Classification of osteochondritis dissecans

Stage	Plain radiograph findings	Magnetic resonance imaging findings	Arthroscopic findings
I	Depressed osteochondral fragment	Articular cartilage thickening and low signal changes	Irregular and softened articular cartilage with no fragment
II	Osteochondral fragment attached by an osseous bridge	Articular cartilage breached, low signal rim behind fragment representing fibrous attachment	Articular cartilage breached with definable fragment that is not displaceable
III	Detached, nondisplaced fragment	Articular cartilage breached, high signal changes behind fragment indicating synovial fluid between fragment and subchondral bone	Articular cartilage breached with definable fragment that is displaceable but attached by overlying articular cartilage
IV	Displaced fragment	Loose foreign body	Loose foreign body

Data from:

DeLee JC, Drez Jr D, Miller MD. DeLee & Drez's Orthopaedic Sports Medicine Principles and Practice, 2nd ed, Elsevier Science, Philadelphia 2003.
Dipaola JD, Nelson DW, Colville MR. Characterizing osteochondral lesions by magnetic resonance imaging. Arthroscopy 1991; 7:101.
Guhl JF. Arthroscopic treatment of osteochondritis dissecans. Clin Orthop Relat Res 1982; :65.

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