Electrotherapy as a Rehabilitation Modality for Chronic Ankle Instability: A Systematic Review

Objectives

In the present study, we systematically review studies in which electrotherapies were used in combination with TEx to improve functional outcome measures in those with CAI.

Study Design

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) in Exercise, Rehabilitation, Sport medicine and SporTs science (PERSiST) guidelines (Figure) were followed when conducting this systematic review, accompanied by the PRISMA literature search extension (PRISMA-S).^37–39 The protocol of this systematic review was prospectively registered on PROSPERO (CRD42022328704).

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Eligibility Criteria

Eligibility criteria were formulated using the Population, Intervention, Comparison, Outcome, and Study Design (PICOS) method (Table 1).⁴⁰ These were as follows: population: human participants without restriction on sex, age, or setting; interventions: electrotherapy in any form as part of rehabilitation for CAI in combination with TEx; comparison: TEx for rehabilitation only; outcome: the effectiveness of electrotherapy combined with TEx in functional outcome measures such as, but not limited to, balance, muscle strength, patient self-reported outcomes, muscle latency, and postural stability; study design: randomized controlled trials. All studies included were full-text articles published in English and peer-reviewed journals. All electrotherapy types were included to rehabilitate CAI when combined with TEx. Electrotherapy applications for acute ankle sprains or treatment of CAI without the inclusion of TEx were excluded.

Table 1.PICOS Method Used to Formulate Eligibility Criteria

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Search Strategy

One reviewer independently searched PubMed, MEDLINE, SPORTDiscus, and Web of Science databases from inception to September 16, 2024, without language restrictions. After searching the databases, we exported them into Mendeley, and duplicates were removed. One reviewer screened titles and abstracts; the entire paper was reviewed when the title and abstract could not determine study eligibility. All eligible full-text papers were in English. The reference lists from the 7 full texts selected to be included within this study were manually searched to identify studies not found through the electronic database searches. Still, no other texts appropriate to this study were extracted from this search. A Peer Review of Electronic Search Strategies was implemented before conducting the search strategy.⁴¹ The search strategy included 3 strings of key terms joined with AND, and the terms within the strings were joined with OR (Table 2).

Table 2.Search Syntax

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Quality Assessment

One reviewer reviewed all studies for risk of bias using the Physiotherapy Evidence Database (PEDro) Scale (Table 3) adapted from the Delphi list.^42,43

Table 3.PEDro Scale Criteria

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Data Extraction

The inclusion criteria included an electrotherapy intervention in rehabilitating CAI in combination with TEx therapies. The full text of eligible papers was retrieved and reviewed. The following data were extracted: electrotherapy intervention used, exercise therapy used, outcome measures, and findings.

Data Analysis

Due to the heterogeneity of studies, direct comparison and meta-analysis were not possible, so a narrative review was undertaken in line with the synthesis without meta-analysis guidelines.⁴⁴

Stochastic Resonance Stimulation

Authors of 3 studies examined TEx combined with stochastic resonance stimulation (SRS) in participants with AI.^30,33,35 Authors of 2 of these studies used the same pool of participants with functional AI (FAI) and interventions; however, they looked at different outcome measures for balance.^30,33

Ross and Guskiewicz and Ross et al combined SRS stimulation to the lateral soleus (SOL), PL, tibialis anterior (TA), anterior talofibular ligament, and deltoid ligament, combined with 6 weeks of coordination training (CT) in individuals with FAI.^30,33 Participants completed 5 × 10-minute training sessions per week.

Ross and Arnold looked at similar outcome measures to Ross et al but with some changes to the TEx program, in that it was reduced from 6 weeks as per Ross and Guskiewicz and Ross et al to 4 weeks with balance and resistance exercises added.^30,33,35 It should be noted that they combined participants with CAI into the same experimental groups as those who had never previously been injured.

Balance Outcome Measures

Ross and Guskiewicz found improvements in both anterior-posterior (A/P) and medial-lateral (M/L) balance in participants with FAI after a 6-week intervention.³³ Participants who received SRS combined with CT demonstrated greater and earlier improvements in time-to-stabilization (TTS) during single-leg jump landings than those who received CT alone. Specifically, the SRS-CT group improved on both A/P and M/L TTS by week 4, whereas the CT-only group showed smaller improvements and plateaued earlier. These improvements were reported as percentage changes from baseline; no means or SDs were provided. Table 4 provides a summary of percentage improvements and associated outcomes for both groups across test sessions. The control group (CG) made no significant improvements.

Table 4.Summary of the Percentage Change in TTS From Pretest in FAI Participants

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Ross et al found that participants who received SRS combined with CT demonstrated significant improvements in balance outcomes compared with pooled results from the CG and CT-only group.³⁰ Specifically, the SRS group showed significant reductions in A/P and M/L center of pressure velocity (COPvel), M/L center of pressure standard deviation (COPsd), M/L maximum excursion (COPmax), and center of pressure area (COParea). The effect size for A/P COPvel was large, with moderate effects observed for M/L COPvel, COPsd, and COParea and a small effect for COPmax. No significant pretest to posttest changes were observed in the CG or CT-only group. A summary of P values and effect sizes comparing the SRS group with pooled CG and CT results is provided in Table 5.

Table 5.Summary of P Values and Effect Sizes Comparing the SRS Group With Pooled CG and CT-Group Results

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Ross and Arnold found improvement in all balance-related outcome measures in all the groups within their study.³⁵ The magnitude of improvement ranged from small to large, with large effects seen in A/P COPvel by week 4. In comparison, the CT-only group also showed improvements in all 4 outcomes, though all effect sizes were small, except for M/L COPvel at week 2, which reached a small to moderate level. Notably, outcome data were drawn from a combined sample of participants with CAI and those without previous injury, which limits the generalizability of results. However, effect sizes were reported specifically for the CAI subgroup, supporting the added benefit of SRS when used alongside balance training. Table 6 provides a summary of percentage improvements and effect sizes for each group across both time points.

Table 6.Summary of the Percentage of A/P and M/L COPvel Improvements With Effect Size (d)

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Transcutaneous Electrical Nerve Stimulation

Authors of 2 studies examined TEx combined with transcutaneous electrical nerve stimulation (TENS) in participants with FAI and CAI.^25,36 They used different methods of TEx, limiting any comparison between the findings.

Yoshida et al examined the acute effects of combining TEx with TENS on balance in individuals with FAI, specifically during jump landing.³⁶ One group received TEx with concurrent TENS applied to the common peroneal nerve, while the comparison group completed the same TEx protocol without TENS. The exercises were outlined for this study; however, detailed methods for the exercise protocol were limited.

Gottlieb et al had 2 experimental groups within their study in which the participants had CAI.²⁵ They combined balance TEx with TENS in 1 group and with neuromuscular electrical stimulation (NMES, see below) in the other group to assess balance and self-reported outcome measures. In both groups, the assigned electrical stimulation was applied to the peroneal group to compare outcomes. Participants were required to complete 2 to 3 treatment sessions per week, with a total of 12 treatment sessions across a 4- to 6-week period at home. It should be noted that the images used to report the Y-Balance Test (YBT) direction described posteromedial (PM) and posterolateral (PostL) the wrong way around, indicating the need for caution when comparing these results with other findings, as the application is not in line with Picot et al, referenced by the authors.⁴⁵

Balance Outcome Measures

Yoshida et al found that balance improved in the TENS with TEx group, as indicated by a significant reduction in the center of pressure (COP) on the affected ankle after the intervention.³⁶ In contrast, the exercise-only group showed no significant change in the COP. These outcomes were observed after just a single therapy session, making it unclear whether the improvements have long-term rehabilitative value. However, the findings suggest potential short-term benefits of combining TENS with exercise, warranting further investigation over the length of a full rehabilitation program. Table 7 presents pre-post means ± SDs for the COP in both groups.

Table 7.Summary of Pre-Post COP Measures for TEx-Only and TENS With TEx Groups

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Gottlieb et al did not observe any significant changes in balance, as indicated by the YBT scores and TTS during a single-legged drop jump (SLDJ) in the TEx-TENS group from baseline to posttreatment.²⁵ Effect sizes are discussed in comparison with NMES below. Table 8 provides a list of baseline-post means ± SDs and effect sizes for each respective group for outcome measures related to balance.

Table 8.Summary of Means ± SDs and Effect Sizes (d) for Outcome Measures

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Patient Self-Reported Outcome Measures

Gottlieb et al found significant improvements in the self-reported outcome measures at 12 months postintervention for the TEx-TENS group, these measures being the Cumberland Ankle Instability Tool (CAIT), the Sports component of the Foot and Ankle Ability Measure (FAAM_sport), and the Identification of Functional Ankle Instability (IdFAI).²⁵ Effect sizes are discussed in comparison with NMES below. Table 8 provides a list of baseline-post means ± SDs and effect sizes for each respective group for outcome measures related to self-reported outcomes.

Transcranial Direct Current Stimulation

Authors of only 1 study examined TEx combined with transcranial direct current stimulation (aTDCS) in participants with CAI.³²

Bruce et al combined aTDCS and eccentric strength training for participants with CAI.³² They allocated the participants to 2 groups, the first combining aTDCS and an eccentric strengthening program using an isokinetic dynamometer and the second completing the eccentric-only program with a sham intervention. The program lasted 4 weeks, and 10 sessions were completed per participant.

Motor Control Outcome Measures

Significant improvements were found in motor control of the PL as indicated by the primary motor cortex excitability resting motor threshold (RMT) and intensity at peak slope (I₅₀). These improvements were found in RMT from week 2 to week 6 (P = .024) in the aTDCS group and I₅₀, in which week 6 values were lower than baseline (P = .025) and week 4 (P = .001). No significant changes were noted in the sham group from baseline to week 6; however, it should be noted that significant improvements were found at week 2 in comparison with the baseline (P = .007), in which an increased excitability was seen; this then decreased again at all other time points but not quite as low as baseline. No significant difference was found in RMT and I₅₀ for the TA. Table 9 provides a list of baseline-post means ± SDs for each respective group for outcome measures related to motor control.

Table 9.Summary of Means ± SDs for Outcome Measures

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Balance Outcome Measures

Improvements in balance, as indicated by the Postural Stability Indices, were observed in the aTDCS group from baseline to week 6 (P = .010), while no significant change was found between any other time points and in the sham group. However, individually, the Anteroposterior Stability Index (APSI), Mediolateral Stability Index (MLSI), Vertical Stability Index (VSI), and composite Dynamic Postural Stability Index (DPSI) found no significant differences between any time points for both groups. Changes in muscle activation were noted in balance-based tasks; this is discussed in the next section. Table 9 provides a list of baseline-post means ± SDs for each respective group for outcome measures related to balance.

Muscle Activation Outcome Measures

Changes in muscle recruitment were also noted during a hop-to-stabilization task. Tibialis anterior activity at 250 milliseconds prelanding decreased significantly from baseline to posttest in both the aTDCS and sham groups. Tibialis anterior activity in the sham group also decreased significantly at 250 milliseconds postlanding. In contrast, PL activation increased significantly at 250 milliseconds postlanding in the aTDCS group. These findings suggest a possible shift in muscle activation strategy in balance-based tasks, with TA activation decreasing prelanding and PL activation increasing postlanding. No significant changes were found for the SOL in either group. Table 9 provides a list of baseline-post means ± SDs for each respective group for outcome measures related to muscle activation.

Patient Self-Reported Outcome Measures

No significant difference was found in patient self-reported outcomes for either group for the Foot and Ankle Ability Measure Activities of Daily Living subscale (FAAM_ADL), FAAM_sport, and Tampa Scale for Kinesiophobia (TSK). However, the aTDCS group score decreased and improved significantly from week 2 to week 4 (P = .046), as indicated by the Disablement in Physical Activity Questionnaire (DPA), with an increase in score being noted in the sham group occurring from baseline to week 2 (P = .047), meaning a significant worsening occurred here. No other differences were found in either group for the DPA. Table 9 provides a list of baseline-post means ± SDs for each respective group for outcome measures related to patient self-reported outcomes.

Muscle Strength Outcome Measures

No significant differences were found for either group in concentric and eccentric strength in either inversion or eversion between any time points for this study (means and SDs not reported).

Neuromuscular Electrical Stimulation

Authors of 2 studies examined TEx combined with NMES in participants with CAI.^25,31 Some similarities in the TEx programs used were found, in that balance training was included in both studies; however, authors of 1 study also provided strength training within the program.³¹

Choi and Jun incorporated NMES to gastrocnemius (GAS) and flexor digitorum longus (FDL) with a 6-week TEx program, including balance training and strength exercises to treat those with CAI.³¹ Participants were split into 4 groups: CG, TEx only, NMES only, and NMES-TEx combined.

Gottlieb et al had 2 experimental groups within their study, both of which defined the participants as having CAI.²⁵ They combined balance TEx with TENS (see TENS section above) in 1 group and NMES in the other. In both instances, the assigned electrical stimulation was applied to the peroneal group to compare their outcomes. Participants were required to complete 2 to 3 treatment sessions per week, with a total of 12 treatment sessions across a 4- to 6-week period at home. It should be noted that the images used to report the YBT direction described PM and PostL the wrong way around, indicating the need for caution when comparing these results with other findings, as the application is not in line with Picot et al, referenced by the authors.⁴⁵

Muscle Strength Outcome Measures

Choi and Jun found that a significant increase in muscle strength occurred in all groups except the CG, as indicated by an increase in thickness of the FDL, medial head of the gastrocnemius (GAS-M), lateral head of the gastrocnemius (GAS-L), and SOL, all with large effect sizes, with the cross-sectional areas (CSAs) of the FDL, GAS-M, GAS-L, and SOL all also significantly increasing with large effect sizes.³¹ However, no significant differences were found for any group for flexor hallucis longus in both muscle thickness and CSA. Table 10 provides a list of baseline-post means ± SDs and effect sizes for each respective group for outcome measures related to muscle strength.

Table 10.Summary of Means ± SDs and Effect Sizes (d) for Outcome Measures

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Balance Outcome Measures

Choi and Jun found dynamic balance significantly improved, as indicated by improvements for all groups except for the CG in YBT scores in all directions: anterior (ANT), PM, and PostL, from pretesting to posttesting as well as composite YBT scores, all with a large effect size.³¹ Improvements in dynamic balance were observed further, as indicated by the Square Hop Test (SHT) with all groups, except for the CG, significantly improving their speed to complete the SHT from pretest to posttest, again all with large effect sizes. Table 10 provides a list of baseline-post means ± SDs and effect sizes for each respective group for outcome measures related to muscle strength.

Gottlieb et al found no significant changes were observed in balance, as indicated by the YBT scores and TTS during an SLDJ in the NMES group from baseline to posttreatment.²⁵ The magnitude of improvement ranged from small to moderate based on the respective effect sizes in favor of the TEx-NMES group compared with the TEx-TENS group. Table 8 provides a list of baseline-post means ± SDs and effect sizes for each respective group for outcome measures related to muscle balance.

Patient Self-Reported Outcome Measures

Gottlieb et al found significant improvements were observed in the self-reported outcome measures at 12 months postintervention in comparison with the baseline; these measures were the CAIT, FAAM_sport, and IdFAI.²⁵ The magnitude of improvement ranged from small to moderate based on the respective effect sizes in favor of the TEx-NMES group compared with the TEx-TENS group. Table 8 provides a list of baseline-post means ± SDs and effect sizes for each respective group for outcome measures related to muscle balance.

Balance Outcome Measures

Some variation in findings was observed when looking at balances as an outcome measure. In all studies in which SRS was combined with TEx, 1 of the 2 studies in which TENS was used with TEx, the study in which aTDCS was combined with TEx, and 1 of the 2 studies in which NMES was combined with TEx, significant improvements in balance-related outcome measures were found, with a majority consensus suggesting electrotherapies may affect rehabilitation positively.^{30,31,33,35,36}

Muscle Strength Outcome Measures

Authors of 2 studies specifically looked at muscle strength in their outcome measures. Authors of 1 found significant improvements, and authors of the other did not. They implemented different electrotherapies with TEx, so comparison here is challenging, but the consensus sways toward positive outcomes because of electrotherapy application, with further research needed.^31,32

Patient Self-Reported Outcome Measures

Some variation in findings was found when looking at patient self-reported outcome measures. Authors of 1 study found positive outcomes for both TENS and NMES combined with TEx.²⁵ Authors who looked at aTDCS found significant improvements in 1 of the DPAs but not in the other methods that they implemented.³² Further research is certainly needed here to ascertain these findings.

Motor Control and Muscle Activation Outcome Measures

Authors of only 1 study specifically looked at motor control and muscle activation, combining TEx with aTDCS.³² Positive outcomes were found in motor control for the PL but not the TA, and muscle recruitment strategies were seen preintervention to postintervention in both muscles, suggesting a positive influence of aTDCS with the need for further research certainly needed here to observe these outcome measures further with aTDCS and with other alternative applications of electrotherapy combined with TEx.

Authors of all the studies discussed in this review applied relatively low-impact TEx programs in their methods, and all the exercises presented within these studies arguably have a place in the rehabilitation of CAI. However, sport is rarely low impact, particularly when it comes to the mechanisms of injury for ankle sprain. Further consideration is needed, as recommended by Wagemans et al, for rehabilitation programs to reflect the established mechanisms of reinjury of ankle sprain to help prevent future reoccurrences.⁴⁶ Therefore, future research in which higher impact and more functional rehabilitative techniques are compared both with and without the application of electrotherapy would be beneficial to assess functional outcome measures and long-term effects on the reoccurrence of injury and therefore the incidences of CAI occurring.

Authors of only 1 of the 7 studies observed any long-term outcome measures after their intervention.²⁵ The outcome measures observed over a more extended period here were self-reported outcome measures by the participants, which benefit from the perceived nature of how participants see their function but do not allow for an understanding of any functional changes that could be observed after the posttest findings. It would be beneficial for future researchers to observe the long-term outcomes of the interventions used to determine if any long-term, lasting positive effects of the combined use of electrotherapies and TEx exist. None of the authors followed up to assess if their interventions affected injury reoccurrence rates.

Limitations

Some of the search terms used in this study may have been too broad, such as “ankle” and “interferential,” which may explain the large number of papers found in our initial search process.

The studies presented in this review were heterogeneous; thus, conclusions about the effectiveness may be limiting.