MRI Identification of the Fibular and Talus Position in Patients with Mechanical Ankle Instability.

Specific anatomic variations of the ankle mortise may be found in people with ankle instability. The purpose was to evaluate the fibular and talus position in subjects with mechanical ankle instability (MAI). In this study, MR images of 54 patients with MAI and 51 patients from the author's institution for reasons unrelated to ankle instability were reviewed. The position of the fibular in relation to the talus (axial malleolar index, AMI) and medial malleolus (intermalleolar index, IMI) were evaluated at the axial plane. Meanwhile, the rotation of the talus was measured and calculated using a new index, the Malleolar Talus Index (MTI), which is measured in relation to the medial malleolar. The results showed that the AMI in the MAI patients increased significantly when compared to that in the control group. However, there was no statistically significant difference in the IMI between instability and control groups. The MTI increased significantly in the MAI patients when compared to that in the control group. The conclusion was that the patients with MAI have more of an internally rotated talus than a variation of fibular position.