The effects of visual feedback disruption on postural control with chronic ankle instability

Postural stability measures as diagnostic tools for chronic ankle instability: a comprehensive assessment

BACKGROUND

Chronic ankle instability (CAI) is characterized by recurrent sprains and persistent symptoms, which impair postural control. This study evaluates the diagnostic utility of various linear and nonlinear postural stability measures in distinguishing individuals with CAI from healthy controls.

METHODS

Postural stability was assessed in 24 participants (12 with CAI and 12 healthy controls) using a force platform under four conditions: hard surface with eyes open, hard surface with eyes closed, soft surface with eyes open, and soft surface with eyes closed. Linear measures of center of pressure (COP) included range in the anteroposterior (Rfa) and mediolateral (Rsw) directions, mean velocity (MV), and sway area. Nonlinear measures included approximate entropy (ApEn), the largest Lyapunov exponent, and correlation dimension (CD) with its standard deviation. Diagnostic accuracy was evaluated using receiver operating characteristic (ROC) analysis to determine cutoff scores, allowing effective differentiation between CAI and healthy participants.

RESULT

AI individuals exhibited increased mediolateral COP sway and higher mean velocity on hard surfaces with both eyes open and closed. On soft surfaces with eyes closed, they showed significant deficits in sway area and mean velocity, reflecting challenges in postural control. ROC analysis revealed that certain linear and nonlinear measures showed strong diagnostic accuracy in distinguishing individuals with CAI from healthy controls. Nonlinear analysis revealed elevated ApEn and reduced CD in CAI participants, indicating greater postural irregularity and reduced dynamic stability. On a hard surface with eyes open both Rsw (cutoff: 1.18 cm, OR: 4.55) and ApEn (cutoff: 0.07, OR: 4.0) were particularly strong diagnostic indicators.

CONCLUSION

Linear and nonlinear postural stability measures effectively differentiate individuals with CAI from healthy controls. Key metrics, including Rsw, MV, ApEn, and CD, offer strong diagnostic value for early detection and personalized rehabilitation. Incorporating these measures into clinical practice may improve CAI management and patient outcomes.

ETHICAL CODE

IR.TUMS.FNM.REC.1400.236. March 14, 2022.

Effects of visual disruption on static and dynamic postural control in people with and without chronic ankle instability

Introduction

Chronic Ankle Instability (CAI) is a chronic syndrome resulting from repeated ankle sprains that lead to persistent dysfunction.the purpose of this study is to determine whether visual disruption could influence static and dynamic postural control in people with and without chronic ankle instability (CAI), with the objective of gaining a comprehensive understanding of the interactions between visual inputs and postural control.

Methods

Thirty people with CAI (21 males and 9 females, age = 22.0 ± 1.8 years, height = 174.4 ± 10.2 cm, body mass = 72.5 ± 15.4 kg; Cumberland Ankle Instability Tool (CAIT) score = 19.7 ± 1.8) and twenty-nine without CAI (24 males and 5 females, age = 22.9 ± 1.6 years, height = 172.8 ± 8.0 cm, body mass = 69.0 ± 11.3 kg; CAIT score = 29.0 ± 0.7) were recruited. Their static and dynamic postural control was measured in two conditions with or without visual disruption, simulated using stroboscopic glasses. Static postural control was measured during single-limb standing and represented by root mean square (RMS) of the plantar center of pressure (CoP), dynamic postural control was measured during a Y-balance test and represented by the relative reach distance. Two-way mixed ANOVA (between group: CAI vs non-CAI, within group: normal vision vs visual disruption) was used to analyze data.

Results and discussion

Significant interactions were detected in the CoP-RMS in the anteroposterior (AP) (p = 0.021, η2 p = 0.090) and mediolateral (ML) (p < 0.001, η2 p = 0.208) directions, and the relative reach distances in the posteromedial (PM) p = 0.023, η2 p = 0.088) and posterolateral (PL) (p = 0.009, η2 p = 0.113) directions, from normal vision to visual disruption. The CoP-RMS in the AP and ML directions significantly increased and the relative reach distances in the PM and PL directions significantly decreased in people with CAI while remaining unchanged in those without CAI. People with CAI are susceptible to visual disruption on postural control, highlighting the importance of visual input in maintaining stable posture in this population.

Noninstrumented Clinical Assessment of Static Postural Stability in Chronic Ankle Instability: A Systematic Review and Meta-Analysis

CONTEXT

Several clinical tests are available to assess static postural stability in individuals with chronic ankle instability (CAI); however, it is unclear which test should be used.

OBJECTIVE

To determine which noninstrumented clinical tests should be used to detect static postural stability deficits in individuals with CAI.

EVIDENCE ACQUISITION

We searched 4 databases from their inception to February 2023, and included studies comparing static postural stability in individuals with CAI and healthy controls using noninstrumented assessments. Two reviewers independently extracted study characteristics, participant information, static postural stability assessment methods, and results. We calculated the pooled standardized mean difference (SMD) and 95% confidence interval using a random effects meta-analysis and assessed the certainty of the evidence.

EVIDENCE SYNTHESIS

Fourteen cross-sectional studies (293 participants with CAI and 284 healthy controls) were included. The meta-analysis showed no significant differences between the CAI and healthy groups in the double-leg stance condition of the Balance Error Scoring System (BESS) (SMD, -0.03; low-certainty evidence). Significant group differences were found in the BESS single-leg stance (SLS) on firm and foam surfaces (SLS firm: SMD, 0.47, very low-certainty evidence; SLS foam: SMD, 0.80, very low-certainty evidence), the tandem stance (TS) on firm and foam surfaces (TS firm: SMD, 0.39, low-certainty evidence; TS foam: SMD, 0.76, low-certainty evidence), and the total BESS in the foam conditions (SMD, 1.12, very low certainty evidence). Significant differences were also found between the CAI and healthy groups in the foot-lift (SMD, 1.24; very low certainty evidence) and time-in-balance tests (SMD, -0.94; very low certainty evidence).

CONCLUSIONS

Due to the large magnitude of the differences, the SLS foam, TS foam, and the total BESS in the foam conditions, as well as the foot-lift test or time-in-balance test, may be the most appropriate to clinically identify static postural stability impairment in individuals with CAI.

Visual Disruption and Neuromechanics During Landing-Cutting in Individuals With Chronic Ankle Instability

CONTEXT

Individuals with chronic ankle instability (CAI) demonstrate altered movement patterns when their vision is disturbed during simple tasks, such as single-legged standing and walking. However, it remains unclear whether visual disruption by stroboscopic glasses alters movement patterns during landing-cutting movements, considered highly demanding sport maneuvers that mimic a typical athletic movement.

OBJECTIVES

To identify altered lower extremity kinematics and muscle activation when vision is disrupted by stroboscopic glasses during landing-cutting tasks in individuals with CAI.

DESIGN

Case-control study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 18 individuals with CAI (age = 22.3 ± 2.3 years, height = 1.75 ± 0.1 m, mass = 72.5 ± 9.8 kg) and 18 matched healthy controls (age = 21.7 ± 2.3 years, height = 1.75 ± 0.1 m, mass = 71.9 ± 10.3 kg).

INTERVENTION(S)

All participants performed 5 trials of a landing-cutting task with (SV) and without (NSV) stroboscopic glasses.

MAIN OUTCOME MEASURE(S)

Frontal- and sagittal-plane lower extremity kinematics and 6 lower extremity muscle activations during the stance phase of a landing-cutting task in the SV and NSV conditions.

RESULTS

Individuals with CAI demonstrated more ankle-inversion angle from 18% to 22% and from 60% to 100% of the stance phase and more peroneus longus activation from initial contact to 18% of the stance phase under the SV condition than under the NSV condition. We observed no differences in knee- and hip-joint angles between the visual conditions for both groups.

CONCLUSIONS

When wearing stroboscopic glasses, individuals with CAI showed altered movement patterns, including increased ankle-inversion angle and peroneus longus activation during the stance phase of a landing-cutting task. The results suggest that they may lack the ability to reweight sensory information to adapt their movement to visual disruption.

Effects of Blood Flow Restriction on Balance Performance During Dynamic Balance Exercises in Individuals With Chronic Ankle Instability

CONTEXT

Blood flow restriction (BFR) is a rehabilitation tool which may introduce a constraint, similar to muscle fatigue, that challenge patients' sensorimotor system during balance exercises. The purpose of our study was to examine whether adding BFR to dynamic balance exercises produced a decrease in balance performance and an increase in ratings of perceived exertion and instability in individuals with chronic ankle instability (CAI) compared with dynamic balance exercises without BFR.

DESIGNS

Crossover design.

METHODS

Our sample included N = 25 young adults with a history of CAI. Participants completed 2 laboratory visits. At each visit, participants completed 4 sets (30×-15×-15×-15×) of dynamic balance exercises, performed similar to the modified star excursion balance test (SEBT), once with BFR and once with control (no BFR) conditions. We measured composite SEBT scores at baseline and during the final repetitions of each set of balance exercise (sets 1-4). We also measured ratings of perceived exertion and instability following each balance exercise set.

RESULTS

We observed no difference in composite SEBT scores between conditions at baseline; however, composite SEBT scores were significantly lower during all balance exercises sets 1 to 4 with the BFR condition compared with control. During the BFR condition, composite SEBT scores were significantly lower during all balance exercise sets compared with baseline. During the control condition, composite SEBT scores did not significantly change between baseline and each balance exercise set. Ratings of perceived exertion and instability scores were significantly greater in the BFR group compared with the control group during all balance exercise sets.

CONCLUSIONS

Individuals with CAI demonstrated lower composite SEBT scores and greater perceived instability and exertion during dynamic balance exercise with BFR compared to without BFR. BFR introduced a novel muscle fatigue constraint during dynamic balance exercises in individuals with CAI. Additional research is needed to determine if adding BFR to balance training could improve clinical outcomes in CAI patients.

Sensory conflicts through short, discrete visual input manipulations: Identification of balance responses to varied input characteristics

Human balance control relies on various sensory modalities, and conflict of sensory input may result in postural instability. Virtual reality (VR) technology allows to train balance under conflicting sensory information by decoupling visual from somatosensory and vestibular systems, creating additional demands on sensory reweighting for balance control. However, there is no metric for the design of visual input manipulations that can induce persistent sensory conflicts to perturb balance. This limits the possibilities to generate sustained sensory reweighting processes and design well-defined training approaches. This study aimed to investigate the effects that different onset characteristics, amplitudes and velocities of visual input manipulations may have on balance control and their ability to create persistent balance responses. Twenty-four young adults were recruited for the study. The VR was provided using a state-of-the-art head-mounted display and balance was challenged in two experiments by rotations of the visual scene in the frontal plane with scaled constellations of trajectories, amplitudes and velocities. Mean center of pressure speed was recorded and revealed to be greater when the visual input manipulation had an abrupt onset compared to a smooth onset. Furthermore, the balance response was greatest and most persistent when stimulus velocity was low and stimulus amplitude was large. These findings show clear dissociation in the state of the postural system for abrupt and smooth visual manipulation onsets with no indication of short-term adaption to abrupt manipulations with slow stimulus velocity. This augments our understanding of how conflicting visual information affect balance responses and could help to optimize the conceptualization of training and rehabilitation interventions.

Effects of textured insoles and elastic braces on dynamic stability in patients with functional ankle instability

BACKGROUND

Functional ankle instability (FAI) is a common condition that affects individuals who have experienced previous ankle sprains. Textured insoles and elastic ankle braces have been previously used as interventions to improve stability in FAI patients. However, the optimal combination of these interventions has not been fully explored. The objective of this study was to investigate the effects of different types of textured insoles and elastic ankle braces on the dynamic stability of individuals diagnosed with FAI.

METHODS

The study involved 18 FAI patients who performed single-leg landing tasks with and without wearing an eight-band elastic ankle brace while wearing textured insoles with protrusion heights of 0 mm, 1 mm, and 2 mm. The dynamic posture stability index (DPSI) and its components in the anterior-posterior (APSI), mediolateral (MLSI) and vertical (VSI) directions were calculated from the ground reaction force collected from the Kistler force plate during the first three seconds of the landing tasks.

RESULTS

A significant interaction was found between textured insole type and ankle brace for DPSI (P = 0.026), APSI (P = 0.001), and VSI (P = 0.021). However, no significant interaction was observed for MLSI (P = 0.555). With elastic ankle braces, textured insoles with 1-mm protrusions significantly enhanced anterior-posterior, mediolateral, vertical, and overall stability compared to textured insoles with no and 2 mm protrusions (P < 0.05). Without elastic ankle braces, textured insoles with 1-mm protrusions significantly improved the anterior-posterior (P = 0.012) and overall stability (P = 0.014) of FAI patients compared to smooth insoles.

CONCLUSIONS

The combination of textured insoles with 1-mm protrusion heights and an elastic ankle brace could enhance the dynamic stability of individuals with FAI, potentially mitigating the risk of ankle sprains.

Disrupted vision impairs force steadiness and accuracy in chronic ankle instability patients

The primary purpose of this study was to examine the effect of visual disruption on submaximal force steadiness and accuracy among three groups including chronic ankle instability (CAI) patients, lateral ankle sprain copers, and healthy controls. Twenty patients with CAI, 20 copers, and 20 matched-healthy controls volunteered to participate in the study. Submaximal force steadiness and accuracy for evertors, invertors, and hip abductors (10% and 20% of their maximal voluntary isometric contraction) were measured with an isokinetic dynamometer. All groups performed the tasks with and without stroboscopic glasses. The CAI group showed worse steadiness and accuracy in evertors with visual disruption compared to nonvisual disruption (p < 0.0001 and = 0.02, respectively). Relative to the control group, the CAI group showed worse force steadiness and accuracy in evertors (p < 0.0001, both), worse force accuracy in hip abductors (p = 0.02), and the coper group also showed worse accuracy in evertors (p = 0.02). Individuals with CAI demonstrated impaired force steadiness and accuracy in evertors and hip abductors compared to healthy controls. In addition, they tended to rely more on visual feedback during the force steadiness task than copers and healthy controls.

Stroboscopic visual training: The potential for clinical application in neurological populations

Visual problems are common in people who have neurological injury or disease, with deficits linked to postural control and gait impairment. Vision therapy could be a useful intervention for visual impairment in various neurological conditions such as stroke, head injury, or Parkinson's disease. Stroboscopic visual training (SVT) has been shown to improve aspects of visuomotor and cognitive performance in healthy populations, but approaches vary with respect to testing protocols, populations, and outcomes. The purpose of this structured review was to examine the use of strobe glasses as a training intervention to inform the development of robust protocols for use in clinical practice. Within this review, any studies using strobe glasses as a training intervention with visual or motor performance-related outcomes was considered. PubMed, Scopus, and ProQuest databases were searched in January 2023. Two independent reviewers (JD and RM) screened articles that used strobe glasses as a training tool. A total of 33 full text articles were screened, and 15 met inclusion/exclusion criteria. Reported outcomes of SVT included improvements in short-term memory, attention, and visual response times, with emerging evidence for training effects translating to balance and physical performance. However, the lack of standardisation across studies for SVT protocols, variation in intervention settings, duration and outcomes, and the limited evidence within clinical populations demonstrates that further work is required to determine optimal strobe dosage and delivery. This review highlights the potential benefits, and existing research gaps regarding the use of SVT in clinical practice, with recommendations for clinicians considering adopting this technology as part of future studies in this emerging field.

Effects of visual deprivation on the injury of lower extremities among functional ankle instability patients during drop landing: A kinetics perspective

Background: The ankle is prone to injury during drop landing with usual residual symptoms, and functional ankle instability (FAI) is the most common. Vision guarantees the postural stability of patients with FAI, and visual deprivation (VD) increases their risk of injury when completing various movements. This study explored injury risk during drop landing in patients with FAI under VD through the kinetics of lower extremities. Methods: A total of 12 males with FAI participated in the study (age, 23.0 ± 0.8 years; height, 1.68 ± 0.06 m; weight, and 62.2 ± 10.4 kg) completed single-leg drop landings under visual presence (VP) and VD conditions. Ground reaction force (GRF), time to peak GRF, joint torque, and vertical length variation (ΔL) were measured. Results: Significant effects were detected in the group for time to peak lateral GRF (p = 0.004), hip extensor torque (p = 0.022), ankle plantarflexion torque (p < 0.001), ankle varus torque (p = 0.021), lower extremity stiffness (p = 0.035), and ankle stiffness (p < 0.001). Significant effects of conditions were detected for vertical GRF, time to peak vertical and lateral GRF, loading rate, hip extensor torque, knee extensor torque, hip varus torque, knee varus torque, lower extremity stiffness, and ankle stiffness (p < 0.05). ΔL was affected by VD with a significant difference (p < 0.001). Conclusion: In patients with FAI, an unstable extremity has a higher injury risk than a stable extremity, and VD increases such risk. However, because the influence of the central nervous system on hip strategy is also affected, the effect on the unstable extremity is more significant and more likely to result in injury. Deepening the squat range may be an effective preventive measure for reducing injury risk of unstable extremities during drop landing.

Adaptations of postural sway dynamics and cortical response to unstable stance with stroboscopic vision in older adults

Background: Stroboscopic vision (SV), intermittent visual blocking, has recently been incorporated into postural training in rehabilitation. This study investigated interactions of postural fluctuation dynamics and cortical processing for the elderly during stabilometer stance with SV.

Methods: Thirty-five healthy elderly maintained an upright stance on a stabilometer. Along with postural fluctuation dynamics, EEG relative power and EEG-EEG connectivity were used to contrast neuromechanical controls of stabilometer stance with SV and full-vision.

Results: Compared with the full-vision, SV led to greater postural fluctuations with lower sample entropy and mean frequency (MF). SV also reduced regional power in the mid-frontal theta cluster, which was correlated to SV-dependent changes in the size of postural fluctuations. SV also enhanced the alpha band supra-threshold connectivity in the visual dorsal and frontal–occipital loops of the right hemisphere, and the supra-threshold connectivity from Fp2 positively related to variations in the MF of postural fluctuations.

Conclusion: SV adds challenge to postural regulation on the stabilometer, with the increasing regularity of postural movements and fewer corrective attempts to achieve the postural goal. The elderly shift over-reliance on visual inputs for posture control with more non-visual awareness, considering deactivation of the dorsal visual stream and visual error processing.

Sinusoidal Optic Flow Perturbations Reduce Transient but Not Continuous Postural Stability: A Virtual Reality-Based Study

Optic flow perturbations induced by virtual reality (VR) are increasingly used in the rehabilitation of postural control and gait. Here, VR offers the possibility to decouple the visual from the somatosensory and vestibular system. By this means, it enables training under conflicting sensorimotor stimulation that creates additional demands on sensory reweighting and balance control. Even though current VR-interventions still lack a well-defined standardized metric to generate optic flow perturbations that can challenge balance in a repeatable manner, continuous oscillations of the VR are typically used as a rehabilitation tool. We therefore investigated if continuous sensory conflicts induced by optic flow perturbations can challenge the postural system sustainably. Eighteen young adults (m = 8, f = 10, age = 24.1 ± 2.0 yrs) were recruited for the study. The VR was provided using a state-of-the-art head-mounted display including the virtual replica of the real environment. After familiarization in quiet stance without and with VR, bipedal balance was perturbed by sinusoidal rotations of the visual scenery in the sagittal plane with an amplitude of 8° and a frequency of 0.2 Hz. Postural stability was quantified by mean center of mass speed derived from 3D-kinematics. A rmANOVA found increased postural instability only during the first perturbation cycle, i.e., the first 5 s. Succeeding the first perturbation cycle, visual afferents were downregulated to reduce the destabilizing influence of the sensory conflicts. In essence, only the transient beginning of sinusoidal oscillation alters balance compared to quiet standing. Therefore, continuous sinusoidal optic flow perturbations appear to be not suitable for balance training as they cannot trigger persisting sensory conflicts and hence challenge the postural system sustainably. Our study provides rationale for using unexpected and discrete optic flow perturbation paradigms to induce sustainable sensory conflicts.