Synovial chondromatosis of pes anserine bursa secondary to osteochondroma

Osteochondromas are common benign bone tumors. Synovial chondromatosis is a benign cartilaginous metaplasia that occurs in the synovium. The authors describe a unique case of synovial chondromatosis developing in the pes anserine bursa secondary to an underlying osteochondroma of the proximal medial tibia. It is unusual to see both of these processes occurring simultaneously in 1 location. After appropriate consent was obtained, the patient's case was reviewed. A 17-year-old boy presented with a painless mass in the medial aspect of the right leg. Initial imaging of the right leg showed a cartilaginous-appearing lesion arising from the tibia and several distinct additional cartilaginous masses in the adjacent soft tissue. After 16 months of observation, the patient began to have increasing pain in the region of the lesion. The patient underwent surgery for excision of suspected synovial chondromatosis of the right pes anserine bursa and osteochondroma of the proximal right tibia. Postoperatively, the patient had complete resolution of symptoms and regained full range of motion of the knee. He returned to full activities, including walking and running. Osteochondromas are common benign bone tumors. Synovial chondromatosis is a benign synovial metaplastic cartilaginous proliferation that occurs primarily in joints, but can occur in any synovial-lined space. In this case report, the authors describe a unique occurrence of both of these lesions simultaneously. The treatment was excision of the osteochondroma and resection of the chondromatosis lesions, which resulted in an excellent outcome.