Osteochondritis Dissecans

Osteochondritis dissecans (OCD) is an osteochondral stress injury usually seen in older children and adolescents. It can also be seen in adults, either as a de novo process (less common), or as progression of previously asymptomatic juvenile OCD. Juvenile OCD has a better prognosis and higher response rate to conservative therapy than its adult form.

OCD is characteristically seen at the lateral aspect of the medial femoral condyle. In the knee, OCD can also be seen in the lateral femoral condyle, femoral trochlea, and the patella. OCD can also be seen at the distal capitulum, humeral head, and medial talar dome.

The lesion begins as a sunchondral stress reaction (edema on MRI) with intact overlying cartilage. Enhancement at this stage implies an intact blood supply.

The process may progress, leading to a fracture plane parallel to the cortex, but with a still-intact overlying cartilage.

The fracture plane may completely separate the fracture fragment from the bone and interrupt its blood supply. The fragment may be kept in place, however, by the overlying cartilage, which may still be partially intact.

The next stage is progression to an in situ loose body with complete disruption of the overlying cartilage, and finally progression to an intra-artiular loose body.

Prognosis and MRI

Prognosis has been found to depend on stability of the lesion and MRI can be used to detect unstable lesions. Different MRI criteria have been suggested for adult and juvenile OCD in the knee. The location and size of lesions were not found to be correlated with stability.

Signs of instability in an adult OCD lesion (100% sensitive and 100% specific) are a T2-hyperintense rim or cysts surrounding an OCD lesion.

In juvenile OCD a T2-hyperintense rim was found to be specific for OCD instability only if the rim demonstrated fluid signal intensity, was surrounded by a second outer rim of low T2 signal intensity, or was accompanied by multiple breaks in the subchondral bone plate. In addition, cysts surrounding a juvenile OCD lesion were found to be specific for instability only if they were multiple or larger than 5 mm in size.

References

• Kijowski R, Blankenbaker DG, Shinki K, Fine JP, Graf BK, De Smet AA. Juvenile versus adult osteochondritis dissecans of the knee: appropriate MR imaging criteria for instability. Radiology. Aug 2008;248(2):571-8.
• Musculoskeletal Radiology: The Requisites. Third edition. Chapter 13, pages 234-237.