All methods were performed in accordance with the relevant guidelines and regulations (for example- Declarations of Helsinki) and this is a prospective cohort study and followed STROBE cohort reporting guidelines[10]. From Sep 2018 to May 2020, CAI patients who met the inclusion criteria were screened for enrollment in the study. A priori power analysis was completed using data from a previous study in which the researchers examined the effects of a similar balance-training program[11]. The study was approved by the IRB Medical Committee of the hospital (IRB00006761-M2019164) and the written content was obtained from all patients.
2.1 Patient enrollment
The inclusion criteria were (i) age from 18 to 40 years, (ii) a history of at least one episode of lateral ankle sprain (at least 3 months prior to study enrolment) that caused inflammatory symptoms and disrupted activity for at least one day, (iii) reports of joint “giving way” and/or recurrent sprain and/or “feelings of instability” (iv) scoring <24 on the Cumberland Ankle Instability Tool (CAIT)[12]; (v)grade III[13] injury of anterior talofibular ligament (ATFL) and/or calcaneofibular ligament (CFL) confirmed by MRI findings, positive anterior drawer test (increased translation of 3 mm compared to the uninjured side or an absolute value of 10 mm of displacement)[14], and positive talar tilt test(10° of absolute talar tilt or 5° difference compared to the contralateral side) by TELOS SD 900 Stress Device (Austin & Associates, inc. USA). Specifically, patients with Beighton score≥4 were enrolled into the GJH group and others were enrolled in the non-GJH group[15]. No patients presented history of neurological impairment or fracture. Patients with combined intra-articular lesions (OCLs, osteophyte, impingement, loose body, etc.), history of surgery, fracture requiring realignment, and/or acute injury to the musculoskeletal structures (bone, joint structure and/or nerve) in either lower limb were excluded.
Upon enrollment, all the patients’ basic information was collected and evaluated, including the gender, age, height, weight, involved side, interval from first episode of ankle sprain or instability to enrollment, episodes of sprain and Beighton score. A flow diagram based on the CONSORT statement shows the inclusion and exclusion of subjects through the entire study (Figure 1). Then, all the participants underwent the 12-week balance training intervention by another researcher. The balance training protocol is shown in the Appendix A. The progressive balance-training program were divided into 24 supervised training sessions, two sessions (60 minutes each session) per week. Pre-intervention data-collection session started within 48 hours before the intervention and follow-up sessions were performed post-training and 3 months post-training since the pre-intervention data-collection session. The postintervention data-collection session occurred within 48 hours after the intervention. Participants were instructed to cease all supervised interventions during the follow-up session. During each data-collection session, we administered the patient-oriented outcomes (Foot and Ankle Ability Measure (FAAM), re-sprain ratio) before evaluating the disease-oriented outcomes (isometric ankle strength, postural control).
2.2 Balance training protocol
As was shown in Appendix A, the balance training protocol was designed based on the widely used protocol from the published papers[16, 17]. The protocol includes single-legged stance, wobble board, resistant band and hop exercises.
2.3 Balance Testing
Star Excursion Balance Test: Star Excursion Balance Test (SEBT) was used as a measure of dynamic balance. The 3 SEBT directions that we measured were anterior, posterolateral, and posteromedial, as identified for CAI patients in previous research[18]. Before the SEBT, participants were instructed on proper reaching technique and were allowed four practice trials in each direction[19]. They performed 3 consecutive test trials in each direction. The order of directions was randomized. Each participant stood barefoot with the great toe at the center of the SEBT grid. While standing on the involved limb, they reached as far as possible with the non-stance limb along the reach direction. Keeping their hands on their hips, participants lightly touched the line with the most distal portion of the reaching foot and returned to a bilateral stance. The distance was measured from the center of the grid to the farthest reach point. An unsuccessful trial was defined as a trial in which participants lifted their hands off their hips, moved or lifted the stance foot, lifted the heel, transferred weight to the reach foot when touching the measuring tape, did not touch the tape, did not return the reach foot to the starting position, lost their balance, or were unable to maintain a unilateral stance during the trial. Unsuccessful trials were discarded and reattempted. The maximum distance (centimeters) for each reach direction was recorded. Reach distances were normalized to limb length, which was measured from the anterior-superior iliac spine to the distal tip of the medial malleolus. To calculate the composite score, we added all maximum reach distances, divided the sum by 3 times the limb length, and multiplied the quotient by 100. This composite score was used for statistical analysis.
Balance Error Scoring System: Balance Error Scoring System (BES) is a measure of static balance and consists of 3 stances: double-legged stance, single-legged stance, and tandem stance in a heel-to-toe fashion[20]. Participants performed all stances on firm and foam surfaces (model Balanced; Airex AG, Sins, Switzerland) with their hands on their hips and eyes closed[20]. They performed one practice trial for each condition to ensure proper technique, followed by one test trial. Total errors were counted for each 20-second trial. An error was defined as lifting the hands off the iliac crests; opening the eyes; stepping, stumbling, or falling; moving the hip into more than 30° of abduction; lifting the forefoot or heel; or remaining out of test position for more than 5 seconds[20]. The maximal possible score for each stance was 10. The total score was used for statistical analysis.
2.4 Isokinetic strength measurement
As described in TW Kaminski’s research[21], isokinetic strength was assessed with a Biodex isokinetic dynamometer (Biodex Medical Systems Inc, Shirley, NY). Each subject’s foot was securely fastened on the chair, with the hip angle 80◦ flexion (0◦ neutral position) and 20°to 30° of knee flexion. Each subject was allowed three submaximal (50% capacity) warm-up repetitions at each velocity to become familiar with the isokinetic test procedure, then performed three maximal concentric test repetitions at 60 and 120°/s on both ankles. The resting interval was approximately one minute between tests for each motion, velocity, and side. At the end of testing, peak torque data was extracted from the torque curves.
2.5 Data analysis
The self-reported function (FAAM and ankle sprain recurrence), balance measures (SEBT test and BES test) and isokinetic muscle strength were analyzed separately at pre-training, post-training, and 6 months. Shapiro-Wilk test was used to assess Normality of data. Two-way repeated measure ANOVA was used to analyze time differences and group differences. Alpha level was set a priori at P < .05. An a priori power analysis was completed using data from a previous study[17] in which the researchers examined the effects of a similar balance-training program. Based on an α level of .05, a power of .95, and an effect size of .97 determined by the FAAM-Sport, 16 participants were needed. Therefore, we enrolled 20 participants to account for up to 20% attrition. Patients completed at least 21 sessions were included in the analysis and if they did not complete any follow-up measurements, their data would not be taken into analysis.