Introduction
- Also known as synovial chondro-metaplasia
- Rare condition of unclear etiology in which foci of cartilage develop in the synovial membrane of joints, bursae, or tendon sheaths as a result of metaplasia of the subsynovial connective tissue
- Nodules can detach and become loose bodies within the joint, which may undergo secondary calcification and ossification
- Extra-articular involvement may occur if proliferating loose bodies break through joint capsule or if synovial structures outside joint (eg, tendon sheaths, bursae) are involved
- Generally a primary condition, but may occur secondary to osteoarthritis
- Most often arises in weight-bearing joints of the lower extremity (hip, knee); usually monoarticular involvement
- In upper extremity, shoulder, elbow, wrist, and small joints of hand may be affected
Tumor biology and incidence
- Benign periarticular cartilaginous lesions
- May be calcified and/or ossified
- Not known to metastasize but may give rise to intra-articular loose bodies
- Extremely low risk of malignant transformation to chondrosarcoma
Age
Primarily adults in their 20s through 40s
Gender
M:F = 2:1
Presentation
- Joint pain, swelling, stiffness
- Patient may report history of slowly progressing symptoms: clicking, locking, or catching sensation during joint range of motion
- Baseline dull, aching discomfort exacerbated by motion, causing sharp pain
Physical findings
- Locked joint or limited range of motion (10-15 degree loss of flexion/extension)
- Joint effusion
- Possible inflammatory signs
- Compare to contralateral side, noting fullness, effusion, palpable loose bodies in synvovial recesses, and medial/lateral joint line tenderness
Plain films
Site
- Knee most commonly involved
- Hip, shoulder, elbow, and ankle also involved
- May affect any joint bursa or tendon sheath
Size
- Multiple calcified bodies in joint; regular in outline and uniform in size
- Range from a few millimeters to several centimeters.
Tumor effect on bone
- Some individual lesions may extrinsically erode underlying surface of bone and articular cartilage
- May progress to cause degenerative arthritis
Bone response to tumor
Mild reactive sclerosis may result from bone erosion
Matrix
- Lesions composed of cartilage matrix
- Variable degrees of calcification and/or ossification
Cortex
Not applicable
Soft tissue mass
Lesions frequently extend into bursae around distended joints




CT scan
CT scan can demonstrate an effusion, a mass effect with radiolucent loose bodies, or multiple calcified and or ossified loose bodies

MRI
- Variable findings depending on relative amounts of synovial proliferation and calcified nodule formation
- Loose bodies tend to have low signal on T1-weighted images and high signal on T2-weighted images
- Lesions with extensive calcification may have low signal on all images


Classification (Milgram)
- Early: Chondrometaplasia but no loose bodies
- Transitional: Synovial disease and loose bodies
- Late: Loose bodies predominate generally with extensive effusion
Differential diagnosis
- Any source of loose bodies (secondary osteochondromatosis), such as osteochondral fracture, osteoarthritis, neuropathic joint, or osteochondritis dissecans
- Synovial chondrosarcoma
- Myositis ossificans
- Pigmented villonodular synovitis
- Septic joint
- Calcific tendonitis (shoulder)
- Soft tissue chondroma (hand),
- Saponification of patellar fat pad (anterior knee)
- Osteogenic sarcoma
- Myxoid chondrosarcoma (posterior knee)
Natural history
- Generally benign, self limiting disease
- However, can become disabling, resulting in secondary degenerative osteoarthritis
Pathology
- Gross: Thickened, nodular synovium often with separate loose bodies of chondroid-appearing tissue
- Microscopic: Nodules of chondroid tissue within synovium
- Cartilage may be cellular but cells are in clusters
- May be variable mineralization
- Differentiation into trabecular bone may be present

Diagnosis and treatment
- Diagnosis may be made radiographically
- Plain radiographs may be normal and may require further investigations – such as arthrogram, MRI, or arthroscopy – to make diagnosis
- Treatment is controversial
- Removal of loose bodies can be done with or without total synovectomy
- Alleviates symptoms and prevents secondary joint changes
- Low risk of recurrence (<20%).
- Some clinicians prefer complete synovectomy
- More extensive than removal of loose bodies
- May be associated with increased morbidity (eg, arthrofibrosis)
- May have lower recurrence rate than removal of loose bodies
Surgical findings



Complications
- Recurrence
- Loss of range of motion
- Arthrofibrosis
- Arthritis
- Transition to synovial chondrosarcoma (rare/associated with multiple recurrences)
Recommended reading
OKU Musculoskeletal Tumors AAOS 2nd Edition 2007, Ch 28 pg 265-266.
Adelani et al. Benign Synovial Disorders. JAAOS, Vol 16, No 5, May 2008, 268-275
Sperling et al. Synovial chondromatosis and chondrosarcoma: a diagnostic dilemma. Sarcoma. 2003;7(2):69-73.
Maurice et al. Synvovial Chondromatosis JBJS Br 1988; 70(5): 807-11.
Sah et al. Malignant Transformation of Synovial Chondromatosis of the Shoulder to Chondrosarcoma*.* A Case Report. JBJS Jun 2007;89:1321-1328.