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Osteochondritis dissecans (pronounced /??stio?k?n’dra?t?s ‘d?s??kænz/, often abbreviated to OCD) is a form of osteochondritis affecting the subchondral bone of joints, with harmful side effects on articular cartilage.[1] Physical trauma, avascular necrosis and other stresses may affect the subchondral bone, causing loss of support for adjacent cartilaginous structures.[2] This can lead to separation of a joint fragment from the underlying bone (hence the label dissecans which here means disintegrate), sometimes with formation of loose bodies.[3][4]
Skeletally immature adolescents (whose growth plates have not closed) are more likely to have OCD, which occurs in 15 to 30 people per 100,000 annually.[5] OCD usually causes pain and swelling of the affected joint, catching and locking on movement and a restriction in the range of motion. However, these symptoms characterize many knee conditions and may have many other causes, making OCD relatively hard to diagnose clinically.[6] A diagnosis can be confirmed by X-rays, CT or magnetic resonance imaging (MRI) scans.[7] OCD is classified via diagnostic imaging showing disease progression in stages (I, II, III or IV).[8] After diagnosis the lesion may be treated, depending on its stage, with a form of articular cartilage repair.[9][10]
König[11] coined the term osteochondritis dissecans in 1887, describing it as an inflammation of the bone-cartilage interface.[12] Many other conditions used to be confused with OCD, including osteochondral fracture, osteonecrosis, accessory ossification center, osteochondrosis, and hereditary epiphyseal dysplasia. Some authors have used the terms osteochondrosis dissecans and osteochondral fragments as synonyms for OCD.[13] OCD has been studied in other species of animals; dogs, especially the German Shepherd, are the most commonly affected.[14]
OCD is classified by the progression of the disease in stages. There are two main staging classifications used; one is determined by MRI diagnostic imaging while the other is determined arthroscopically. Regardless of the representation used, this staging represents the pathological conditions associated with the natural progression of osteochondritis dissecans.[15]
While the arthroscopic classification of osteochondral lesions is considered standard, the Anderson MRI staging is the main form of staging used in this article.[8] Stages I and II are stable lesions. Stages III and IV describe unstable lesions in which not only the cartilage is breached, but synovial fluid exists between the fragment and underlying bone.
In osteochondritis dissecans, fragments of cartilage or bone have become loose within a joint, leading to pain and inflammation. These fragments are sometimes referred to as “joint mice”[18] due to a squeaking sound produced by bending the joint. Specifically, OCD is a type of osteochondrosis in which a lesion has formed within the cartilage layer itself, giving rise to secondary inflammation. OCD most commonly affects the knee, though it can also affect other joints such as the ankle or the elbow.[19]
Patients with OCD complain of activity-related pain that develops gradually. Individual complaints usually consist of mechanical symptoms, including pain, swelling, catching, locking, and “giving way”; the primary presenting symptom may be a restriction in the range of movement.[15] Symptoms typically present themselves within the initial weeks of stage I; however, the onset of stage II occurs within months and offers little time for diagnosis. Just as unfortunate is the rapid progression of the disease beyond stage II, as OCD lesions quickly move from stable cysts or fissures to unstable fragments. This progression is compounded when non-specific symptoms (caused by similar injuries such as sprains and strains) lead to a delayed definitive diagnosis.[6]
Physical examination typically reveals an effusion, tenderness, and crepitus. The tenderness may diffuse initially, but often changes to a well-defined focal point as the lesion progresses. Just as OCD shares symptoms with common maladies, acute osteochondral fracture has a similar presentation of tenderness in the affected joint, but is usually associated with a fatty hemarthrosis. Although there is no significant pathologic gait or characteristic alignment abnormality associated with OCD, the patient may walk with the involved leg externally rotated in an attempt to avoid tibial spine impingement on the lateral aspect of the medial condyle of the femur.[13]
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