Hydroxyapatite deposition in osteoarthritic articular cartilage of the proximal femoral head.

Hydroxyapatite crystal deposition in the articular cartilage of the proximal femoral head was examined by using light and electron microscopy and electron probe microanalysis. The hydroxyapatite deposition was significantly more frequent in patients with osteoarthritis (40.7%, 22 of 54) than in control subjects (6.0%, 3 of 50) (P less than 0.001). Initial deposition of needle-like crystals was always seen on or within the electron-dense, amorphous material around the degenerating hypertrophic chondrocytes. Matrix vesicles were rarely seen in the calcifying areas.