Pathological study of the calcification of the hip joint

Calcification of articular tissue has been studied much since McCarty and others confirmed that pseudogout is caused by deposition of calcium pyrophosphate dihydrate (CPPD) crystals. However, there has been little attention paid to the hip joint in which detection of calcification is difficult because of the joint's deep location. In this study, arthritic hips were examined pathologically in relation to joint calcification. In cases of total hip replacement (THR), the rate of pathological calcification was 11.7 percent in osteoarthritis, 13.7 percent in rheumatoid arthritis and 22.2 percent in avascular necrosis of the femoral head. However, blood chemical examinations showed no abnormalities in parathyroid or kidney function, so these cases were classified as sporadic articular calcification. Macroscopically calcified hips were found in 11 percent of the autopsy cases. Articular calcification causing crystal-induced arthritis in cases with severe secondary coxarthrosis treated with THR occurred often. Calcified deposition was found in the articular cartilage as well as in the limbus, and even in synovial tissues. Light microscopy and scanning electron microscopy clearly demonstrated CPPD crystals. Infra-red spectrograms showed pyrophosphate crystals. In light microscopic observations, calcification in the articular cartilage appeared as granular accumulations of the crystals in the matrix of the surface and intermediate layers. Especially, the granular deposits were recognized in the marginal area of the chondrocyte lacunae in the intermediate layer. However, crystal deposits were seen along the fissures of collagen fibers in the surface and intermediate layer of the limbus. The crystals were square, rod or cube shaped, and 0.1-3.5μm×0.2-4.0μm in size, as were CPPD crystals detected previously.