To evaluate the position of the talus and fibula on axial magnetic resonance imaging (MRI) images of patients with chronic ankle instability (CAI).

Fifty patients who were hospitalized in the Department of Orthopedics of Renhe Hospital Affiliated to China Three Gorges University from January 2019 to July 2023 were enrolled as as the experimental group (the included patients were diagnosed with CAI with anterior talofibular ligament injury; patients with a history of previous lower limb joint surgery or deformity were excluded). The other 50 patients who visited this hospital for other diseases were enrolled as control group (excluded those with ankle joint-related bony or ligamentous injuries). A retrospective analysis was performed on the data of the enrolled patients. The axial malleolar index (AMI), inter malleolar index (IMI), malleolar talus index (MTI), central malleolar index (CMI), and midpoint inter malleolar index (MIMI) were measured using the measurement tools within the Picture Archiving and Communication System (PACS) of the hospital. The distance (d) between the center of the fibula and the axis line of the proximal tibia was measured at the level of the axial image layers near the joint; t test and Wilcoxon rank sum test were applied for statistical analysis.

No statistically significant differences were found in age, gender ratio, affected side ratio, height, weight, or body mass index (BMI) between the experimental group and the control group. There were no significant differences in angular measurements between the two groups ( all P>0.05), the data were as follows: AMI (-10.8±4.8)°vs. (-10.4±5.5)°, IMI (-9.3±3.7)° vs. (-9.4±3.9)°, CMI (-15.8±6.5)° vs. (-13.9±5.8)°, MIMI (-8.4±3.7)° vs. (-8.3±3.6)°, MTI 86.00 (84.00, 88.00)°vs.85.00 (83.00, 87.00)°. The experimental group showed a more posterior position of the fibular center relative to the distal tibial axis compared to the control group (Z=2.562, P<0.05).

In CAI patients, the position of the fibula relative to the tibia is displaced posteriorly on MRI axial images, with no significant change in the position of the talus.