Review Question - QID 219396

Figure A demonstrates multiple spheroidal calcific densities in the knee joint, which are pathognomonic radiographic findings of synovial chondromatosis, a benign metaplastic disease of synovial tissue (Answer 5).

Synovial chondromatosis (SC) is a rare, benign condition resulting from metaplastic changes in synovial tissue. Characteristically, the synovium undergoes metaplasia, forming cartilaginous nodules that break free, mineralize, and eventually ossify intra-articularly or extra-articularly. The knee is the most common location for SC, followed by the hip, shoulder, elbow, ankle, and wrist. The presentation may be nonspecific and even asymptomatic, but symptoms often include pain, swelling, decreased range of motion, and crepitus. Diagnosis can be made on radiographs featuring multifocal, spheroidal calcific densities. However, 20% of SC cases do not present with radiographic findings due to time-dependent mineralization of the loose bodies. MRI is a useful imaging tool for the early stages of SC. Treatment for symptomatic cases requires open or arthroscopic removal of loose bodies, with the role of complete synovectomy being debated. Recurrence can occur in up to 30% of patients, and untreated SC may lead to articular destruction and chronic pain.

Neumann et al. provide a comprehensive review of synovial chondromatosis, a rare benign condition featuring the formation of cartilaginous nodules within synovial joints, tendon sheaths, or bursae. The authors note the metaplastic origins of SC, lacking cellular atypia or invasion. Radiographical diagnosis may be challenging, given the various stages of mineralization and calcification of the loose bodies. Therefore, the authors recommend MRI to confirm the diagnosis in the early stages of the disease. The authors prefer arthroscopic treatment for most cases with optional synovectomy to prevent recurrence. Emphasis is placed on early and accurate diagnosis and intervention to prevent periarticular destruction.

Chaudhary et al. published a case report of extra and intra-articular synovial chondromatosis. The first case was a 25-year-old female with intraarticular synovial chondromatosis of the knee, causing significant loss in range of motion and pain. This patient underwent arthroscopic removal of the intraarticular loose bodies and subsequently had a significantly increased range of motion. The second case was a 22-year-old male with extra-articular synovial chondromatosis of the distal femur with significant pain and quadriceps wasting. This patient underwent open excision of the extra-articular cartilaginous masses, which was confirmed to be synovial chondromatosis on histopathologic examination. The authors report that extra-articular synovial chondromatosis is a rare finding but should be treated with open excision and complete excision of the involved bursa.

Figure A shows the AP and lateral of a left knee with multiple calcified nodules with the synovial space, consistent with synovial chondromatosis.

Incorrect Answers:
Answer 1: Synovial chondromatosis affects the knee in 70% of cases, the hip in 20%, and the shoulder, elbow, ankle, and wrist in the remaining cases.
Answer 2: Although the loose bodies typically occur in synovial joints, SC has been known to occur extra-articularly in tendon sheaths or bursae. Loose bodies may escape through the joint to extra-articular locations or can primarily form in the tendon sheath or bursa.
Answer 3: Monosodium urate crystal deposition is the pathophysiology of gout. Like SC, gout is an intraarticular disease that may eventually cause periarticular erosions. However, gout will not feature calcified loose bodies as seen in Figure A.
Answer 4: Overexpression of the CSF1 gene is the pathophysiology of pigmented villonudular synovitis (PVNS). PVNS is a locally aggressive synovial disease, but unlike SC, it will not feature the calcified loose bodies as seen in Figure A.