X collagen. Our results demonstrate that t ype-X collagen is consistently found in osteoarthritic cartilage and is abs ent from normal adult cartilage (including the :region of calcified cartila ge). Except for the occurrence of type-X collagen in the middle zone of art icular cartilage in advanced stages of osteoarthritis, there is no specific change in the staining pattern or intensity for the collagen during osteoa rthritis, particularly when the staining is related to clinical and radiolo gical parameters. Hardly more than 20% of the extracellular matrix stained for type-X collagen; therefore, we suggest that, in most cases, this type o f collagen may not play a direct biomechanical role in the weakening of ost eoarthritic cartilage but rather may contribute indirectly to a disturbance of the disc biomechanics by altering matrix-molecule interaction. However, expression of type-X collagen may indicate a change in chondrocyte phenoty pe that consistently coincides with the formation of chondrocyte clusters, one of the first alterations in osteoarthritis visible on histologic examin ation.