Undisplaced lateral(stage 3) lesion. Lateral lesions are more often visible on plain films
Occasionally other diagnoses such as inflammatory arthritis will be suggested by the clinical picture and require appropriate investigation. However, imaging is the main investigation.
Plain films will show about half of all lesions and will also show other fractures, spurs and joint narrowing. Our radiology colleagues prefer to obtain plain radiographs before MR.
Isotope bone scanning will show an area of increased activity at the site of an OCD, but has been largely superseded by MR and CT.
CT showing a small medial cystic lesion
CT shows bony fragments and cysts well, but does not show bone oedema or cartilage defects. CT arthrography, however, shows cartilage lesions at least as well as MR arthrography (Schmid et al 2003), and helical CT performed as well as MR in the study of Verhagen (2005)
MR is probably the imaging modality of choice, showing cartilage and bone lesions well, including bone oedema. The significance of oedema is not yet clear; it can be seen even after normal exercise and does not always reflect clinical problems or prognosis. Robinson et al (2003) recommended MR in any ankle injury which is failing to settle after 3 months, and we generally follow this.
T1-weighted MRI - impaction (B+H stage 1/Bristol stage 2) lesion
T2-weighted MRI - large cystic (Bristol stage 5) lesion