General
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• Also called synovial chondrometaplasia, synovial osteochondromatosis
• Mean age 41 years, range 17-64 years, 2/3 male (Hum Pathol 1998;29:683)
• Primary disease is uncommon, unknown etiology, aggressive (Hum Pathol 1979;10:439)
• Usually monoarticular, can be bilateral rarely (JCDR 2012;6:475), affecting knee, hip, elbow and communicating bursae; may affect adjacent soft tissue
• Aggravated by infection and trauma
• May be extra-articular (tenosynovial chondromatosis)

Radiology
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• Xray: usually calcific densities within joint; may be negative or show diffuse joint swelling

Case reports
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• 11 year old girl with persistent left elbow pain 2 months after roller skating accident (Indian J Orthop 2011;45:181)
• 13 year old girl with progressive swelling over thumb (Hand (N Y) 2012;7:98)
• 26 year old man with chronic bilateral ankle pain (Chiropr Osteopat 2007;15:18)
• 32 year old man with unilateral spinal claudication and tenderness of sacroiliac joint (Acta Orthop 2011;82:246)
• 36 year old man with knee pain (Sports Med Arthrosc Rehabil Ther Technol 2009;1:6)
• 36 year old woman with pain and swelling in both knee joints (IJHSR 2012;2:87)
• 49 year old man with progressively worsening knee pain (J Med Case Rep 2010;4:113)

Treatment
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• Excision, but frequently recurs; 5% become malignant

Clinical images
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Loose bodies in synovial chondromatosis

Multiple loose osteocartilaginous fragments

Smooth white nodule

Showing extent of disease

Gross description
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• Numerous round osteocartilaginous nodules cover a thickened synovial surface or float freely within joint space

Micro description
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• Cartilage cells with variable atypia or binucleated forms within synovium; clusters of chondrocytes are often arranged in lobules; no underlying arthritis

Micro images
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Metaplastic cartilage in synovium

Clusters of chondrocytes

Resembles Grade 1 chondrosarcoma

Nodule of cartilage

Lobular structure

Medium power

Loose bodies

Subsynovial cartilaginous nodule

Moderate atypia of chondrocytes

 

Osteochondral loose body

Cartilaginous tissue enclosed by synovial tissue

Differential diagnosis
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• Cartilaginous loose bodies: more common, but associated with arthritis
• Chondrosarcoma: not within a joint, no characteristic clustering pattern, marked myxoid change, spindling of nuclei
• Injury-related soft-tissue calcification
• Lipoma arborescence with osseous metaplasia
• Neuropathic arthropathy or osteochondritis dissecans: no lobulation, clustering or atypia
• Pigmented villonodular synovitis
• Secondary synovial chondrometaplasia due to degenerative joint disease
• Synovial vascular malformation

General
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• Associated with degenerative joint disease - growth of fragments of articular cartilage
• Initially intrasynovial disease without loose bodies; then intrasynovial proliferation and free loose bodies, then multiple free osteochondral bodies without intrasynovial disease
• No atypia

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