Validation of Smartphone-Based Ankle-Control Assessment for Subjects With Chronic Ankle Instability

Ankle sprains can damage ankle proprioception, causing a decrease in postural-control ability; poor postural-control ability is a risk factor in ankle sprain, which creates a vicious circle of recurrent sprains. Proper and early assessment is the key to break down this circle. With smartphones built-in sensors, utilizing smartphones as assessment tools can provide quantitative data of postural-control performance. This study aims to verify the feasibility and validity of smartphone-based ankle-control measurement for subjects with chronic ankle instability (CAI). Twelve participants were recruited. The data of ankle-control performance were simultaneously recorded using a smartphone built-in accelerometer (SBA) and a standalone pre-calibrated three-axial accelerometer (SPA) during a single-leg stance. The smartphone was fixed at the middle of the shin. The participants completed trials under eyes-opened (EO) and eyes-closed (EC) conditions. Each ankle was classified into healthy or unstable ankle using the Cumberland Ankle Instability Tool with 24 as the cutoff score. The average in variation of the three axial acceleration resultant was calculated as the performance index. Pearson's correlation coefficient (PCC) and independent-t test were used to analyze the data, and the statistical significance was set at α = .05. The PCC between SBA and SPA were .960 (p ＜ .001) under the EO condition and .997 (p ＜ .001) under the EC condition. The distinction between the healthy and unstable ankles was also verified. Significant differences existed between the healthy and unstable ankles and also between the eyes opened condition and eyes closed condition as measured by both accelerometers. The results show that utilizing SBA to measure the ankle-control performance exhibited a similar differentiation as that using SPA in evaluating the performance of a single-leg stance test for subjects with CAI.