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Changes in Postural Control due to Electrical Stimulation Therapy for Ankle Instability: A Systematic Review

Document Type : Systematic Reviews

Authors

1 Department of Orthotics and Prosthetics, School of Rehabilitation Sciences, Isfahan University of Medical Sciences, Isfahan, Iran

2 Head of rehabilitation medicine, Erfan hospital, Tehran, Iran

3 PhD of Orthotics and Prosthetics, Associate professor of Orthotics and Prosthetics, Department of Orthotics and Prosthetics, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran.

4 Department of Medical Education and Office of Research, Kirk Kerkorian School of Medicine at UNLV University of Nevada, Las Vegas

5 Technical Services Directorate, MSI Nigeria Reproductive Choices, Abuja, Nigeria.

6 Orthopedic surgean, khatam- Alanbia hospital, orthopedic department, Tehran, Iran

7 Department of Clinical Research and Development, LUXMED Group, Warsaw, Poland; Henry JN Taub Department of Emergency Medicine, Baylor College of Medicine, Houston, TX 77030, USA

8 Department of Clinical Research and Development, LUXMED Group, Warsaw, Poland;

9 Laboratory of «Morocco: history, Theology and languages», Department of Psychology, Faculty of Arts and Human Sciences Fès-Saïss, Sidi Mohamed Ben Abdellah University, Fez- Morocco

10 Laboratory of «Morocco: history, Theology and languages», Department of Psychology, Faculty of Arts and Human Sciences Fès-Saïss, Sidi Mohamed Ben Abdellah University, Fez-Morocco

11 Exercise Medicine Unit, Istituto Auxologico Italiano, IRCCS, Milan, Italy

12 MD, Exercise Medicine Unit, Istituto Auxologico Italiano, IRCCS, Milan, Italy.

13 Department of Psychology, Ağrı İbrahim Çeçen University, Turkey

14 Graduate Studies and Research, Lebanese American University, Beirut, Lebanon

15 Post-graduate School of Occupational Health, Università Cattolica del Sacro Cuore, Rome, Italy.

16 Orthopedic surgeon, Center for Orthopedic Trans-Disciplinary Applied Research, Tehran University of Medical Sciences, Tehran, Iran

10.30476/jrsr.2024.102704.1486

Abstract

Background
Ankle instability results in sensory and motor impairments. Typically, health professionals recommend conservative treatment as the initial approach for individuals with this condition. One such treatment option is Electrical Stimulation (ES). This systematic review assesses the effects of ES techniques on postural control measures in cases of ankle instability.
Method
We systematically searched five electronic databases: ClinicalTrials.gov, PubMed, Scopus, SPORTDiscus, and Web of Science. To evaluate the quality of the included articles, we utilized the PEDro checklist. We extracted data on population, intervention, and outcomes and synthesized them narratively.
Result
ES decreased the time needed to stabilize the center of pressure, velocity, displacement, and area, thereby enhancing the performance of clinical tests. While postural stability indexes remained unaffected, the gait inversion angle increased with electrical stimulation.
Conclusion
These results suggest that ES interventions are crucial in enhancing postural control in subjects with ankle instability compared to coordination exercises therapy alone. Stochastic resonance reduced A/P and M/L TTS, COP velocity, COP displacement, and COP area, resulting in enhanced postural control.
 

Highlights

Hanieh Khaliliyan: googel scholar

mahmood bahramizadeh :googel scholar

Keywords

Introduction

Globally, approximately 712,000 people experience ankle sprains daily [ 1 ]. Despite its significant impact on healthcare, an ankle sprain is often perceived as an insignificant injury that should heal quickly with minimal intervention [ 2 ]. However, in 70% of cases, symptoms such as giving way and recurring sprains can occur even after the acute symptoms have disappeared [ 3 ]. These issues, either independently or combined, can lead to ankle instability. This instability may adversely affect the quality of life [ 4 ] and physical function [ 5 ] and increase the risk for early onset of ankle osteoarthritis [ 6 ].

Ankle instability is a complex syndrome with an unknown cause [ 7 ]. Some researchers propose that it is a neurophysiological disorder resulting from mechanical and functional instability [ 8 ]. However, not all individuals with ankle instability experience mechanical instability following an acute sprain . Many attribute the functional dysfunction in ankle instability to a reduction in mechanoreceptors within the injured ankle joint, leading to deficits in proprioception [ 11 ]. In elite sports such as dancing, football, and gymnastics, ankle proprioception has demonstrated the strongest correlation with competition level compared to other joints, with a correlation coefficient of 0.45 (P<0.001) [ 12 ]. Recent studies have discovered that individuals with ankle instability exhibit impairments in the motor output patterns of their lower limbs before heel contact during walking [ 13 ] and before landing during a drop landing [ 14 , 15 ]. These findings suggest that ankle instability not only leads to sensory deficiencies but also results in changes in motor control.

Systematic studies investigating various aspects of ankle instability, such as deficits in peroneal muscle reaction time and strength [ 16 ] and the kinetics and kinematics of gait and running [ 17 ], have yielded inconsistent results. The only factor firmly established as a significant contributor to ankle instability is impaired postural control [ 18 , 19 ].

Sensory interventions targeting afferent input could improve postural control [ 20 ]. This improvement could arise from the refinement of motor skills, including muscle activity, joint angle, and velocity, either through explicit involvement of the cortico-striatal system, which encompasses both conscious and unconscious proprioception, or through implicit engagement of the cortico-cerebellar system, which is associated with unconscious proprioception [ 21 ]. Various electrical stimulation modalities have been utilized to induce sensory adaptations [ 22 - 27 ]. Electrical current specifically adjusts sensory input through these interventions [ 23 ]. In recent years, researchers have been working to identify rehabilitative interventions that can modify postural control in individuals with ankle instability by manipulating sensory input [ 20 , 28 ]. However, improving postural control remains a topic of debate in ankle instability rehabilitation [ 29 ]. This systematic review aimed to evaluate the effects of electrical stimulation techniques on postural control measures in patients with ankle instability. Our hypothesis suggested that considering their potential impact on improved sensory input and muscle strength, changes in postural control would be noticeable among this cohort.

Methods

Bibliographical Databases and Search Strategy

We conducted this review using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart. Five electronic databases, including ClinicalTrials.gov, PubMed, Scopus, SPORTDiscus, and Web of Science, underwent a systematic search on January 25, 2024, to retrieve scientific literature published in peer-reviewed journals. The search query was constructed based on Population, Intervention, Comparison, and Outcome items. We used Boolean logical operators (“OR” and “AND”) to connect the keywords. We sourced the keywords from the principal author (M.B.) and obtained their synonyms from the medical subject heading database. These keywords included “ankle instabilit*”, “ankle injur*”, “ankle sprain”, “ankle strain”, “electrical stimulation”, “postural control”, “balance”, “postural stability”, “postural equilibrium”, “single leg stance test”, “hop test”, “star excursion balance test”, “jump height”, “agility”, and “center of pressure”.

Eligibility Criteria

Original peer-reviewed studies (such as randomized controlled trials, cross-sectional studies, and case-control studies) conducted anywhere and published between 2000 and 2024 were considered eligible. Participants were young subjects aged 18 to 30 years with ankle instability, based on the International Ankle Consortium statement criteria [ 30 ]. The intervention included electrical stimulation. The trial condition was compared with a control condition that included pre-treatment, conventional treatment, or no treatment. The outcomes were variables that correlated with the postural control concept and were measured with laboratory devices or clinical tests. Studies in the form of expert opinions, case reports, conference papers, animal studies, abstract-only studies, and letters to the editor were excluded.

Study Selection

We evaluated all articles obtained from the database searches for eligibility after identifying and removing duplicates using Endnote20 software. Two separate reviewers (M.A. and M.B.) evaluated the titles and abstracts of the identified articles compared to the selection criteria. Following this, two other reviewers thoroughly scrutinized the remaining articles (H.K. and F.G.).

Risk of Bias Evaluation Tool

Two reviewers (H.K. and M.B.) individually evaluated the methodological quality of each study using the Physiotherapy Evidence Database (PEDro) tool. In the evaluation, a rating of 1 point is allocated for answering “Yes” to each question, whereas 0 point is given for answering “No.” Question 1 (regarding eligibility criteria) is not included in the scoring (Scores <4: poor, 4-5: fair, 6-8: good, and 9-10: excellent) [ 31 ].

Data Extraction

Upon establishing the studies to be included in the review, two reviewers (H.K. and M.B.) independently extracted the total number and demographic characteristics of the population, type, and device characteristics of electrical stimulation, duration and location of electrical stimulation, characteristics of the control condition, and type and statistical measures of outcomes.

Data Synthesis

The results were synthesized based on methodological aspects (outcomes) and clinical factors (population and intervention characteristics). A narrative synthesis of all data elements was performed in a tabular format and discussed in text. The specific P values indicating significance levels from the studies were extracted and presented to discuss potential associations and/or correlations. Conflicts were resolved with input from all authors throughout the entire review procedure.

Results

Search Process and Findings

In the initial search, 218 records were identified, and two additional records were found from the reference lists of included studies. The PRISMA flowchart process led to the inclusion of 11 articles in this review. From the initial search to the final decision, the entire process can be visualized through the PRISMA diagram in Figure 1.

Figure 1. PRISMA diagram depicting the literature review process

Quality Assessment

Two evaluators (H.K. and M.B.) independently appraised the methodological rigor of 11 research investigations by scrutinizing 121 criteria, aligning each study with 11 specific criteria. Initially, they reached a consensus on 111 criteria, indicating a concurrence rate of 92%. The inter-rater reliability assessment utilizing Cohen’s kappa demonstrated nearly flawless accord between the evaluators, yielding a k-coefficient of 0.89 and a 95% confidence interval from 0.840 to 0.920. After further discussion, they achieved 100% agreement. Table 1 displays the quality index scores for each study, with two studies categorized as excellent, five as good, and four as fair. The mean score of 6.63 indicates that the study quality was good overall.

Author, year Eligibility Random criteriaallocation Concealed allocation Similar groups at baseline Subject blinding Therapist blinding Assessor blinding > 85% key outcomes Intention to treat Between- group statistical analysis Point and variability measures Final score
Ross et al., 2006 [32] Yes No No Yes Yes No No Yes Yes Yes Yes 6
Ross et al., 2007 [33] Yes Yes No Yes No No No Yes Yes No Yes 5
Ross et al, 2007 [34] Yes Yes No Yes Yes No No Yes Yes Yes Yes 7
Ross et al., 2012 [35] Yes Yes No Yes No No No Yes Yes No Yes 5
Ross et al, 2012 [36] Yes Yes No Yes Yes No No Yes Yes Yes Yes 7
Glass et al., 2014 [37] Yes No No Yes Yes No No Yes Yes Yes Yes 6
Yoshida, et al, 2015 [38] Yes No No Yes No No No Yes Yes Yes Yes 5
Khalid et al, 2020 [39] Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes 9
Gottlieb et al, 2022 [40] Yes No No Yes No No No Yes Yes Yes Yes 5
Needle et al., 2023 [41] Yes Yes No Yes Yes No Yes Yes Yes Yes Yes 8
Gottlieb et al, 2024 [42] Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes 10
Table 1. PEDro’s assessment result

Across the eleven studies analyzed, all investigations established eligibility criteria, ensured baseline similarity across groups, collected primary outcome data from over 85% of initially enrolled participants, utilized intention-to- treat analysis, and provided point estimates and measures of variability. Additionally, 63.63% of the studies employed random allocation, 18.18% used concealed allocation [ 39 , 42 ], 63.63% implemented subject blinding [ 32 , 34 , 36 , 37 , 39 , 41 , 42 ], 18.18% applied blinding for therapists [ 39 , 42 ] and assessors [ 41 , 42 ], and 81.81% conducted between-group analysis [ 32 , 34 , 36 - 42 ].

Study Characteristics Population

In the selected studies, 403 participants underwent examination. This group consisted of 309 individuals with ankle instability and 90 healthy controls. The participants had an average age of 23.47 years, an average weight of 72.32 kg, and an average height of 172.79 cm. Table 2 summarizes the characteristics of each study’s participants.

Author, year n Groups Male / female Mean age (years) Mean weight (kg) Mean height (cm)
Ross et al., 2006 [32] 60 TG1:20, TG2:20, CG:20 N/C 20.83 74.83 173.33
Ross et al., 2007 [33] 30 TG1:10, TG2:10, CG:10 14/16 21 76 177
Ross et al, 2007 [34] 12 TG: 12 6/6 22 71 173
Ross et al., 2012 [35] 96 TG1:36, TG2:36, CG:24 48/48 21 75 176
Ross et al, 2012 [36] 12 TG: 12 5/7 21 69 173
Glass et al, 2014 [37] 24 TG: 24 12/12 22.5 66.5 172
Yoshida et al, 2015 [38] 7 TG: 7 7/0 20.3 N/C N/C
Khalid et al, 2020 [39] 60 TG1:20, TG2:20, CG:20 60/0 25.8 69.13 166.66
Gottlieb et al, 2022 [40] 48 TG:24, CG:24 30/18 30.25 73 172.5
Needle et al., 2023 [41] 20 TG1:11, TG2: 9 12/8 22.75 73.75 170.95
Gottlieb et al, 2024 [42] 34 TG1:14, TG2:15 14/20 30.8 75 173.5
N/C: No Comment, TG: Trial Group, CG: Control Group
 Table 2. Participants characteristics

Intervention

The included research utilized stochastic resonance [ 32 - 37 ], functional electrical stimulation [ 40 ], neuromuscular electrical stimulation [ 41 , 42 ], and transcutaneous electrical nerve stimulation [ 38 , 39 , 41 , 42 ]. Electrical stimulation is commonly used to change sensory input by adjusting specific stimulus parameters such as pulse pattern, location, frequency, and amplitude [ 37 , 38 ].

In five investigations [ 32 - 36 ], stochastic resonance stimulation was characterized by Gaussian white noise with a zero mean, a standard deviation of 0.05 mA, and band-pass filtering below 1000 Hz. The targeted anatomical locations included the lateral soleus, peroneus longus, tibialis anterior muscles, and mediolateral ankle ligaments. In a separate study [ 37 ], a LabVIEW program generated white noise ranging from 0 to 100 Hz at sensory thresholds of 25%, 50%, 75%, and 90%. The generated signal branched to four tactors to stimulate the gastrocnemius, peroneus longus, and tibialis anterior and posterior muscles.

In another study [ 38 ], researchers administered a transcutaneous electrical nerve stimulation intervention with an amplitude of 4.8 mA and a frequency of 10 Hz. They utilized an Intellect Mobile Stim device and placed a 5×5 cm electrode at the distal end of the fibula to target the common peroneal nerve.

The functional electrical stimulation system [ 40 ], NESS L300Plus, comprises three interconnected components that communicate wirelessly. These components include (1) a stimulator, (2) a gait sensor positioned beneath the heel, and (3) a control unit used to stimulate the peroneus longus muscle belly. The waveform produced by the NESS L300Plus system is symmetrical and biphasic, with a frequency of 35 Hz and a pulse duration of 200 µs. In other studies [ 39 , 41 , 42 ], researchers used a portable device equipped with adhesive surface electrodes to administer transcutaneous electrical nerve stimulation (TENS) and neuromuscular electrical stimulation (NMES). They employed a bi-phasic square wave pattern and targeted different anatomical locations, including the sciatic nerve (1 mA, 75 Hz) [ 41 ], the lateral aspect of the shin (35 Hz for NMES, 10 Hz for TENS) [ 42 ], and the triceps surae muscle (50 Hz) [ 39 ].

Comparisons

Six studies compared a specific form of electrical stimulation involving stochastic resonance and transcutaneous electrical nerve stimulation to coordination exercises [ 32 , 33 , 35 , 38 ] and stretching exercises [ 39 ]. One study investigated different stochastic resonance thresholds [ 37 ], while the other studies compared electrical stimulation with each other [ 41 , 42 ] or with a control condition without any intervention [ 40 ].

Outcomes

Time to Stabilization (TTS)

Out of the 11 studies, three utilized Center of Pressure (COP) Time to Stabilization (TTS) to assess postural control [ 32 , 36 , 42 ]. Applying Stochastic Resonance (SR) to ankle muscles and mediolateral ligaments reduced anteroposterior (A/P) (F(3,108)=4.27, P=0.01, effect size=0.4) and mediolateral (M/L) (F(3,108)=8.02, P<0.01, effect size=0.3) TTS compared to coordination exercise and no intervention after six weeks. Post hoc analysis using Tukey’s Honestly Significant Difference test revealed a notable enhancement of TTS by 22% due to stochastic resonance [ 32 ]. Nevertheless, the evaluation of the immediate impact of stochastic resonance indicated a reduction in A/P TTS (1.32±0.31 s compared to 1.74±0.8 s, t(11)=-2.04, P=0.03), while the M/L TTS (1.95±0.4 versus 1.92±0.48, t(11)=-0.2, P=0.42, d=-0.07) remained unaltered. The mean percentage of instant enhancement for A/P TTS utilizing stochastic resonance was 24% [ 36 ]. There was no significant effect on TTS between applying transcutaneous electrical nerve stimulation and neuromuscular electrical stimulation on the lateral side of the shin (1.2±0.8 compared to 2±2.8, effect size (95% CI): -0.26 (-1.04, 0.52)) [ 42 ]. An effect size equal to 0.2 is considered small, 0.5 is seen as moderate, and 0.8 is classified as large.

COP Velocity

Among the three groups - coordination training, stochastic resonance, and no intervention - there was a significant interaction between treatment and test (Wilk’s Lambda=0.78, F=2.08, P=0.04, η2P=0.12) [ 35 ]. When stochastic resonance was applied to the ankle muscles and ligaments, there was a reduction in posttest A/P (2.3±0.4 cm/s compared to 2.7±0.6 cm/s, t(27)=1.88, P=0.036) and M/L (2.6±0.5 cm/s compared to 2.9±0.5 cm/s, t(27)=1.71, P=0.049) COP velocity compared to pretest [ 33 ]. The stochastic resonance group had positive responses of 75% (A/P at week 2), 88% (A/P at week 4), 83% (M/L at week 2), and 88% (M/L at week 4) [ 35 ]. When comparing stochastic resonance with 25%, 50%, 75%, and 95% sensory thresholds, a main effect for treatment (Wilks’ lambda=0.57, F(5, 18)=2.77, P=0.05; Cohen’s f=0.83) was found. At a sensory threshold of 25%, resultant COP velocity decreased (no stochastic resonance: 0.94±0.32 cm/s, 25%: 0.80±0.19 cm/s, 50%: 0.88±0.24 cm/s, 75%: 0.94±0.25 cm/s, 95%: 1.00±0.28 cm/s). It was found that the 25% sensory threshold stochastic resonance made single-legged balance better than no stochastic resonance by 17% to 10% for COP frontal- and sagittal- plane velocity assessments (P<0.05) [ 37 ].

COP Displacement

Stochastic resonance significantly changed M/L COPsd (0.63±0.12 cm versus 0.73±0.11 cm, t(27)=- 2.37, P=0.013) and M/L COP maximum excursion (1.76±0.25 cm versus 1.98±0.25 cm, t(27)=2.29, P=0.015) compared to the pooled means of pre- intervention (P<0.05) [ 33 ]. A significant enhancement in COP resultant vector by 8.29% was observed with effective stochastic resonance stimulation compared to the control condition (6.60±1.06 cm/s compared to 7.20±1.03 cm/s, t(11)=5.17, P<0.01, effect size=0.56) [ 34 ]. In the transcutaneous electrical nerve stimulation group, the length of the COP on the sprain side notably decreased, measuring 627.0±235.4 mm prior and 551.8±172.1 mm after the activity [ 38 ].

COP Area

The stochastic resonance decreased COP area (0.13±0.03 cm2 versus 0.16±0.04 cm2, t(27)=1.79, P=0.043) compared to the means of pre-stochastic resonance (P<0.05) [ 33 ]. There was no difference in COP area for different stochastic resonance thresholds (25%, 50%, 75%, and 95% sensory thresholds) (F(5, 18)=0.82, P=0.55, Cohen’s f=0.45) [ 37 ].

Clinical Tests

The transcutaneous electrical nerve stimulation group showed a significant increase (P≤0.01) in balance after treatment for anterior (5.4%, P=0.01, η2P=0.61), posterior (4.2%, P=0.01, η2P=0.65), posterolateral (3.9% P=0.01, η2P=0.67), and posteromedial (5.6%, P=0.01, η2P=0.63) directions in the pre- to follow-up period compared to stretching (1.3%, 1.2%, 0.7%, and 0.8%, respectively) [ 39 ]. Significant positive effect sizes were noted in favor of the neuromuscular electrical stimulation group for the star excursion balance test posteromedial direction at post-treatment (Cohen’s d=0.38) with a 95% confidence interval of -0.38 to 1.13 over the transcutaneous electrical nerve stimulation group [ 42 ]. The side hop test showed no significant group (transcutaneous electrical nerve stimulation and neuromuscular electrical stimulation)-by-time (baseline, two weeks, and four weeks) interaction effect (F(2, 36)=0.142, P=0.868) [ 41 ].

Postural Control Indexes

There is no significant difference between applying transcutaneous electrical nerve stimulation or neuromuscular electrical stimulation and the control group in terms of dynamic postural stability index (F=0.079, P=0.924), anteroposterior stability index (F=0.055, P=0.947), mediolateral stability index (F=1.2, P=0.28), and vertical stability index (F=0.5, P=0.611) [ 41 ].

Inversion Angle

A notable disparity within the functional electrical stimulation cohort revealed heightened ankle eversion during 0-7% (P=0.011) and 67-81% (P=0.006) of the stance phase post-intervention. Table 3 outlines the details of each study’s attributes.

Author, year Study design Population Trial and control groups or conditions Duration Assessment protocol and instruments Outcome Conclusion
Ross et al, 2006 [32] Experimental with repeated measures FAI -Single leg coordination exercise 6 weeks Participants underwent evaluation using a unilateral leg jump-landing assessment. The assessment involved performing a jump with both legs at a height between 50% and 55% of their highest jump, while standing 70 cm away from the midpoint of the force plate. Anteroposterior and mediolateral TTS Utilizing SR stimulation could be considered as a viable treatment option for FAI. This is because it has the potential to enhance dynamic postural stability at a faster pace and to a larger degree in contrast to coordination exercises without SR stimulation.
-Single leg coordination exercise with SR stimulation 5day/week
- no intervention 10 min/session
Ross et al, 2007 [33] Pre-post intervention design FAI -Coordination exercises 6 weeks Postural stability of one leg was evaluated through the utilization of a force plate. Data was captured at a rate of 180 Hz and the signals were transmitted them through a BNC adapter chassis. -A/P and M/L COP velocity A six-week coordination practice regimen, which includes SR, has resulted in improved postural stability
-SR with Coordination exercises 5 times/week -M/L COP SD
-no intervention -M/L COP maximum excursion
-COP area
Ross et al, 2007 [34] Cross over FAI - SR Stimulation (0.01 and 0.05 mA) 20 seconds Data was gathered during the assessment of single-leg stance by utilizing a force plate operating at a rate of 180 Hz. The analog signals underwent amplification and were subsequently conveyed through a BNC adapter chassis. COPV-R SR could enhance postural maintenance
-no intervention
Ross et al, 2012 [35] Repeated measured FAI -Balance training 4 weeks Single-leg equilibrium assessments were conducted at three different times: pre-training, 2 weeks, and 4 weeks post-assessment. In order to evaluate dynamic balance, participants executed a unilateral jump-landing maneuver, leaping to a level equivalent to 50-55% of their peak vertical jump, and alighted on a singular leg atop a force platform, subsequently promptly stabilizing their posture. A/P COP velocity SR led to improved sagittal plane stability, while the non-SR group showed improvement after 4 weeks. As for frontal plane stability, SR resulted in enhanced balance after 4 weeks.
-Balance training with SR 5 times/ week M/L COP velocity
-NO intervention 10 min/session
Ross et al, 2012 [36] Cross over FAI -SR condition To assess dynamic balance, participants performed a single-leg jump-landing test. They were given instructions to jump and reach a height between 50% and 55% of their maximum vertical jump. Afterward, they were required to land on one leg on a force plate and quickly stabilize themselves. A/P TTS M/L TTS Health professionals could use SR to improve balance during dynamic single-leg exercises in the frontal-and-sagittal plane. This would allow patients to participate in exercises that may otherwise be difficult for them.
-no SR conditionImmediately
Glass et al, 2014 [37] Case control with a cross over design FAI SR at 25,50,75% of sensory threshold 20 seconds Participants were directed to stand without shoes on one foot on a force platform for 20 seconds. The affected leg needed to be flexed at the knee, while the foot should be in a neutral alignment. The unaffected leg was to be slightly bent at both the hip and knee joints. Data collection commenced upon the participants attaining equilibrium. M/L and A/P COP velocity and excursion R-COPV COP ellipse area 25% sensory threshold SR led to enhancements in single-legged and double-legged balance.
Yoshida et al, 2015 [38] Crossover FAI -Balance training with TENS 1 session Participants were asked to perform a sideways jump over a platform that was 20 cm high. They were instructed to use only one leg and to maintain this position for a duration of 10 seconds. COP length The balance exercises, when combined with TENS, significantly decreased ankle instability on the sprained side. This decrease can be attributed to the increased activity of the peroneal muscles, which is a result of the shared innervation from the common peroneal nerve.
-Balance training 3times Peroneal muscle EMG
Each time 10min
5 min rest between times
40 min TENS
Khalid et al, 2020 [39] Randomized controlled trial FAI -The PNF technique 5 weeks During the pretreatment, posttreatment in the third week, and follow-up at the start of the fifth week, all three groups underwent assessment. They used the SEBT to evaluate dynamic postural control. The SEBT consists of 8 directions set at 45-degree angles from the center. The primary measurement in this evaluation is the maximum distance a limb can move in any direction without losing balance. SEBT It was observed that a treatment program involving triceps sural muscle PNF stretching in combination with TENS, which induced muscle contraction during the PNF stretch phase, led to substantial improvements in balance compared to PNF stretching alone.
-TENS and PNF 4 times per week
-No intervention
Gottlieb et al, 2022 [40] Repeated measured crossover CAI -FES 10 min Ankle angles in the sagittal plane were determined while walking through the utilization of the Cardan rotation order. A motion tracking setup comprising eight cameras documented ankle motions in three dimensions at a frequency of 100 Hz. Subsequently, the information underwent analysis in Visual 3D application employing a six-degree-of-freedom anatomical model. Peroneal EMG readings were obtained utilizing a wireless EMG device operating at 2000 Hz. Ankle inversion angle The results indicate that peroneal FES can induce changes in ankle movements during walking. This has the potential to inform future interventions for individuals with CAI.
-no FES Peroneal EMG
Needle et al, 2023 [41] Randomized controlled trial CAI NMES 2 weeks intervention Baseline, post-intervention (following a 2-week period), and retention assessments (after 4 weeks) were carried out. EMG of the PL, TA, and SOL muscles were performed during MVC. Competition time of hop test TENS had some impact on neural excitability, but it did not significantly affect clinical functionality. While TENS shows promise for neuromodulation, it may require the addition of rehabilitative exercises to bring about lasting changes.
TENS 5 sessions Participants' maximal jump height was assessed utilizing a Vertec jump trainer. Participants executed forward hops from a 70 cm distance towards a force plate integrated into the floor, achieving a vertical height equivalent to 50% of their maximal jump. EMG of PL, TA, and SOL muscles the anteroposterior, mediolateral, and vertical directions Stability indexes, and combined dynamic postural stability index
10 min per session Functional performance was gauged through a single-leg lateral hop test.
4 weeks retention
Gottlieb et al, 2024 [42] Randomized controlled trial CAI Training with NMES 4-6 weeks The experimental groups were assessed at baseline, pre-intervention, post-intervention, follow-up at 6 months, and at 12 months. Participants were tasked with executing a unilateral drop-jump from a raised platform of 25 cm height onto a force plate measuring 50 × 60 × 5 cm, produced by Kistler in Switzerland. Following the landing, participants were directed to promptly regain stability and sustain equilibrium for a duration of 20 seconds. SEBT The consistent pattern of enhanced functional results observed with the combination of NMES and training, as opposed to training with TENS, suggests a potential advantage that warrants additional exploration as a therapeutic approach for individuals with CAI.
Training with TENS 12 sessions TTS
6min
TTS: Time To Stabilization; FAI: Functional Ankle Instability; SR: Stochastic Resonance; A/P: Anteroposterior; M/L: Mediolateral; COP: Center Of Pressure; TA: Tibialis Anterior; SD: Standard Deviation; COPV-R: COP Vector- Resultant; CAI: Chronic Ankle Instability; LS: Lateral Soleus; PL: peroneus longus; ATFL: anterior talofibular ligament; PNF: proprioceptive neuromuscular facilitation; SEBT: Star Excursion Balance Test; MVC: Maximum Voluntary Contracture; GRF: Ground Reaction Forces; Electromyography: EMG; SOL: Soleus
Table 3. Study characteristics

Discussion

This review explores the potential benefits of electrical stimulation for improving postural stability in individuals with ankle instability. Studies show that people with ankle instability have a shorter reach distance on the star excursion balance test [ 43 ], longer durations on hop tests [ 43 ], and larger center of pressure (COP) excursion parameters [ 44 ]. Our review showed that applying electrical stimulation can reduce COP Time to Stabilization (TTS) [ 32 , 36 , 42 ] and velocity [ 33 , 35 , 37 ] in the anteroposterior (A/P) and mediolateral (M/L) directions. Additionally, COP displacement [ 34 , 38 ] and area [ 33 , 37 ] were significantly reduced with electrical stimulation, leading to improved clinical test performance [ 39 , 41 , 42 ]. While electrical stimulation did not affect postural stability indexes [ 41 ], it did increase the eversion angle during gait [ 40 ].

One possible reason for these impacts might be the increased muscle activity caused by electrical stimulation, as mentioned in previous discussions on anterior cruciate ligament injuries [ 45 ]. Electrical stimulation activates specific muscle nerves, leading to muscle contractions [ 46 , 47 ]. It is thought to arise from the disinhibitory impacts of heightened activation of afferent fibers [ 48 ]. The strength of the peroneal muscles could be essential in preventing recurrent ankle sprains by assisting in ankle eversion, especially when the foot is susceptible to rolling [ 49 ]. Electrical stimulation applied to the common peroneal nerve influenced the dorsal motor area, increasing activity in the primary motor cortex [ 50 ]. Additionally, the peroneal muscles exhibited heightened activity due to the common peroneal innervation induced following the methodology detailed by Wu et al. [ 51 ]. Another study demonstrated enhanced pinch force in stroke patients following transcutaneous electrical stimulation [ 52 ]. Participants with ankle instability had a higher bilateral peroneus longus resting motor threshold. Elevated resting motor threshold levels may indicate impaired peroneus longus corticomotor excitability in individuals with ankle instability. The correlation between resting motor threshold and self-reported function was moderate, suggesting that deficiencies in corticomotor excitability could impact functional abilities [ 53 ].

When contemplating the application of electrical stimulation to individuals with ankle instability, the potential impacts extend beyond neural excitability [ 41 ]. Two reviews indicated that treatment strategies incorporating balance exercises effectively improve the functionality of individuals with ankle instability. For this reason, the included studies used electrical stimulation in combination with exercise therapy . Prioritizing proprioceptive rehabilitation following an ankle injury is crucial, given the potential spinal and supraspinal adaptations thought to result from a lack of proprioception in the ankle joint [ 48 ].

One detrimental effect of electrical stimulation could be muscle fatigue. Electrical stimulation can reduce muscle fatigue by modifying various elements such as stimulation parameters, training duration, and electrode size and placement [ 56 ]. Prior research has utilized various durations of functional electrical stimulation, ranging from under one minute to 15 minutes . We could infer that using a briefer training period might have reduced muscle fatigue [ 57 ]. Increasing stimulation intensity gradually during the electrical stimulation (ES) session could lead to improved adaptation and postpone the onset of muscle fatigue [ 58 ]. Employing multiple electrodes with asynchronous activation sequences represents an alternative approach to reducing muscle fatigue while applying electrical stimulation. In this review, certain studies employed electrodes of considerable size (50 cm2) for delivering the stimulation [ 40 ], while others utilized smaller dimensions. Although larger electrodes might cause reduced discomfort, they could engage a more extensive array of motor units, potentially leading to earlier fatigue onset [ 40 ].

Limitations

In previous studies, a comprehensive analysis of the optimal timing, frequency, and amplitude for applying electrical stimulation appeared to be lacking. Additionally, no comparative study has been conducted to determine the best type of electrical stimulation. It is necessary to acknowledge that the studies were conducted within controlled laboratory settings, thus casting doubt on the transferability of these interventions’ effects to real-world performance.

Conclusion

The application of electrical stimulation significantly impacts postural control measures compared to coordination exercises and no intervention in ankle instability. Stochastic resonance led to a reduction in anteroposterior (A/P) and mediolateral (M/L) Time to Stabilization (TTS), center of pressure (COP) velocity, COP displacement, and COP area, resulting in enhanced postural control. Notably, at a 25% sensory threshold, stochastic resonance showed the most consistent improvements in postural control parameters. Additionally, the transcutaneous electrical nerve stimulation group demonstrated improved postural control outcomes in various directions compared to stretching exercises. The neuromuscular electrical nerve stimulation group also positively affected specific postural tests. Further research and clinical trials may provide deeper insights into these interventions’ long- term effectiveness and applicability for ankle instability.

Acknowledgment

None

Conflict of Interest

None declared.

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Journal of Rehabilitation Sciences & Research
Volume 11, Issue 3
September 2024
Pages 117-126
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