Primary
synovial chondromatosis (PSC) is thought to be a cartilaginous
metaplasia, but it may recur locally and malignant change has been reported. Histologically, the cartilage is usually cellular, with binucleate forms. These findings suggest that the disease is not simply a
metaplasia but imply a proliferative component. In this study, immunohistochemical detection of Ki-67
protein using an
antigen retrieval microwave heating technique and
DNA image cytometry (VIDAS image analysis system) has been used to assess the proliferative activity in 20 cases of PSC and the results have been compared with those obtained in other cartilage tissues: ten
enchondromas, ten
chondrosarcomas, and ten samples of normal articular cartilage. There was no detectable staining for Ki-67
protein in cases of PSC or in benign tissues, but there was a significant association between Ki-67 labelling index and grade in the
chondrosarcomas (P < 0.01). The absence of mitotic figures and the lack of Ki-67
protein in PSC are consistent with a
metaplasia. All
enchondromas gave diploid
DNA histograms but non-diploid histograms were obtained i eight cases (40 per cent) of PSC, with significant populations of hyperdiploid and
DNA aneuploid cells. The mean
DNA content, the percentage of hyperdiploid cells, the percentage of
DNA aneuploid cells, and the 2c deviation index were all significantly higher in PSC than in
enchondromas (P < 0.01). These findings with image cytometry suggest a proliferative process in the development of at least some cases of PSC. In terms of cell proliferative activity, PSC appears to occupy a position which is intermediate between benign
enchondromas and malignant
chondrosarcomas, which may explain the aggressive clinical behaviour occasionally seen in this condition.