A 60-yr-old woman presented to an orthopedic surgeon for evaluation of right knee pain. She had been experiencing pain for 10 yrs, and over the past 3 yrs, the pain increased in intensity. She also reported remote minor injury to the knee. Physical examination was significant for limited range of motion of the right knee with flexion to about 90 degrees. Manual muscle testing revealed mild weakness of the quadriceps muscle. Palpatory examination was difficult to appreciate because of patient's obesity. The x-ray of the right knee showed degenerative changes along with large calcified, lesions proximal to the patella (Fig. 1). Follow-up magnetic resonance imaging revealed two lesions in the suprapatellar pouch, the largest measuring 3.09 cm × 2.94 cm × 1.7 cm.
The patient underwent a one-stage total knee replacement and removal of the two large cartilaginous bodies. Interestingly, they were located extra-articularly, posterior to the quadriceps tendon surrounded by a pseudocapsule. In the postoperative period, she progressed well and was discharged home.
Synovial chondromatosis is a rare benign condition, characterized by metaplasia and formation of multiple cartilaginous nodules in the synovium of the joints, tendons, and bursae. Although the etiology is unknown, there are data suggesting neoplastic origin with chromosome 6 abnormalities.1 The proliferated fragments may break off from the synovial membrane and form loose bodies in the joint. In rare instances of synovial osteochondromatosis, the cartilaginous nodules may break through the joint capsule and proliferate extra-articularly.2
Often patients present with joint effusion, decreased range of motion, pain, or palpatory nodules. When these cartilaginous nodules calcify they become visible on radiography. Hence, x-ray is usually the diagnostic test of choice. Magnetic resonance imaging or computed tomography with arthrography is more sensitive for detecting noncalcified bodies and delineating the extent of disease. Arthroscopic removal of the loose bodies with partial synovectomy is both diagnostic and therapeutic and is the treatment of choice in most cases.3 However, in cases with extensive osteochondromatosis and extra-articular locations, open resection is indicated. Depending on the location there can be less restriction on range of motion, which could allow significant growth of the cartilaginous bodies and delay in the diagnosis of osteochondromatosis. Although rare, synovial osteochondromatosis, therefore, has to be considered in the differential diagnosis involving knee pathology.
1. Buddingh EP, Krallman P, Neff JR, et al: Chromosome 6 abnormalities are recurrent in synovial chondromatosis. Cancer Genet Cytogenet
2. Dunn W, Whisler JH: Synovial chondromatosis of the knee with associated extracapsular chondromas. J Bone Joint Surg Am
3. Wakhlu A: Synovial osteochondromatosis. J Indian Rheumatol Assoc