444 THE JOURNAL OF BONE AND JOINT SURGERY SYNOVIAL CHONDROMATOSIS OF THE KNEE IN CHILDHOOD A REPORT OF TWO CASES

Synovial chondromatosis is a rare metaplastic condition affecting major synovialjoints. It is extremely rare in childhood. The two children reported here are believed to be the youngest patients with this condition affecting the knee to have been described in the literature. Synovial chondromatosis is a rare condition characterised by the formation of chondro-osseous bodies in the synovium and subsynovial connective tissue of affected structures, usually major synovial joints (Lichtenstein 1977). The knee is the most commonly affected joint. The condition is invariably monarticular, and affects adults in their third, fourth and fifth decades (Jeffreys 1967). The aetiology of this condition is unknown, but the pathogenesis has been well described (Aegerter and Kirkpatrick 1975; Lichtenstein 1977; Dahlin 1978). Loose bodies are the end-result of a metaplastic error of synovial cells. Microscopic masses of chondroid begin to appear, usually in the tips of synovial villi. The surrounding cells alter to resemble chondroblasts. These cartilage aggregations grow, producing spherical bodies with the villi as their pedicles. Eventually they may detach to become free bodies in the joint space, the cellular elements in these loose bodies being nourished by synovial fluid so that they can continue to grow. Cellular metaplasia may occur with the appearance of osteoblasts and a bony nidus may form. Hundreds of loose bodies may occur in this manner (Aegerter and Kirkpatrick 1975). On review of the literature, it seems that the two cases presented here are considerably younger than any previously reported involving the knee