[Analysis of bilateral changes in static postural stability and visual dependence characteristics in individuals with...

Objective: To assess the bilateral differences in static postural stability among patients with chronic ankle instability(CAI) using inertial sensors, and to further analyze their dependence on visual input. Methods: The CAI patients prospectively enrolled from the Sports Medicine Department outpatient clinic of Peking University Third Hospital between May 2024 and December 2024 as the CAI group, and concurrently enrolled healthy people from society as the healthy control group. An inertial sensor was firmly affixed to the lumbar region (L₃-L₅) of each participant. Under both eyes-open and eyes-closed conditions, participants performed three single-leg standing trials on each leg while data were simultaneously collected from a force plate and the inertial sensor. Static postural stability was assessed using two primary indicators: the root mean square of acceleration (RMS_acc), calculated from the resultant acceleration derived from tri-axial accelerometer signals; and the mean velocity of the center of pressure (COP_MV), derived from the anterior-posterior and medial-lateral displacement velocities of the center of pressure measured by the force plate. Differences in RMS_acc and COP_MV between the two groups under different conditions were compared, and the intraclass correlation coefficient (ICC) was calculated to assess agreement between the inertial sensor and force plate measurements. Results: A total of 56 participants were included, 28 in the CAI group and 28 in the healthy control group. The CAI group included 14 males and 14 females with a mean age of (28.5±6.1) years, while the healthy control group included 10 males and 18 females, aged (27.5±6.4) years; there was no significant differences between the two groups in terms of gender or age (both P>0.05). The CAI group had significantly lower CAIT score than the healthy controls [(15.2±3.0) vs (29.2±1.5) points, P<0.001] and reported a greater number of previous ankle sprains [(4.2±1.3) times vs 0 time, P<0.001]. Under eyes-open conditions, the affected side of the CAI group exhibited higher RMS_acc [M(Q₁, Q₃)][0.81 (0.68, 1.38) m/s²] and COP_MV [(2.45±0.36) mm/s] than the non-dominant limb of the healthy controls [0.31 (0.22, 0.41) m/s², 1.69 (1.54, 2.25) mm/s, respectively] (both P<0.05). Under eyes-closed conditions, both the affected [RMS_acc: 0.95 (0.62, 1.11) m/s²; COP_MV: (6.20±1.72) mm/s] and unaffected sides [RMS_acc: 0.51 (0.37, 1.03) m/s²; COP_MV: 4.17 (4.05, 5.36) mm/s] of the CAI group were significantly higher than those of the corresponding sides of the healthy controls [(0.38±0.28) m/s² and (3.74±1.61) mm/s, respectively] (all P<0.05). Consistency analysis between RMS_acc and COP_MV showed moderate agreement in the CAI group across different visual conditions and stance sides (ICC=0.51-0.72), whereas the healthy control group displayed lower and more variable consistency (ICC=0.39-0.65). Conclusions: Lumbar-mounted inertial sensors can objectively capture postural instability during single-leg stance in individuals with CAI. Participants with unilateral CAI exhibited impaired postural stability both on the affected and the unaffected side, and show an increased dependence on visual input.