Synovial chondromatosis

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)