Importance Ankle sprains are the most common sports-related injuries for which effective preventive measures exist. This review summarises the preventive effectiveness of this neuromuscular training (NMT), culminating in an overview of effective exercise components.
Objective To assess the preventive effect of NMT for first-time and recurrent ankle sprains in sports.
Evidence review An electronic literature search of PubMed, SPORTDiscus and EMBASE was conducted (until 24 March 2016) to identify published randomised controlled trials (RCTs), controlled trials (CTs) and time trend analyses related to NMT as a preventive measure for ankle sprains. Methodological quality of relevant studies was assessed using a predefined set of 19 criteria. Meta-analyses were performed on comparable populations and intervention content.
Findings A total of 30 studies met the inclusion criteria and were analysed (24 RCTs, 3 CTs and 3 time interventions). Studies showed a great diversity in preventive effects and methodological quality (quality score ranged between 47% and 100%). The diversity in preventive effect was independent of study quality and design. A total of 14 studies focussed solely on the effectiveness of balance training, and 16 studies evaluated the effect of balance training combined with adjunct interventions. Pooled data showed a significant reduction in the occurrence of ankle sprains (relative risk (RR) 0.60; 95% CI 0.51 to 0.71). Single-component interventions specifically targeted at ankle sprains achieved preventive effects (RR=0.58; 95% CI 0.48 to 0.72) as opposed to multicomponent interventions (RR 0.67; 95% CI 0.37 to 1.24). With respect to interventions targeted at general injuries, significant effects were found using both single-component (RR=0.71; 95% CI 0.52 to 0.97) and multicomponent interventions (RR=0.55; 95% CI 0.41 to 0.74). Pooled data showed a significant reduction of NMT on ankle sprains in studies including participants regardless of their injury history (RR=0.59; 95% CI 0.49 to 0.71), and in athletes with a previous ankle sprain (RR=0.69; 95% CI 0.49 to 0.98).
Conclusions and relevance NMT is effective at reducing ankle sprains in a sporting population, and in athletes with a previous ankle sprain. The evidence for an effect on first-time ankle sprains remains inconclusive. A key element of NMT to prevent ankle sprains is balance training, irrespective of the use of balance boards or other balance devices. Since both single-component and multicomponent NMT interventions are effective at reducing ankle sprains, the type most fitting to the context should be chosen for implementation efforts.
Level of evidence Level 1.
What is already known?
Ankle sprains are the most common sports-related injury across various sports.
Neuromuscular training (NMT) has been shown in various studies to reduce the risk of recurrent ankle sprains.
What are the new findings?
Preventive effects of NMT are found independent of study design and study quality.
Only NMT intervention programmes that include balance training show a preventive effect on ankle sprains.
Both single-component as well as multiple-component NMT interventions show a preventive effect on ankle sprains.
Ankle sprains are among the most common injuries in sports,1 with a high risk of reinjury during the subsequent 12–24 months.2 ,3 This reinjury can result in chronic pain or instability in 20–50% of all cases,2 ,4 high costs related to healthcare and absenteeism from work,5 and decreased participation in sport and physical activity. As such, prevention of ankle sprains is relevant, both from the perspective of the individual athlete as well as from that of the society as a whole.
Various preventive measures and programmes have been introduced to prevent first-time ankle sprains (ie, primary prevention), recurrent ankle sprains (ie, secondary prevention) or both.6 ,7 These interventions include the use of external supports (ankle brace, tape, bandages), modified footwear and orthotics, neuromuscular training (NMT) and other exercise programmes, or a combination of these. NMT is also referred to as balance training or proprioceptive training, and often includes exercises using ankle disks, balance or wobble boards.7 Current evidence indicates that both external ankle supports (tape and braces)8 ,9 and NMT (balance, proprioceptive training) programmes7 ,10 are effective in preventing recurrent ankle sprains, with an approximated 50% reduction in ankle sprain recurrence risk.6
The majority of studies on the preventive effects of interventions for ankle sprains have reported on NMT programmes.6 These studies evaluated the effect of NMT on various sports, using multiple study designs, and focused on the effect of NMT as a single intervention or as part of a multicomponent intervention.6 ,7 ,10 Additional components included strengthening, agility, plyometrics, education or a combination of several components. Large differences were found between studies in effect size, and a number of studies did not find any preventive effect.6 ,7 However, a recent meta-analysis revealed a statistically significant reduction in ankle sprains favouring NMT as a single intervention (ie, without any adjunct intervention) compared with the control intervention.7 Current evidence also indicates that NMT is an effective secondary preventive measure, while no significant effect has been found for NMT as a primary preventive measure.6 ,7
Where evidence from high-quality studies is necessary to identify effective preventive measures, additional information is necessary to translate and transfer this knowledge into usable intervention messages and strategies for on-field prevention. This is especially true as large-scale implementation of effective preventive interventions in real-world sports settings continues to pose a major challenge.11 Verhagen12 proposed an approach to bridge the gap between the current wide base of knowledge on effective preventive measures and actual injury prevention in daily practice. In particular, increased insight is essential in the working mechanisms of effective preventive measures, effective and appropriate components of preventive programmes, and contexts in which interventions have shown to be effective.12 Relevant contexts to be considered include the target population (age, gender, sports) and intervention approach (eg, supervised or unsupervised, primary or secondary prevention).
As such, it is worthwhile for implementation efforts to compare studies on the preventive effect of NMT with respect to the intervention components and intervention contexts. Since NMT can be evaluated in the general sport population, or in athletes considered to be vulnerable to ankle sprains (ie, selective prevention), it has been recommended to compare these approaches in terms of effectiveness as well.13
Therefore, the aim of this review was to identify relevant information for the implementation of NMT as a preventive measure for first-time and recurrent ankle sprains in sports, based on available intervention studies on this topic. Relevant information includes effective and appropriate intervention components and contexts. Specific objectives of this review were (1) to provide an overview of studies on the effectiveness of NMT to prevent first-time and recurrent ankle sprains among athletes; (2) to assess differences in effectiveness of NMT between single-component and multicomponent interventions (intervention content); (3) to assess differences in effectiveness of NMT between various target populations (intervention context); and (4) to assess differences in effectiveness of NMT between first-time ankle sprains and recurrent ankle sprains.
For the purpose of this review, NMT was defined as an exercise programme or training aimed at improving balance and proprioceptive function at the ankle joint. This is done by re-establishing and strengthening the protective reflexes of the ankle12 and/or challenging the detection and maintenance of ankle joint position.7 We considered all interventions as part of NMT that referred to balance training, exercises using balance boards (also referred to as wobble boards, ankle disks, stability or ankle pads, semi globes), or proprioceptive or NMT as these terms often refer to comparable prevention programmes.7
A search strategy was used to identify all published intervention studies related to NMT as a preventive measure for ankle sprains. Studies on this topic were identified using a computerised literature search (until 24 March 2016) in PubMed, sportdiscus and EMBASE. Database-specific thesaurus terms and free-text terms were used for the keywords ankle sprain and prevention, in combination with (neuromuscular or proprioceptive or balance) training, brace, tape and shoe, respectively. Since terminology for neuromuscular, proprioceptive and balance training is often used interchangeably,7 we searched for all terms. Search terms for brace, tape and shoe were included to retrieve all studies focusing on NMT as a component of a multi-intervention programme. Available filters were used to limit the search to human participants and studies published in the English language. No publication date restrictions were used. Reference lists of systematic reviews were screened for additional relevant studies.
A study was included if (1) the study contained research questions regarding the effectiveness of NMT to prevent first-time and recurrent ankle sprains; (2) the study was a randomised controlled trial (RCT), a controlled trial (CT) or a time intervention (ie, a pretest–post-test design with the preinterrupted data serving as control condition); (3) the results of the study contained a quantitative measure of ankle sprains as the study outcome (eg, incidence rates); and (4) the article concerned original research, published in peer-reviewed English journals. Studies that only reported ankle injuries were included as well, as the majority of ankle injuries in sports are known to concern ankle sprains with high rates in numerous sports.1 Studies involving the rehabilitative treatment of ankle sprains were only included if the interventions under study were intended to reduce the risk of reinjury. Studies aimed primarily at treatment and not at the prevention of ankle sprain recurrences were excluded from this review.
Methodological quality assessment
Methodological quality of all relevant studies was independently scored by two reviewers (IV and EALMV) using the same quality assessment tool that has been applied in two previous reviews on ankle sprain prevention.6 ,14 In order to consider all possible sources of bias, and to introduce more variability in the methodological quality score (QS), five additional criteria were defined following the Cochrane Collaboration's ‘Risk of bias’ tool.15 These criteria were used to assess random sequence generation and allocation concealment (selection bias), blinding of outcome assessment (detection bias), incomplete outcome data (attrition bias) and selective reporting (reporting bias). We omitted the criteria related to performance bias (blinding of participants and personnel) as this was not considered distinctive between the included studies. As such, a set of 19 criteria was used to score the methodological quality (table 1).
Each item of a selected study that met a criterion was assigned a score of ‘1’. If an item did not meet a criterion, was unclear or was not described, a score of ‘0’ was assigned. The highest attainable score was ‘19’. However, not all criteria could be assessed for non-RCTs. These criteria were excluded for these studies. The maximal attainable total score was adjusted accordingly, ie, ‘16’ for CTs (ie, excluding criterion B), and ‘13’ for time interventions (ie, excluding criteria B, C, F and H). In case of disagreement on QS, both reviewers discussed these differences and tried to reach consensus. We used an arbitrary cut-off score of 60%, which has been used in previous reviews on ankle sprain prevention, and considered an adequate way to distinguish between ‘high-quality’ and ‘low-quality’ studies.6 ,14
One reviewer (IV) extracted data describing study design, study participants (number, age, gender), intervention content, intervention context, follow-up period and main outcome measures. For the purpose of this study, intervention content was defined (1) by its components: balance, strength, plyometrics, agility, flexibility exercises, education or a combination; (2) as supervised or unsupervised (eg, by trainer, coach or physiotherapist) and (3) using sport-specific or generic exercises. Intervention context was defined by (1) the target population: general sport population, athletes with and without previous ankle sprain or reduced ankle function; (2) injury scope: ankle sprain, lower extremity (LE) injury or any injury and (3) type of sports. To assess the preventive effects of NMT programmes, unadjusted relative risks (RR) with 95% CIs were extracted. If these measures were not provided, they were calculated on the basis of the ankle sprain incidence data reported. Where appropriate, study results of comparable populations and interventions were pooled using a random-effect model. In order to reduce heterogeneity through risk of bias in pooled effect estimates, only ‘high-quality’ studies were included in the meta-analyses.15 Statistical heterogeneity was assessed using the χ2 test for heterogeneity (p<0.1) and the I2 statistic.15
A total of 838 studies were found, of which 61 full-text articles were screened (figure 1). Twenty-one studies were excluded as the intervention under study did not include NMT.16–36 Another 10 studies were excluded because they compared multiple interventions without a control condition,37–40 did not contain a quantitative measure of ankle sprains or ankle injuries as study outcome,41 ,42 involved treatment of ankle sprains,43 did not assess an intervention effect,44 or concerned a conference abstract45 or commentary.46 This resulted in a total of 30 relevant studies: 24 RCTs,47–70 3 CTs,71–73 and 3 time interventions (prospective cohort studies).74–76 One relevant study was not included in the analyses as no RR could be calculated on the basis of the ankle sprain incidence data reported.75
Since the method of establishing methodological quality for the original 14 criteria did not differ from that in a previous review,6 the quality of corresponding studies was not reassessed for those criteria. The QS of the studies ranged between 47% and 100% (table 2). Five studies were considered to be of low quality,51 ,52 ,65 ,70 ,76 and were excluded from the meta-analyses.
The relevant studies showed a great diversity in the RR of ankle sprain and methodological quality. The diversity in preventive effect was independent of study quality and design (figure 2).
Target population and study outcome
The intervention in four studies was solely targeted at athletes with a previous ankle sprain;51 ,53 ,57 ,65 another three studies involved the rehabilitative treatment of current ankle sprains intended to prevent reinjuries52 ,67 ,70 (table 3). Of all studies, 13 reported on ankle sprains (or ankle injuries) as a primary outcome.47 ,51–53 ,56 ,57 ,65 ,67 ,68 ,70 ,71 ,74 ,76 However, most studies evaluated the effect of NMT on any injury48–50 ,55 ,59 ,60 ,63 ,64 ,66 ,73 or on LE injuries54 ,58 ,61 ,62 ,69 ,72 ,75 including ankle sprains (or ankle injuries) as a secondary outcome.
Effect of NMT by intervention content
All interventions under study included balance training exercises, with 70% using balance boards/devices. A total of 14 studies focused solely on the effectiveness of balance training,47 ,49 ,51–53 ,56 ,57 ,62 ,65 ,68 ,70–72 ,76 whereas the other studies evaluated the effect of a multicomponent intervention. Additional intervention components often included strengthening, plyometrics and agility exercises (table 4).
Pooled data based on the included studies showed a significant reduction in the occurrence of ankle sprains, favouring NMT in interventions that included a form of balance training (RR=0.60; 95% CI 0.51 to 0.71), and in interventions that included balance training using a balance device (RR=0.60; 95% CI 0.50 to 0.72) (table 4). Moreover, NMT interventions including balance training without using balance boards (or other balance devices) also achieved preventive effects (RR=0.60; 95% CI 0.44 to 0.83). This result showed significant heterogeneity (I2=61%; p=0.008).
Effect of NMT by intervention context
Pooled data revealed a significant reduction in the occurrence of ankle sprains using single-component interventions targeted at ankle sprains (RR=0.58; 95% CI 0.48 to 0.72; figure 3). No significant effect was found for multicomponent interventions (RR=0.67; 95% CI 0.37 to 1.24; figure 3). With respect to interventions targeted at LE or general injuries, pooled data revealed significant effects on the occurrence of ankle sprains using both single-component (RR=0.71; 95% CI 0.52 to 0.97; figure 4) and multicomponent interventions (RR=0.55; 95% CI 0.41 to 0.74; figure 4).
With respect to the target population of NMT interventions, pooled data showed a significant reduction of NMT on ankle sprains in studies including participants regardless of their injury history (RR=0.59; 95% CI 0.49 to 0.71), and in athletes with a previous ankle sprain (RR=0.69; 95% CI 0.49 to 0.98; table 5). We could only calculate the RR for one study with regard to the prevention of new ankle sprains, and no significant effect was found (RR=0.55; 95% CI 0.28 to 1.08).56
The effect of NMT was evaluated in a variety of sports (table 3). Per sport, the percentage of studies showing a significant reduction in ankle sprains varied from 33% in handball,58 ,69 ,73 40% in soccer,51 ,57 ,59 ,62–66 ,72 ,75 50% in basketball47 ,49 ,55 ,71 to 100% in volleyball.68 ,74 Single studies evaluated the effect of NMT in indoor soccer,50 floorball61 and American football.76
A practically relevant result of this systematic review is that NMT programmes possess a significant preventive effect on ankle sprains in athletes, irrespective of the content and context of the intervention, study design and methodological quality of included studies. The total effect estimate for RR of ankle sprain (NMT vs control) was 0.60 (95% CI 0.51 to 0.71). This preventive effect has been established in the general sport population, and in athletes with a previous ankle sprain. However, the individual studies show a great diversity in preventive effects and methodological quality (figure 2). This diversity in effects can be explained by the variability among studies in content and context of the interventions. Therefore, additional analyses were done by intervention content and context.
Since all interventions included balance training exercises, this component seems a prerequisite for NMT programmes to prevent ankle sprains (irrespective of the use of a balance device) based on the current literature. To further identify key elements of NMT programmes to prevent ankle sprains, we assessed differences in outcomes between single-component (ie, only balance training) and multicomponent interventions (ie, balance training combined with one or more adjunct interventions). A significant preventive effect on ankle sprains was found for single-component programmes. This effect was present in interventions targeting either any (LE) injury or ankle sprains (figures 3 and 4). These results indicate that balance training alone may be sufficient to prevent ankle sprains, and reinforce previous findings on this topic.6 ,7
The preventive effect and key elements of multicomponent interventions remain inconclusive. Only two studies evaluated the effect of multicomponent interventions specifically targeted at ankle sprains.67 ,74 Pooled results based on these two studies should be interpreted with caution. Only 5 of the 13 studies evaluating the effect of multicomponent interventions on ankle sprains as a secondary outcome reported a statistically significant effect. The lack of effect in these individual studies may be due to insufficient power to detect a significant reduction in ankle sprains. However, pooled results reached statistical significance but showed significant heterogeneity. Additional studies are necessary to determine if interventions including adjunct components next to balance training possess greater preventive value compared with balance training alone. This information can be used to optimise interventions with respect to effectiveness, attractiveness and usability in daily practice (eg, require less time and effort).58 ,77 As such, this may increase the adoption and level of compliance of the intervention, and actual prevention of ankle sprains.78
Subgroup analyses revealed that NMT programmes are effective in reducing the risk of recurrent ankle sprains (table 5). A significant preventive effect was found also when considering athletes regardless of their history of ankle sprains (ie, the entire general sport population). Since only one study presented results considering athletes without a previous injury, no conclusion could be drawn on the primary effect of NMT on ankle sprains. These results underline the effect of NMT as a secondary preventive measure found in previous reviews6 ,14 and meta-analysis.7 However, another meta-analysis on this topic did not find a significant secondary preventive effect.79 The latter meta-analysis included only two studies, of which one was a ‘lower quality’ study. Preventive NMT programmes are often part of the warm-up or training of a sports team, not differentiating between athletes with or without a previous injury. Future studies should assess whether different exercises or intervention components are needed for both groups.
Other intervention aspects should also be considered for the evaluation and implementation of NMT as a preventive measure for ankle sprains. These include the type of sports, supervision, and sport-specific or generic exercises. The integration of sport-specific exercises within a prevention programme may increase its attractiveness, usability and effectiveness as lower-extremity coordination was found to be influenced by movements of the upper body.73 Related to these aspects, both significant and non-significant results were found in the included studies. Meta-analyses were not performed as studies were clinically too heterogeneous when all these aspects were taken into account.15
The preventive effect of NMT is most often evaluated in soccer, basketball, handball and volleyball. This choice is justified as ankle sprains are very common injuries in these sports.1 However, it is recommended that the preventive effect of NMT is also evaluated in other sports at risk for ankle sprains (eg, field hockey, rugby, netball and tennis).
Our review had some strengths and limitations. In contrast to previous reviews on this topic,6 ,7 ,14 we used an extended list of 19 criteria to assess methodological quality of all included studies. More variability in the QS was introduced using this list. Unlike other reviews, evidence based on RCTs, CTs and pretest–post-test designs were combined representing different evidence levels. This can be considered a strength, as we provided an overview of all relevant prospective studies. However, this also resulted in higher methodological heterogeneity among the included studies, and results of the presented meta-analyses must be interpreted with caution. A visual overview was provided of studies on the effect of NMT in preventing ankle sprains, taking the methodological study quality and study design into account (figure 2). This overview was used to identify differences in outcomes between various study designs and methodological QS. Another strength is the use of meta-analyses to assess pooled estimates of the preventive effect of NMT in ankle sprains. ‘Low-quality’ studies14 were excluded from the meta-analyses to reduce heterogeneity through risk of bias and increase validity of results.15 In order to compare study effects, we calculated the unadjusted RR of individual studies on the basis of data provided. This resulted in different outcomes with respect to the intervention effect in seven studies compared with the adjusted outcomes provided.49 ,50 ,54 ,59 ,70 ,71 ,73 Almost all studies in this review included active sport participants. One study included participants active in military training that consisted of various sports and physical activities. Another study did not specify the study population with regard to sports,67 but was included since the results were considered valid for athletes as well. We did not consider the level of compliance to the interventions in our review. However, this is relevant additional information as compliance rates affect study outcomes,80 and have implications for implementation efforts.78
This review provides evidence for the effect of NMT in preventing ankle sprains, taking aspects into account related to both intervention content and context. NMT is effective at reducing ankle sprains in a sporting population, and in athletes with a previous ankle sprain. The evidence for an effect on first-time ankle sprains remains inconclusive. A key element of NMT in preventing ankle sprains is balance training, irrespective of the use of balance boards. Since both single-component and multicomponent interventions are effective at reducing ankle sprains, the type most fitting to the context should be chosen for implementation efforts. As such, this review holds practical value for implementation efforts and for the future development of NMT interventions aimed at preventing ankle sprains in sports.
Competing interests None declared.
Provenance and peer review Commissioned; externally peer reviewed.