The Effectiveness Sustainability of Supervised Balance Training in Chronic Ankle Instability With Grade Iii Ligament Injury: A One-year Prospective Study

Background: To determine the effectiveness sustainability of the supervised balance training in the chronic ankle instability (CAI) cases with grade III ligament injury. Methods: Twenty young adults (12 males and 8 females) diagnosed as CAI with grade III ligament injury underwent a 3-months supervised balance training. The self-reported functional questionnaire, plantar pressure, and isokinetic ankle strength were consecutively evaluated at pre-training, 3 months, 6 months and one year. Paired T test was used to explore the changes of muscle strength and foot pressure to evaluate the effectiveness sustainability of balance training. According to whether the patient has sprain recurrence, the patients were divided into sprain recurrence group and control group. The risk factors of sprain recurrence were explored with univariate analysis and multivariable logistic regression. Results: The self-reported functional scores, the plantar pressure distribution and the muscle strength showed signicant immediate improvements after 3-month supervised balance training. At post-training 6 months, peak force under 2 nd metatarsal, time to peak force under the medial hindfoot, time to boundary measurements and dorsiexion, and eversion strength were partly declined to the pre-training level. 16 patients (80%) resumed the daily life and sports without sprain recurrence during the follow-up. Four patients (20%) reported ankle sprain during the follow-up, and the sprain recurrence group showed signicantly higher Beighton scores (p=0.012) and weaker initial inversion strength (p=0.022) than the control group. Conclusions: Three months’ supervised balance training could effectively improve postural control and muscle strength of the CAI cases with grade III ankle ligament, although these improvements would be partial deceased over time. Additional strength exercises for dorsiexion and eversion should be supplemented from 6 months. Higher Beighton score and initial inversion muscle strength weakness might increase the risk of sprain recurrence.


Introduction
Lateral ankle sprain is a common musculoskeletal injury in sports 1 . Although most patients resumed daily life after the primary sprain, about 34% of individuals suffered from chronic ankle instability (CAI), which is characterized as recurrent sprain, episodes of giving-way of the ankle joint, pain, de cits of postural control and muscle strength 1 . Treatment strategy includes conservative or operative solutions, mainly depending on the severity of ankle sprains, which are classi ed from grades I to III (mild, moderate or severe) 2 . Conservative treatment is more effective for CAI patients with Grade I and Grade II ligament injuries while treatment for the chronic ankle instability (CAI) with grade III injuries is controversial 3 .
Surgery is commonly recommended to CAI patients, especially to those with combined intra-articular lesions (osteochondral lesions (OCLs), osteophyte, impingement, loose body, etc) causing obstructive symptoms [4][5][6] . However, considering the invasiveness and potential complications of the surgery, conservative treatment could be the rst choice for the CAI cases with isolated lateral ankle ligament but without intra-articular lesions.
Balance-training programs were proven to be effective in improving postural control and muscle strength in CAI patients 7 in short term. However, some research suggested that the effectiveness of conservative treatment (such as subjective symptoms 8 and eversion muscle strength 9 ) might be temporary, and about 21.4% CAI patients still had re-sprains 8 and the postural stability de cits at 6 months post-intervention 9 .
However, previous studies merely targeted some single treatment (such as resistance tubing 8 and wobble board 9 ), and the follow-up period was only 6 months. In addition, those studies included the CAI cases with varying degree of ligament injury but did not distinguish the CAI cases with grade III ligament injury.
By now, there has been few evidences for long-term effectiveness and continuity after systematic rehabilitation training for CAI patients with grade III ligament injury.
In terms of the post-training functional evaluation, most of the studies focused on the subjective feeling instead of objective evaluation, thus, made it di cult to guide the clinical practice. In fact, the foot pressure measures, such as center-of pressure (COP) excursion, time-to-boundary (TTB) and peak plantar analysis have been commonly used to identify the postural control de cits of those with CAI. The CAI cases had signi cantly less time to make postural corrections to meet the stability demands 10 and a signi cantly increased lateral loading 11 compared with healthy controls. These objective parameters might be important predictors for the effectiveness sustainability and help treatment decision making.
In the present study, 20 CAI patients with isolated lateral ankle ligament injury were included and accepted 3-months supervised balance training and consecutive follow-up for 1 year. The purpose of present study was to determine the mid-term effectiveness and the sustainability of balance training program and preliminarily explore the risk factors of sprain recurrence in the CAI cases. We hypothesized that balance training would improve the muscle strength, foot pressure distribution and postural stability, but some improvements would be weakened with time. These results may help us optimize rehabilitation strategies to improve the effectiveness of balance training for the CAI cases with grade III ankle ligament injury.

Design
From Sep 2018 to Apr 2019, 20 CAI patients who were diagnosed as grade III ligament injury and ready for rehabilitation were included 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 12 .
The study was approved by the IRB Medical Committee of our hospital (IRB00006761-M2019164) and the written content was obtained from all patients. The study was registered in Chinese Clinical Trial Registry (ChiCTR), and the number was ChiCTR1900023999.

Patient enrollment
The inclusion criteria were (i) aging from 18 to 40, (ii) a history of at least one signi cant lateral ankle sprain (at least 12 months prior to study enrolment) that caused in ammatory symptoms and disrupted activity, (iii) the most recent ankle sprain occurred >3 months prior to study participation, (iv) reports of the previously injured joint "giving way" and/or recurrent sprain and/or "feelings of instability" (v) scoring <24 on the Cumberland Ankle Instability Tool (CAIT) 13 ; grade III [14][15] injury of anterior talo bular ligament (ATFL) and/or calcaneo bular ligament (CFL) con rmed by both MRI and positive anterior drawer test (increased translation of 3 mm compared to the uninjured side or an absolute value of 10 mm of displacement) 16 and talar tilt test(10° of absolute talar tilt or 5° difference compared to the contralateral side) 17 by TELOS SD 900 Stress Device (Austin & Associates, inc. USA). All patients presented without a history of neurological or orthopedic impairment. Patients with combined intra-articular lesions (OCLs, osteophyte, impingement, loose body, etc), a 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, pre-duration, sprain time and the Beighton score. The Beighton score≥4 was de ned as the generalized joint hypermobility (gJHM). Then all the participants underwent the 3month balance training intervention. The progressive balance-training program divided into 24 supervised training sessions, two sessions (60 minutes each session) per week. The postintervention data-collection session occurred within 48 hours after the intervention ended. A follow-up session was performed 3 months, 6 months and 1 year since the pre-intervention data-collection session. Participants were instructed to cease all interventions during the follow-up session. During each data-collection session, we administered the patient-oriented outcomes (Foot and Ankle Ability Measure (FAAM), Cumberland Ankle Instability Tool (CAIT)) before evaluating the disease-oriented outcomes (isometric ankle strength, foot pressure and static and dynamic postural control). Plantar pressure and posture control evaluation The patients underwent three trials of single-limb stance on each leg with eyes closed on a force plate (AMTI; Watertown, MA, USA) for 10s 10,18 . COP data were calculated from the three-dimensional force and moment signals and sampled at a rate of 50 Hz. 18 Subjects were instructed to stand as still as possible during testing with arms folded across their chests, holding the opposite limb at approximately 45° of knee exion and 30° of hip exion in accordance. If a subject touched down the ground, contacted with the stance limb, or was unable to maintain standing posture during the 10-s trial, the trial was terminated and repeated. TTB measures and COP measures were computed separately in the ML and the AP directions using previously described methods 10,18 .
Subjects walked six times in barefoot over the pressure plate (Footscan, RSscan International, Olen, Belgium) with 120 Hz sampling rate 19 . Three walks for each foot were recorded and printed. Each print consisted of a time peak-force curve for eight regions of interest on the foot. The regions of interest, which were analyzed automatically by the system software, were medial heel (HM), lateral heel (HL), 1st to 5th metatarsal heads(M1~M5), and toes(T1). The time variables were calculated as the ratio of time from the start of the stance to peak force under the region of interest and the total stance time. The peak force variables were calculated as the ratio of the peak force under the region of interest, and were normalized by the body weight 20 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 biodex chair, with the hip angle 80• exion (0• neutral position) and 20°to 30° of knee exion. 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 were extracted from the torque curves.

Balance training protocol
As was shown in table 2, the balance training protocol was designed based on the widely used protocol from the published papers [22][23] . The protocol includes single-legged stance, wobble board, resistant band and hop exercises and so on.

Performed with eyes opened and eyes closed
Progressed when participants could complete a 60-s trial without a loss of balance.
Increased no. of repetitions by 1 Changed surface from oor to using the Dyna-Disc a .

Wobble board
Slowly moved the board in the plantarexion/dorsi exion and inversion/eversion directions without letting the board contact the oor.
Performed up to 10 repetitions in each direction.
Progressed when participant could complete the task without upper extremity support.
Added rotational directions.
Steamboats Tied a 48-in Thera-band around the unstable ankle.
Positioned stance foot 27-in from where Thera-band was tied.
Performed up to 3 sets of 15 repetitions in each direction (hip exion, extension, abduction, adduction).
Progressed when participants could complete the repetitions without a loss of balance or fatigue.
Increased no. of repetitions from 10 to 15.
Progressed to next level of resistance with the Thera-band.

Singlelegged hop
Hopped as far as comfortable in the anterior direction.
Performed up to 15 repetitions.
Progressed when participants could perform the task with minimal ankle and hip motion and no loss of balance on landing.
Increased no. of repetitions from 5 to 10 to 15.
Encouraged increased distance to participants' tolerance.
Progressed to medial, lateral, and posterior directions.

Quadrant hop
Hopped in numbered squares clockwise and counterclockwise while maintaining single-legged stance.
Progressed when participants could complete 2 sets of 5 hops without a loss of balance or fatigue Made unanticipated directional changes where investigator randomly called out numbers.

Singlelegged ball catch
Performed up to 3 sets of 20 tosses Progressed when participants could perform 20 tosses without a loss of balance.
Tossed ball outside participants base of support.
Performed during stance on a DynaDisc.

Toe touch down
Maintained single-legged stance on a step while lowering the unstable ankle in the anterior, posterior, medial, and lateral directions until the foot contacted oor. Based on the ankle sprain recurrence after the balance training program through one year, the patients were divided into the sprain recurrence group and control group. The pre-training variables for each patient was used to analyze the risk factor for the sprain recurrence after the balance training.

Data analysis
The self-reported function (FAAM and CAIT), postural control measures (TTB measures and COP-based measures, plantar pressure measures) were analyzed separately at pre-training, post-training, 6 months and 1 year. Paired sample t test was used to assess changes in the dependent measures before and after balance training. Shapiro-Wilk test was used to assess Normality of data. Univariate analysis and multivariable logistic regression model were used to explore the risk factors of sprain recurrence after the balance training, Alpha level was set a priori at p < 0.05. An a priori power analysis was completed using data from a previous study 24 in which the researchers examined the effects of a similar balance-training program. Based on an α level of .05, a power of 0.95, and an effect size of 0.97 determined by the FAAM-Sport, 16 participants were needed. Therefore, we enrolled 20 participants to account for up to 20% attrition.

Results
Self-reported questionnaire The changes of self-reported function questionnaires are presented in the Figure 1.

Muscle strength
As was shown in Figure 4, all the isokinetic contraction strength was signi cantly improved after 3 months' balance training (p<0.05). Continuously signi cant increase in the 120°/s, 60°/s PF and 120°/s IV strength was observed during the one year follow up (p<0.05), but the dorsi exion and eversion muscle strength decreased to the pretraining level (p>0.05) after six months till one year and the improvements in the partial(60°/s) inversion muscle strength decreased after one year.

Risk factors of sprain recurrence
To preliminarily explore the potential risk factors of recurrence, the univariate analysis and multivariable logistic regression model were used. Based on whether the scores <24 CAIT or there was an obvious ankle sprain during the follow up, the patients were divided into the sprain recurrence group (n=4) and the control group (n=16

Discussion
The most important nding of the present study was that the 3 months of supervised balance training signi cantly improved self-reported function, postural control, and muscle strength for CAI patients with isolated ligament injury. However, some improvements on postural control and muscle strength were declined after 6 months and 1 year. Additional strength exercises for dorsi exion and eversion should be supplemented from 6 months. The generalized joint hypermobility (gJHM) and the initial inversion strength weakness could be the potential risk factors for sprain recurrence after balance training.
According to the results, most of CAI patients with grade III ligament injury had satisfactory outcomes after the balance training. Similar self-reported function questionnaire [25][26] and muscle strength [27][28] improvements were also found in the previous studies, but none of them investigated the long-term effectiveness of balance training and distinguish the severity of the ligament injury. The results of the present study implicated that the balance training is still effective even for patients with severe ligament injuries in the long run. Although the ligaments are completely broken in the acute phase and the joints are obviously loose in the chronic phase, the feeling of instability is partly improved by increasing the muscle strength and the posture control. However, we found that the strength improvement in dorsi exion and eversion disappeared in the 6 months follow-up and a similar situation occurs with 60° eversion muscle strength at 1 year. It could be inferred that balance training will have a short-term muscle strength improvement and additional strength exercises for dorsi exion and eversion from 6 months and inversion exercise from 1 year might enhance and maintain the effect of balance training again. Further studies are needed to improve the balance training program for the CAI cases.
For the plantar pressure evaluation, we found a signi cant change in the TTB related measures during the single leg standing. TTB related measurements was a spatiotemporal analysis of COP data points, which was a novel approach to assessing postural control de cit in single-limb stance 10,29 . It quanti ed the theoretical amount of time an individual had to use to make a postural correction to maintain postural stability. The results indicated that the grade III CAI patients needed longer time to reach the balance boundaries and less risk to fall after the balance training. During the walking, we found that the TPF of HM came more delayed and M2 came earlier after the balance training, which means a shorter duration of contact of the heel to central forefoot. The longer duration indicated a slowing down of weight transfer from heel strike to toe off, which was a sign of walking stability improvement 20 . The results also showed that greater loading under the M2 and HM which indicates a medial shift of the center of pressure so as to decrease the susceptibility of ankle sprain 11 . However, improvements on stability during single leg standing and pressure distribution during walking was declined gradually over time.
The present study showed that the sprain recurrence patients had signi cant higher Beighton scores, which indicated that the patients with gJHM might have poor rehabilitation effect for balance training.
Some previous studies [30][31] reported generalized joint hypermobility was an intrinsic risk factors related to recurrent lateral ankle sprain, so the hypermobility of ankle joint structure might increase the risk of ankle injury during the rehabilitation process. Similar poor outcomes were also found in the clinical surgery treatment, such as the modi ed Broström procedure 16, 32 . In those cases, the repaired ligaments would eventually stretch out and the patients need a longer period for lateral ligament recovery. However, the impact of gJHM on conservative treatment effect was rarely reported. In theory, the increased muscle strength brought by functional training can enhance joint stability. However, the joint capsule of these patients with gJHM may be also with excessive relaxation, so that the improvement of muscle strength is not enough to restore su cient stability. This may be the reason for the relatively poor results of these patients. Considering the limited number of cases, the effect and the mechanism of joint hyper-relaxation on conservative training requires further controlled studies.
In this study, we also found the relatively weaker 60°/s inversion strength could be another risk factor of the failure. Several studies have shown that subjects with CAI exhibited strength de cits in their invertor musculature [33][34][35] . It is suggested that the ankle joint invertors play an integral role in controlling the rate of calcaneal eversion as the body's center of mass is displaced laterally beyond the base of support 36 .
The weakness in inversion strength lead in uncontrolled weight transfer to the lateral side of the foot during balance training, thus increased frequency of ankle inversion episodes. For the patients with inversion strength weakness, more speci c and targeted rehabilitation needed to be done.
To our knowledge, this is the rst comprehensive study to investigate the long-term effectiveness and its related factors of sprain occurrence for the CAI patients with isolated grades III ligament injury. The strength of this study included a relatively long-term follow-up, a detailed systematic balance training protocol and a comprehensive evaluation of the patients and the objective assessment on the postural control improvement in terms of plantar pressure and TTB. It was important to note that although some improvements seem not to last over time, the rehabilitation for the severe type of CAI patients were still effective in the long term. Our results provided more evidence for the use of balance training in CAI cases and would help to optimize the rehabilitation plan. Those with high-risk factors might be prompted to receive more aggressive treatment early, including surgery.
There were still some limitations of the present study. Firstly, the sample size was relatively small in the sprain recurrence group although overall participants enrolled in this study was calculated by the sample size, larger sample are needed to be included in the future research. Secondly, this study was included merely lateral ligament injury while other ligament and syndesmosis injuries also impeded rehabilitation outcomes. So, our results were only suitable for the isolated lateral ankle ligament injury, the balance training for more complex injury type are needed in the future.

Conclusion
For the grade III CAI patients with isolated lateral ankle ligament injury, the 3 months' supervised balance training program signi cantly improved FAAM scores, foot pressure distribution, static postural control and muscle strength. However, the effectiveness may be partial declined after 6 months and 1 year.
Additional strength exercises for dorsi exion and eversion should be supplemented from 6 months. The high Beighton score and the initial inversion muscle strength weakness might be the potential risk factors of sprain recurrence after balance training. Availability of data and materials The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.   Foot pressure distribution changes of the patient from respective control group(a~d) and sprain recurrence group(e~h) in three-dimension model (Screenshot from footscan 7.0 software). The gures showed the peak force during the walking at pretraining, 3, 6 and 12months post training. After the balance training, the foot distribution in the control group turned to the medial side of foot(a~d) while the foot distribution in the sprain recurrence group turned to the medial side then reversed to lateral side of foot again (e~h).