Discrimination Between Mechanical and Functional Ankle Instability, and Copers: A Questionnaire-Based Analysis

This study aimed to differentiate subgroups of chronic ankle instability (CAI), including mechanical ankle instability (structural damage), functional ankle instability (FAI: neuromuscular deficits), Copers (individuals who recovered functional stability without recurrent symptoms), and controls (healthy individuals), using a validated questionnaire set (Cumberland ankle instability tool [CAIT], identification of functional ankle instability [IdFAI], ankle instability instrument [AII], foot and ankle ability measurement [FAAM]/Activities of Daily Living, FAAM/Sports). Additionally, we sought to present a standardized scoring system to classify CAI, Copers, and control participants.

Case-control study.

A total of 104 people participated in the study, including 26 mechanical ankle instability, 26 functional ankle instability, 26 Copers, and 26 healthy controls. The Kruskal-Wallis test was used for analysis, and the Mann-Whitney test was used for post hoc tests. The cutoff value for each group was confirmed using the receiver operating characteristic curve.

Analyses comparing the CAI, Copers, and control groups revealed significant differences in CAIT (P < .001), IdFAI (P < .001), AII (P < .001), FAAM/Activities of Daily Living (P < .001), and FAAM/Sports (P < .001). The cutoff values for each group were confirmed for CAIT, IdFAI, AII, FAAM/Activities of Daily Living, and FAAM/Sports. For CAIT, it was 0 to 8.5 mechanical ankle instability, 8.6 to 23 for functional ankle instability, 24 to 29.5 for Copers, and 29.6 to 30 for control.

These findings support using CAIT, IdFAI, and AII to classify CAI subtypes and identify Copers. Questionnaire-based cutoff values may assist rehabilitation planning and clinical decision-making. A CAIT score below 8.5 may indicate surgical consideration, supported by comprehensive clinical assessment.