Evaluation of Chronic Lateral Ankle Instability with a Sprain Stimulator: A Controlled Study in Physically Active Subjects

Abstract

Category: Ankle; Basic Sciences/Biologics Introduction/Purpose: Chronic Lateral Ankle Instability (CLAI) represents a significant socioeconomic burden. Paradoxically, its management has changed little over the years, notably because research is divided into functional and mechanical instability, whereas CLAI encompasses both. Sprain simulators can encompass both functional and mechanical instability by assessing the maximal ankle inversion velocity (MIV) during a simulated inversion trauma. We built a sprain simulator capable of producing a sudden ankle inversion motion during walking. We aimed to differentiate subjects with chronic lateral ankle instability (CLAI) from controls and quantify functional CLAI as well as impairments in activities of daily living and sports using a sprain simulator. Methods: Forty-five physically active subjects were included and assigned to a CLAI group, a control group, or excluded according to the International Ankle Consortium selection criteria. Each subject walked on a treadmill with instability boots after completing the Identification of Functional Ankle Instability (IdFAI) and the Foot Ankle Ability Measurement (FAAM) questionnaires. A simulated trauma was unexpectedly triggered by the observer. Maximal inversion velocities (MIV) were measured at this very moment using inertial moment units. We normalized these values by the average MIV of the 5 stance phases of the same foot preceding the simulated trauma (Ratio MIV). Normality of data were assessed with the Shapiro-Wilk test. The groups were compared using Student T test for normal and Mann-Whitney U test for nonnormal variables. Multivariate linear regressions were performed to assess the relation between, the IdFAI, the FAAM Activities of Daily Living Subscale, the FAAM Sports Subscale and the explanatory variables. Results: Twenty-six ankles were excluded, 32 composed the CLAI group and 32 the control group. Mean MIV were 213.5+/-54.7°/s and 177+/-64.2°/s (p=0.02), and mean Ratio MIV were 1.22+/-0.13 and 1.08+/-0.08 (p < 0.001) in the CLAI and Control groups respectively. In multivariate analysis, Ratio MIV was associated with higher values of IdFAI (β=42.8 [12.9;72.8],p=0.006), lower values of FAAM Activities of Daily Living Subscale (β=-14.1 [-27.8;-0.5],p=0.04) and lower values of FAAM Sports Subscale (β=-7.2 [-13.7;- 0.6],p=0.03) whereas MIV was not. Conclusion: Inversion velocities caused by a sprain simulator clearly differentiated CLAI from controls in our study. Ratio MIV showed good ability to quantify functional CLAI as well as impairments in activities of daily living and sports. This tool should be used in future studies in an attempt to provide a complete picture of CLAI encompassing its functional and mechanical aspects which may lead to improved LAS and CLAI management.