An unusual presentation of synovial chondromatosis of the knee in a 10-year-old girl.

Synovial chondromatosis commonly occurs in the anterior compartment of the knee joint, predominantly in middle-aged men. It is relatively unusual in female children and is rarely encountered in the synovium beneath the meniscus. The present report describes a rare case of synovial chondromatosis that developed in the synovium just inferior to both menisci of the right knee in a 10-year-old girl. At this unusual age and location, there is a greater probability of missed diagnosis, due to the lack of definite informative incidence, and difficulty in finding the lesions during arthroscopic examinations. In the present case, multiple loose bodies were hidden by the meniscus, and thus, there were no structural abnormalities in the initial arthroscopic views before probing the meniscus. After careful inspection, we found numerous cartilaginous loose bodies and removed them as much as possible with arthroscopy.