Effect of a Semi-rigid Ankle Brace on the In Vivo Kinematics and Muscle Activity of Patients with Functional Ankle Instability During Simulated Ankle Sprain

Background: Ankle braces can effectively decrease the incidence of recurrent ankle sprain; however, whether the brace can decrease the severity of sprain and its related mechanism during sprain remain unknown. Methods 22 patients with functional ankle instability (FAI) (12 males and 10 females) and 16 healthy subjects (8 males and 8 females) were enrlled in this study. All of the subjects walked on a custom-built tilting platform that offered a 30° inversion to mimic the inversion of ankle sprain. We collected the kinematic and sEMG data of patients with FAI with or without ankle brace and normal controls six times. Results The FAI without brace group showed significantly higher maximum inversion angles and average inversion velocities than the control group (P < 0.001). The FAI with brace group revealed significantly lower maximum inversion angles and average inversion velocities than the FAI without brace group (P < 0.001); this group also showed significantly higher maximum external rotation angle and average external rotation velocities than the FAI with brace (P < 0.001) and control (P < 0.001) groups. The FAI with brace group indicated significantly lower average EMG Prep (P = 0.047), EMG Tilt (P = 0.037), and EMG afterTilt (P = 0.004) of the peroneus longus (PL) than the FAI without brace group. Conclusions The ankle brace could effectively decrease inversion angles and their velocities and increase external rotation angles and their corresponding velocities during ankle sprain in patients with FAI. It could also decrease the activity of the PL muscle during ankle sprain.