Is the fibula positioned anteriorly in weight-bearing in individuals with chronic ankle instability? A case control study

Background: Clinically, a discrepancy of fibular position in relation to the tibia has been proposed as a factor in the persistence of chronic ankle instability (CAI). Previous studies have produced conflicting findings, perhaps due to varying radiological methods and measurement of participants in non-weight-bearing positions. Objectives: To compare normalized-fibular position in weight-bearing in individuals with CAI with healthy controls. Design: A weight-bearing lateral X-ray was taken of the affected ankle of 33 adults with CAI and 33 matched controls. The distance between the anterior edges of the distal fibula and tibia was recorded, and then normalized as a proportion of maximal tibial width. Normalized-fibular position was compared between groups using independent t-tests. Intra-class correlation coefficients (ICC(2,1)) were calculated to determine reliability of measurements. A receiver-operating characteristic (ROC) curve was used to determine sensitivity, specificity, and a cutoff score to differentiate individuals with CAI from controls using normalized-fibular position. Results: Normalized fibular position was significantly different (CAI, 29.7 (6.6)%; healthy, 26.7 (4.8)%) between the groups. Measurement of intra-rater (0.99, 95%CI = 0.98 to 1.00) and inter-rater (0.98, 95%CI = 0.96 to 0.99) reliability were both excellent. The threshold normalized-fibular position was 27%, with a score more than 27% indicating a greater chance of being in the CAI group. Sensitivity was 69.7% and specificity was 54.5% for this threshold. Conclusion: A slightly anteriorly positioned fibula in relation to the tibia was observed in people with CAI. Specificity/sensitivity scores for normalized-fibular position indicate that it has little ability to predict CAI alone.