Primary synovial chondromatosis: a clinicopathologic review and assessment of malignant potential

This is a clinicopathologic review of 53 cases of primary synovial chondromatosis covering a period of 30 years. The average age at presentation was 41 years (range, 17 to 64 years) with a male/female preponderance of 1.8:1. The condition was always monarticular, the most common site being the knee joint (70%) followed by the hip (20%). Degenerative joint disease was well established in three patients (5%), all occurring in the hip. Nine patients suffered recurrences (15%), including three that became malignant. There was no relationship between the age and site of the lesion, nor between the degree of cellularity of the cartilage and age or site. However, there was an association between cellularity of the cartilage and the extent of calcification and ossification--highly cellular lesions were poorly calcified and ossified, but heavily calcified lesions were usually of relatively low cellularity. There was no relationship between extent of calcification and ossification and the age of the patient. Three patients suffered malignant change representing a relative risk of 5%, much higher than that quoted in other series. This suggests that primary synovial chondromatosis has a significant potential for malignant change.