Peroneal latency in normal and injured ankles at varying angles of perturbation

Peroneal reaction time delayed but dynamic single-legged stability retained in collegiate footballers during a simulated prolonged football protocol

Delayed peroneal reaction time and impaired single-legged dynamic stability were risk factors of lateral ankle sprain (LAS), yet no study explored the change of them during a football match. The aim is to explore the change of peroneal reaction time and single-legged dynamic stability during a football simulation protocol. Twelve collegiate football players voluntarily completed a 105-min football match simulation protocol in which peroneal reaction time, root-mean-square of mediolateral ground reaction force in first 0.4 s (RMS ML 0.4), and the mean mediolateral ground reaction force in the late stage (late dynamic MLGRF), were measured for both legs at 15-min intervals during the protocol. Peroneal reaction time was tested using an electromyography (EMG) system. The ground reaction force variables were measured from GRF data after a single-legged drop-jump landing. Repeated measures one-way MANOVA was conducted to evaluate variables over time and leg dominance. Statistical significance was set at p < 0.05 level. Peroneal reaction time significantly increased for both legs at 45 minutes and after 60 minutes. RMS ML 0.4 of both legs and late dynamic MLGRF for dominant leg remained unchanged throughout the protocol and late dynamic MLGRF for non-dominant leg significantly reduced at the 90th minute.

The influence of fatigue in evertor muscles during lateral ankle sprain

Ankle sprain in plantarflexion and inversion is one of the most common injuries occurring in daily activities and sports. Although acute symptoms may resolve quickly, many individuals have reported persistent pain and instability. Thus, understanding the factors that contribute to the occurrence of this type of injury is extremely important. Although sprains are multifactorial, a relationship can be established between sprain and fatigue. Therefore, the present study examined the latency and intensity of activation of the peroneus longus and brevis muscles under conditions of fatigue. Twenty-three women participated in the study, including 12 with functional instability of the ankle and 11 without a history of sprain. To induce fatigue, the volunteers maintained the force of eversion and plantarflexion at 70% of the maximum voluntary isometric contraction for as long as possible until a 10% decline in the rated force occurred. Ten simulations of ankle sprains were performed before and after fatigue at random for each side, with simultaneous recordings of the electromyographic signals, using a simulator platform for inversion sprain and plantarflexion. As a result, after fatigue, no change in latency was observed. However, a reduction in the intensity of contraction of the muscles analyzed in both groups was observed. Neuromuscular control was concluded to be compromised in situations of fatigue, while differences in muscle behavior were not observed between stable and unstable ankles.

Assessing Outcomes in People With Chronic Ankle Instability: The Ability of Functional Performance Tests to Measure Deficits in Physical Function and Perceived Instability

Study Design Laboratory-based, cross-sectional study. Background Functional performance tests (FPTs) assess short bouts of unilateral hops for either distance or speed. More research is needed to identify specific FPTs that may be useful for measuring asymmetry outcomes related to functional performance and perceived instability deficits in individuals with chronic ankle instability (CAI). Objectives To identify FPTs that are sensitive to subjective and objective deficits associated with CAI. Methods Twenty-four subjects with unilateral CAI (10 male, 14 female; mean ± SD age, 20.7 ± 3.0 years) and 24 healthy, matched controls (10 male, 14 female; age, 20.1 ± 2.6 years) completed 5 unilateral FPTs in random order. Mean FPT scores and functional symmetry percentages were calculated and compared between groups using 2 separate 1-way multivariate analyses of variance (MANOVAs). Perceived instability symmetry percentages were compared between groups using a Mann-Whitney U analysis. Results There were no differences in the mean FPT scores (P>.05) or functional symmetry percentages (P>.05) between groups for any of the 5 FPTs. However, participants with CAI perceived greater instability when using their involved limb during the side hop (P = .02), 6-meter crossover hop (P = .003), lateral hop (P = .007), and figure-of-eight hop (P = .008). Conclusion There were no differences in mean functional scores between groups for all 5 FPTs, and each group performed symmetrically. Regardless, administering a visual analog scale following the completion of the side hop, 6-meter crossover hop, lateral hop, and figure-of-eight hop tests captures subjective reports of perceived instability in the involved limb that can be compared bilaterally throughout treatment. J Orthop Sports Phys Ther 2018;48(5):372-380. Epub 30 Mar 2018. doi:10.2519/jospt.2018.7514.

Design and development of a five-bar robot for research into lower extremity proprioception

Ankle inversion is a common injury of musculoskeletal system among athletes and also in the older population. Investigation into ankle inversion requires quantitative assessment of the smallest amount of height/angle change in the floor that can be perceived by human. Blocks of different thickness have been used to change floor height manually during tests. We aimed to develop an automatic apparatus that is able to provide improved height and angle resolutions for dynamic ankle proprioception. We designed and manufactured a five-bar planar robot with one coupler serving as the mobile platform. We used a stiffening rib to achieve consistent differences in deflection across the workspace of the mobile platform. The reported robot translates at the maximal speed 423 mm/s with a resolution at 0.21 mm under a maximal load of 358 kg. This robot allows for increased sensitivity, which may lead to further investigation of functional proprioceptive ability and reflect finely tuned sensory requirements for upright stance.

Reaction Times and Electromechanical Delay in Reactions of Increasing and Decreasing Force

The purpose of this study was to compare reaction times and electromechanical delay between reactions to increase force from rest and reactions to decrease force from an active state in the quadriceps femoris of healthy young adults. Force, position, and electromyographic data were recorded from 35 subjects reacting to a forced knee-flexion perturbation. Electromechanical delay was assessed through cross-correlation of the filtered EMG and force data. Reaction time to increase force ( M = 159.9 msec., 95% CI = 149.9–169.9 msec.) was significantly longer than RT to decrease force ( M = 124.4 msec., 95% CI = 118.7–130.1 msec.). This difference was partially caused by a difference in electromechanical delay (RT to increase force electromechanical delay was 63 msec., 95% CI = 60–67 msec., greater than the RT to decrease force electromechanical delay of 49 msec., 95% CI = 46–52 msec.). This difference in reaction time could be important in identifying and interpreting physiologically meaningful changes in muscle force and in intermuscular coordination during movement.

Muscle Activation During Landing Before and After Fatigue in Individuals With or Without Chronic Ankle Instability

CONTEXT

Ankle instability is a common condition in physically active individuals. It often occurs during a jump landing or lateral motion, particularly when participants are fatigued.

OBJECTIVE

To compare muscle activation during a lateral hop prefatigue and postfatigue in individuals with or without chronic ankle instability (CAI).

DESIGN

Cross-sectional study.

SETTING

Sports medicine research laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 32 physically active participants volunteered for the study. Sixteen participants with CAI (8 men, 8 women; age = 20.50 ± 2.00 years, height = 172.25 ± 10.87 cm, mass = 69.13 ± 13.31 kg) were matched with 16 control participants without CAI (8 men, 8 women; age = 22.00 ± 3.30 years, height = 170.50 ± 9.94 cm, mass = 69.63 ± 14.82 kg) by age, height, mass, sex, and affected side.

INTERVENTION(S)

Electromyography of the tibialis anterior, peroneus longus, gluteus medius, and gluteus maximus was measured before and after a functional fatigue protocol.

MAIN OUTCOME MEASURE(S)

Activation of 4 lower extremity muscles was measured 200 milliseconds before and after landing from a lateral hop.

RESULTS

We observed no interactions. The group main effects for the peroneus longus demonstrated higher muscle activation in the CAI group (52.89% ± 11.36%) than in the control group (41.12% ± 11.36%) just before landing the lateral hop (F_1,30 = 8.58, P = .01), with a strong effect size (d = 1.01). The gluteus maximus also demonstrated higher muscle activation in the CAI group (45.55% ± 12.08%) than in the control group (36.81% ± 12.08%) just before landing the lateral hop (F_1,30 = 4.19, P = .049), with a moderate effect size (d = 0.71). We observed a main effect for fatigue for the tibialis anterior, with postfatigue activation higher than prefatigue activation (F_1,30 = 7.45, P = .01). No differences were present between groups for the gluteus medius.

CONCLUSIONS

Our results support the presence of a centralized feed-forward neuromuscular alteration in patients with CAI, not only in the ankle-joint muscles but also in the proximal hip muscles. These results may have implications for rehabilitation programs in these patients.

Feedback and Feedforward Control During Walking in Individuals With Chronic Ankle Instability

Study Design Controlled laboratory study. Background Recurrent ankle sprains associated with chronic ankle instability (CAI) occur not only in challenging sports but also in daily walking. Understanding whether and how CAI alters feedback and feedforward controls during walking may be important for developing interventions for CAI prevention or treatment. Objective To understand whether CAI is associated with changes in feedback and feedforward control when individuals with CAI are subjected to experimental perturbation during walking. Methods Twelve subjects with CAI and 12 control subjects walked on a treadmill while adapting to external loading that generated inversion perturbation at the ankle joint. Ankle kinematics around heel contact during and after the adaptation were compared between the 2 groups. Results Both healthy and CAI groups showed an increase in eversion around heel contact in early adaptation to the external loading. However, the CAI group adapted back toward the baseline, while the healthy controls showed further increase in eversion in late adaptation. When the external loading was removed in the postadaptation period, healthy controls showed an aftereffect consisting of an increase in eversion around heel contact, but the CAI group showed no aftereffect. Conclusion The results provide preliminary evidence that CAI may alter individuals' feedback and feedforward control during walking. J Orthop Sports Phys Ther 2016;46(9):775-783. Epub 5 Aug 2016. doi:10.2519/jospt.2016.6403.

The effect of repetitive ankle perturbations on muscle reaction time and muscle activity

The use of a tilt platform to simulate a lateral ankle sprain and record muscle reaction time is a well-established procedure. However, a potential caveat is that repetitive ankle perturbation may cause a natural attenuation of the reflex latency and amplitude. This is an important area to investigate as many researchers examine the effect of an intervention on muscle reaction time. Muscle reaction time, peak and average amplitude of the peroneus longus and tibialis anterior in response to a simulated lateral ankle sprain (combined inversion and plantar flexion movement) were calculated in twenty-two physically active participants. The 40 perturbations were divided into 4 even groups of 10 dominant limb perturbations. Within-participants repeated measures analysis of variance (ANOVA) tests were conducted to assess the effect of habituation over time for each variable. There was a significant reduction in the peroneus longus average amplitude between the aggregated first and last 10 consecutive ankle perturbations (F2.15,45.09=3.90, P=0.03, ɳp(2)=0.16). Authors should implement no more than a maximum of 30 consecutive ankle perturbations (inclusive of practice perturbations) in future protocols simulating a lateral ankle sprain in an effort to avoid significant attenuation of muscle activity.

Ankle muscle strength influence on muscle activation during dynamic and static ankle training modalities

Muscle weakness is considered a risk factor for ankle injury. Balance training and barefoot running have been used in an attempt to strengthen the muscles crossing the ankle. It is expected that training tasks that successfully strengthen the ankle would elicit increased muscular activity. However, it is unknown how an individual's ankle strength will influence the muscle activity used during a given task. Twenty-six participants performed dynamic (shod, barefoot running) and static tasks (squat on ground, squat on ®Bosu Ball) believed to strengthen the muscles surrounding the ankle. Electromyographic signals of the tibialis anterior, peroneus longus, gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) were recorded and analysed using a non-linearly scaled wavelet analysis. Participants were divided into a strong group and a weak group according to their isometric plantar-flexion torque. The weak group required more relative GL and GM muscle activity during each training task compared to the strong group. No difference was observed between shod and barefoot running. There was a significant effect of training task on muscle activation level for the weak group. Differences in ankle strength had a significant impact on muscle activation.

Neuromuscular control and rehabilitation of the unstable ankle

Lateral ankle sprain is a common orthopedic injury with a very high recurrence rate in athletes. After decades of research, it is still unclear what contributes to the high recurrence rate of ankle sprain, and what is the most effective intervention to reduce the incident of initial and recurrent injuries. In addition, clinicians often implement balance training as part of the rehabilitation protocol in hopes of enhancing the neuromuscular control and proprioception of the ankle joint. However, there is no consensus on whether the neuromuscular control and proprioception are compromised in unstable ankles. To reduce the prevalence of ankle sprains, the effectiveness of engaging balance training to enhance the neuromuscular control and proprioception of the ankle joint is also questionable.

Mechanism of camptocormia in Parkinson's disease analyzed by tilt table-EMG recording

BACKGROUND

We previously classified camptocormia of Parkinson's disease (PD) into upper and lower types based on the inflection point, and reported improvement of upper camptocormia after lidocaine injection into the external oblique. However, the exact pathophysiology of this phenomenon remains obscure.

METHODS

Surface electromyography (sEMG) was recorded in 11 PD patients with upper camptocormia, 11 PD patients with lower camptocormia, and 10 age-matched PD patients without postural deformity. Electrodes were positioned above the external oblique, hip flexors and paraspinal muscles at Th11 level bilaterally. Recording commenced with the patient in supine position on a tilt table, and continued when the table was tilted up to vertical position. Lidocaine was injected into the external oblique in patients with upper camptocormia and the psoas major in patients with lower camptocormia.

RESULTS

All patients with upper and lower camptocormia developed the corresponding camptocormic posture during tilt up. The onset of camptocormic posture was preceded by the appearance of sEMG activity in the external oblique in 10 out of 11 patients with upper camptocormia, but less frequently in patients with lower camptocormia and the controls. Hip flexors sEMG activity was recorded in almost all patients. Posture was improved in 8 out of 9 patients with upper camptocormia, and 9 out of 11 patients with lower camptocormia following injections of lidocaine.

CONCLUSIONS

The results suggest the external oblique is involved, at least in part, in the development of upper camptocormia. Although EMG findings cannot differentiate pathogenicity, the psoas major is probably involved in lower camptocormia.

Falls Associated with Muscle Strength in Patients with Knee Osteoarthritis and Self-reported Knee Instability

OBJECTIVE

We aimed to evaluate the associations between knee muscle strength (MS) and falls, controlling for knee joint proprioception, varus-valgus knee joint laxity, and knee pain, among patients with knee osteoarthritis (OA) reporting knee instability.

METHODS

A sample of 301 subjects (203 women, 98 men, 35-82 yrs) with established knee OA and self-reported knee instability was studied. The occurrence of at least 1 fall in the previous 3 months was assessed by questionnaire. Maximum knee extension and flexion strength were measured isokinetically. Additionally, proprioception, varus-valgus laxity, and pain were assessed. Student t tests were used to assess differences between subgroups. The association of muscle strength and falls was calculated using univariate and multivariate logistic regression analysis.

RESULTS

Over 10% of the subjects (31 out of 301) reported a fall in the previous 3 months. High knee extension muscle strength (crude OR 0.3, 95% CI 0.1-0.8, p = 0.022) and high knee flexion muscle strength (crude OR 0.2, 95% CI 0.0-1.0, p = 0.048) were associated with a lower risk of falls. Proprioception and laxity did not confound this relationship. After adjusting for pain, extensor strength had an adjusted OR of 0.5 (95% CI 0.2-1.4, p = 0.212) for falls and flexor strength had an adjusted OR of 0.4 (95% CI 0.1-2.3, p = 0.312).

CONCLUSION

High knee extension and flexion muscle strength decreased the risk of falls in patients with knee OA and self-reported knee instability. After considering the effect of pain, there was insufficient statistical power to detect an association between muscle strength and falls, which might be because of the low number of subjects who fell (n = 31).

Peroneal reaction time after ankle sprain: a systematic review and meta-analysis

BACKGROUND

Many studies have examined the temporal response of the peroneal muscles to sudden inversion perturbation in patients with a previous ankle sprain. The purpose of this systematic review with meta-analysis was to synthesize the evidence and determine whether peroneal reaction time (PRT) impairments are present after ankle sprain.

METHODS

An electronic search was conducted using PubMed Central and EBSCOhost (1965-January 2013). Articles were included if they 1) examined the PRT to sudden inversion perturbation in patients with a history of ankle sprain using a mechanical tilt platform, 2) made comparisons with a control group or contralateral limb with no history of ankle sprain, and 3) provided data for the calculation of effect sizes (ES). In addition to examining the overall effect of sustaining an ankle sprain on PRT, the effects of study design and subject characteristics on PRT were evaluated. Bias-corrected Hedges g ES and 95% confidence intervals (CI) were calculated to make comparisons across studies.

RESULTS

A total of 23 studies met the inclusion criteria. The overall ES was 0.67 (95% CI = 0.37-0.95, P < 0.001), indicating that a previous ankle sprain, regardless of study design or subject characteristics, resulted in moderate-to-strong PRT deficits. Further analyses determined studies with patients classified as having chronic ankle instability demonstrated large magnitude PRT deficits in between groups (ES = 0.72, 95% CI = 0.29-1.14, P = 0.001) and side-to-side (ES = 1.24, 95% CI = 0.70-1.79, P < 0.001) comparisons, whereas patients with all other ankle sprain histories demonstrated weak PRT alterations in between groups (ES = -0.21, 95% CI = -1.01 to 0.59, P = 0.61) and side-to-side (ES = 0.21, 95% CI = -0.19 to 0.60, P = 0.31) comparisons.

CONCLUSIONS

Overall, this meta-analysis determined that individuals with a previous ankle sprain exhibit delayed PRT. Further analyses determined that these deficits are more evident in patients with chronic ankle instability when compared with the contralateral uninvolved limb or a healthy control group.

Unloading reaction during sudden ankle inversion in healthy adults

The purpose of this research study was to determine the dynamics of early human response from sudden ankle inversion (30° tilt). Changes in vertical ground reaction forces (GRFs) following trapdoor release in a group of healthy subjects were compared to those from the similar experiments using a chair with two U shaped steel legs and matched weights of the human subjects. The experiments with the chair were further repeated with additional foam paddings at their bases to introduce visco-elastic properties to legs of the chair. Following the trapdoor release a decrease in the vertical ground reaction force under the inverting leg and subsequent increase in the supporting leg were observed in both human and chair experiments. The short onset of changes in vertical GRFs in our experiments indicate that the dynamic features of early response following trapdoor release are primarily due to mechanical events and may not be significantly affected by the neuromuscular reaction of human subjects.

[Neuromuscular deficits in chronic ankle instability. Frequency and significance - multicenter study]

The peroneal reaction time (PRT) is used in the assessment of neuromuscular deficits in chronic functional ankle instability. Powered by the Editorial Manager and Preprint Manager from Aries Systems Corporation the present study was conducted to determine the PRT in a large collective of patients with chronic ankle instability because it is unclear if this parameter of neuromuscular deficit is prolonged. In this study 186 patients underwent a diagnostic algorithm consisting of anamnesis, clinical examination, X-ray and determination of the PRT on a tilting platform. A prolonged PRT as a manifestation of a neuromuscular deficit could be detected in the majority of the patients (n = 143, 77%). Comparing the affected and healthy legs 77 patients (41%) showed a significant difference in talar shift (p = 0.002) and talar tilt (p = 0.04) in the radiological stress views. Of these 77 patients only 15 (8%) showed radiological evidence of a mechanical problem. As a consequence of recurring ankle sprains a post-traumatic deficit in proprioception has to be expected in most cases. In general a conservative therapy approach should be followed including specific training to improve neuromuscular and proprioceptive deficits.

Alterações neuromusculares no quadril associadas a entorses do tornozelo: revisão de literatura

INTRODUÇÃO: O tornozelo é a articulação mais frequentemente lesada na vida diária e nas atividades esportivas, sendo a entorse em inversão a lesão mais comum, com importantes repercussões funcionais e alto índice de recorrência após um evento de entorse primário. Os efeitos da lesão no tornozelo não se restringem a essa articulação, de modo que alterações na ativação e força da musculatura do quadril têm sido observadas após entorses em inversão do tornozelo. Essas alterações podem modificar o posicionamento do pé no instante do toque do calcanhar no solo, tornando o tornozelo mais suscetível à lesão por inversão. OBJETIVOS: O propósito deste estudo foi realizar uma revisão dos estudos da literatura que analisaram alterações neuromusculares presentes na articulação do quadril associadas a entorses em inversão do tornozelo. MATERIAIS E MÉTODOS: Foi realizada uma busca em bases eletrônicas (PubMed, MEDLINE, Cochrane, Web of Science, PEDro, SciELO, LILACS e Embase), do ano de 1966 até 2009, tendo sido encontrados 13 trabalhos considerados pertinentes ao tema. RESULTADOS: Desses estudos, nove observaram alterações de força e/ou recrutamento dos músculos do quadril após entorses do tornozelo, sugerindo-se que as consequências da lesão local manifestam-se também em estruturas proximais no membro inferior, com possível influência na ocorrência de recidivas. Apenas dois trabalhos foram análises prospectivas e não evidenciaram alterações neuromusculares no quadril antes da lesão do tornozelo, sugerindo-se que as alterações de força e/ou recrutamento dos músculos do quadril são provavelmente secundárias à lesão articular distal. CONCLUSÃO: Mais estudos, com maior uniformidade metodológica, são necessários para maior elucidação sobre a questão.

Influence of age, body mass index and leg dominance on functional ankle stability

BACKGROUND

The aim of this study was to examine the influence of age, body mass index (BMI) and leg dominance on the PRT, balance control and foot position sense.

MATERIALS AND METHODS

The proprioception of the ankle was investigated in 210 participants. All participants completed a questionnaire. The PRT was measured on a tilting platform. The position sense test was performed. Balance control was assessed with the Biodex Stability System (BSS), measuring the overall stability index (OSI) at the stable level 8 and the unstable level 2. Correlation analyses were performed between these data and age, BMI and leg dominance, using the Spearman-Rho coefficient with a two-sided significance level of p < 0.05.

RESULTS

Significant increases of the PRT and OSI in correlation to increased age and BMI were noted for both legs (p < 0.05). No positive correlation to age, BMI or leg dominance could be demonstrated for the foot position sense test. The PRT of the right leg was always significantly faster than that of the left leg, irrespective of leg dominance (p < 0.05). Surprisingly, individuals with a dominant right leg achieved better OSI scores in left single leg stance at the unstable level 2 (p < 0.05).

CONCLUSION

The PRT and the postural stability correlate with age and BMI, whereas the position sense test of the ankle does not. Furthermore, the PRT in right legs is always faster. This should be noted when functional ankle stability is evaluated in patients.

Neuromuscular control and ankle instability

Lateral ankle sprains (LAS) are common injuries in athletics and daily activity. Although most are resolved with conservative treatment, others develop chronic ankle instability (AI)-a condition associated with persistent pain, weakness, and instability-both mechanical (such as ligamentous laxity) and functional (neuromuscular impairment with or without mechanical laxity). The predominant theory in AI is one of articular deafferentation from the injury, affecting closed-loop (feedback/reflexive) neuromuscular control, but recent research has called that theory into question. A considerable amount of attention has been directed toward understanding the underlying causes of this pathology; however, little is known concerning the neuromuscular mechanisms behind the development of AI. The purpose of this review is to summarize the available literature on neuromuscular control in uninjured individuals and individuals with AI. Based on available research and reasonable speculation, it seems that open-loop (feedforward/anticipatory) neuromuscular control may be more important for the maintenance of dynamic joint stability than closed-loop control systems that rely primarily on proprioception. Therefore, incorporating perturbation activities into patient rehabilitation schemes may be of some benefit in enhancing these open-loop control mechanisms. Despite the amount of research conducted in this area, analysis of individuals with AI during dynamic conditions is limited. Future work should aim to evaluate dynamic perturbations in individuals with AI, as well as subjects who have a history of at least one LAS and never experienced recurrent symptoms. These potential findings may help elucidate some compensatory mechanisms, or more appropriate neuromuscular control strategies after an LAS event, thus laying the groundwork for future intervention studies that can attempt to reduce the incidence and severity of acute and chronic lateral ankle injury.

Reliability and discriminative validity of sudden ankle inversion measurements in patients with chronic ankle instability

BACKGROUND

Studies investigating peroneal muscle reaction times in chronically unstable ankle joints present conflicting results. The degree of reliability and accuracy of these measurements is unknown in patients with chronic ankle instability (CAI).

METHODS

40 patients with CAI and 30 healthy subjects were tested using a sudden ankle inversion of 50 degrees while standing on a trapdoor device. Sudden ankle inversion measurements were registered using electromyography, accelerometry and electrogoniometry. For reliability testing, intra-class coefficients (ICCs; model 3,1) and standard errors of measurements of the latency time, motor response time and electromechanical delay of the peroneus longus muscle, the time and angular position of onset of decelerations, the mean and maximum inversion speed and the total inversion time were calculated in 15 patients with CAI. To assess between-group differences, t-tests for independent samples (p<.05) were used.

RESULTS

ICCs ranged from .20 (angular position of onset of the second deceleration) to .98 (electromechanical delay of the peroneus longus muscle). Significant between-group differences were observed in only 2 of the 12 variables (for the electromechanical delay of the peroneus longus muscle, p=.001; time of onset of the second deceleration, p=.040).

CONCLUSIONS

The latency time and motor response time of the peroneus longus muscle, the total inversion time and the mean inversion speed demonstrate acceptable reliability in healthy subjects and patients. The latency time and motor response time of the peroneus longus muscle are not delayed in patients with CAI. Ankle inversion measurements are not discriminative for CAI.

Treatment of common deficits associated with chronic ankle instability

Lateral ankle sprains are amongst the most common injuries incurred by athletes, with the high rate of reoccurrence after initial injury becoming of great concern. Chronic ankle instability (CAI) refers to the development of repetitive ankle sprains and persistent residual symptoms post-injury. Some of the initial symptoms that occur in acute sprains may persist for at least 6 months post-injury in the absence of recurrent sprains, despite the athlete having returned to full functional activity. CAI is generally thought to be caused by mechanical instability (MI) or functional instability (FI), or both. Although previously discussed as separate entities, recent research has demonstrated that deficits associated with both MI and FI may co-exist to result in CAI. For clinicians, the main deficits associated with CAI include deficits in proprioception, neuromuscular control, strength and postural control. Based on the literature reviewed, it does seem that subjects with CAI have a deficit in frontal plane ankle joint positional sense. Subjects with CAI do not appear to exhibit any increased latency in the peroneal muscles in response to an external perturbation. Preliminary data suggest that feed-forward neuromuscular control may be more important than feed-back neuromuscular control and interventions are now required to address deficits in feed-forward neuromuscular control. Balance training protocols have consistently been shown to improve postural stability in subjects with CAI. Subjects with CAI do not experience decreased peroneus longus strength, but instead may experience strength deficits in the ankle joint invertor muscles. These findings are of great clinical significance in terms of understanding the mechanisms and deficits associated with CAI. An appreciation of these is vital to allow clinicians to develop effective prevention and treatment programmes in relation to CAI.

EVALUATION OF THE PROPRIOCEPTIVE INFLUENCE OF THE CUTANEOUS AFFERENTS TO THE ANKLE IN PATIENTS AFTER SURAL NERVE HARVESTING

OBJECTIVE

Cutaneous afferent nerves contribute to joint proprioception. The aim of this study was to retrospectively analyze the proprioceptive influence of the cutaneous afferents to the ankle in patients after sural nerve harvesting in comparison to controls.

METHODS

The proprioception of the ankle in 24 patients after sural nerve harvesting was investigated. The sural nerve was harvested bilaterally in Group 1 (n = 10), in the right leg in Group 2 (n = 6), and in the left leg in Group 3 (n = 8). The proprioception of the ankle was also tested in controls (Group 4, n = 24). The peroneal reaction time (PRT) was measured on a tilting platform. The position sense test was performed. Balance control was investigated with the Biodex Stability System (Biodex Medical Systems, Shirley, NY) at the stable Level 8 and unstable Level 2.

RESULTS

No significant differences among the groups were seen in the position sense test, the PRT, and all scores of the Biodex Stability System. The PRT showed significant differences in comparison to the contralateral leg for the peroneus brevis muscle in Group 1 (P = 0.005) and Group 4 (P = 0.001) as well as for the peroneus longus muscle in Group 3 (P = 0.036) and Group 4 (P = 0.001).

CONCLUSION

The proprioception of the ankle in patients after sural nerve harvesting is not reduced in comparison to controls. Significant differences of the PRT between the left and right legs are attributable to leg dominance in most cases and not to a loss of innervation. Harvesting of the sural nerve does not result in ankle instability.

Sensorimotor deficits with ankle sprains and chronic ankle instability

The presence of sensorimotor deficits in patients who have suffered ankle sprains or who have chronic ankle instability has been recognized for several decades; however, a body of research literature has developed that elucidates potential physiologic explanations for these deficits. Alterations in a spectrum of sensorimotor measures make it apparent that conscious perception of afferent somatosensory information, reflex responses, and efferent motor control deficits are present with ankle instability. The specific origin of these deficits local to the ankle ligaments or at the spinal or supraspinal levels of motor control have yet to be fully elucidated. It is clear, however, that both feedback and feedforward mechanisms of motor control are altered with ankle instability.

Ankle bracing, plantar-flexion angle, and ankle muscle latencies during inversion stress in healthy participants

CONTEXT

Ankle braces may enhance ankle joint proprioception, which in turn may affect reflexive ankle muscle activity during a perturbation. Despite the common occurrence of plantar-flexion inversion ankle injuries, authors of previous studies of ankle muscle latencies have focused on inversion stresses only.

OBJECTIVE

To examine the latency of the peroneus longus (PL), peroneus brevis (PB), and tibialis anterior (TA) muscles in response to various degrees of combined plantar-flexion and inversion stresses in braced and unbraced asymptomatic ankles.

DESIGN

Repeated measures.

SETTING

University biomechanics laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty-eight healthy females and 12 healthy males (n = 40: mean age = 23.63 years, range = 19 to 30 years; height = 172.75 +/- 7.96 cm; mass = 65.53 +/- 12.0 kg).

INTERVENTION(S)

Participants were tested under 2 conditions: wearing and not wearing an Active Ankle T1 brace while dropping from a custom-made platform into 10 degrees , 20 degrees , and 30 degrees of plantar flexion and 30 degrees of inversion.

MAIN OUTCOME MEASURE(S)

The time between platform drop and the onset of PL, PB, and TA electromyographic activity was measured to determine latencies. We calculated a series of 2-way analyses of variance to determine if latencies were different between the conditions (braced and unbraced) and among the plantar-flexion angles (alpha = .05).

RESULTS

No interaction was found between condition and plantar-flexion angle. No significant main effects were found for condition or plantar-flexion angle. Overall means for braced and unbraced conditions were not significantly different for each muscle tested. Overall means for angle for the PL, PB, and TA were not significantly different.

CONCLUSIONS

Reflexive activity of the PL, PB, or TA was unaffected by the amount of plantar flexion or by wearing an Active Ankle T1 brace during an unanticipated plantar-flexion inversion perturbation.

Modulation of Prelanding Lower-Limb Muscle Responses in Athletes with Multiple Ankle Sprains

PURPOSE

The objective of this study was to investigate modulation in prelanding muscle responses and its associated impact force on landing from unexpected and self-initiated drops in male basketball players with a history of bilateral multiple ankle sprains (BMAS).

METHODS

Prelanding EMG responses were recorded in four lower-limb muscles, together with the impact force on landing, while 20 healthy and 19 basketball players with BMAS performed unexpected, self-initiated drops from a height of 30 cm.

RESULTS

Group differences were detected after self-initiated but not unexpected drops. Two main changes in prelanding EMG responses were observed in the injured basketball players during the self-initiated drops. First, tibialis anterior (TA) was activated significantly earlier in the injured group, whereas left tensor fascia latae appeared closer to the moment of landing (P < 0.025) than in the healthy players. Second, cocontraction indexes between left TA and peroneus longus, and left TA and medial gastrocnemius, were significantly greater in the injured than in the healthy players (P < 0.025). On landing, higher magnitude-of-impact forces were observed in the injured players on the right leg (by 23%, P = 0.012).

CONCLUSION

In basketball players with BMAS, modulation of prelanding muscle response latencies occurred in injured (ankle) and uninjured (hip) joints during self-initiated but not unexpected drops. Greater cocontraction index between the left ankle muscle pairs in preparation for landing from self-initiated drops, and a significantly higher magnitude of impact force in the right leg on landing, were observed in the injured players.

The effect of fatigue and habituation on the stretch reflex of the ankle musculature

Many ankle injuries are said to occur when athletes are in a fatigued state; therefore, studies investigating the role that fatigue plays in ankle injuries are warranted. Furthermore, the contributions of the stretch reflex in countering the injury mechanism are still unclear. We hypothesized that (1) fatigue would impair the reflex response, (2) there would be no differences between genders, (3) habituation would be present, and (4) fatigue would exacerbate the effect of habituation. Forty healthy subjects participated and were divided into treatment and control groups. Stretch reflex measurements were taken for the tibialis anterior (TA), peroneus longus (PL), and peroneus brevis (PB) muscles in response to a rapid inversion perturbation. A fatigue intervention was administered to the treatment group, while the control group sat quietly. Post-test measurements were recorded within 5min and reflex latency (RL) and amplitude (RA) were calculated. RA decreased significantly, however a significant improvement was noted in RL in the PL and PB muscles. The effect that peripheral fatigue has on RL should not be considered a cause of ankle injuries. However, the diminished RA may suggest reduced dynamic stability after fatigue. Habituation was present and was exacerbated by fatigue, indicating that reflex testing is affected by fatigue and habituation, which must be taken into consideration in future studies.

Repeated ankle sprains and delayed neuromuscular response: acceleration time parameters

STUDY DESIGN

A comparative study.

OBJECTIVES

To assess whether in subjects with unilateral chronic ankle instability the dynamic reaction time of the affected ankle differs from the healthy ankle and from ankles of a control group.

BACKGROUND

Reaction time is an essential element in joint protection against sudden unexpected excessive movement requiring fast and coordinated muscle action. During a sudden ankle inversion movement, a reflex action of the evertor muscles is needed to counteract the movement. Adequate neuromuscular response is crucial and a delayed response could contribute to inversion trauma and subsequently to chronic ankle instability. The isokinetic dynamometer acceleration time (ACC-TIME) provides valuable information on dynamic neuromuscular ability.

MATERIAL AND METHODS

Patients with unilateral chronic ankle instability (n = 11) and healthy individuals in a control group (n = 11) were tested on an isokinetic dynamometer during 3 sets of 3 reciprocal inversion/eversion movements of both ankles at 30 degrees/s and 120 degrees/s. Analysis of variance models were used to compare the ACC-TIME of the affected ankle to the unaffected ankle of the same subjects and a control group.

RESULTS

For the evertor muscles at 30 degrees/s and 120 degrees/s a significantly prolonged ACC-TIME was found when comparing the affected ankles to the contralateral ankles and both ankles of the control group. For the invertor muscles at 120 degrees/s a significantly prolonged ACC-TIME was found when comparing the affected ankle to the unaffected ankles of patients and those of the control group.

CONCLUSIONS

Because the most important evertor muscles are innervated by the fibular nerve, the significantly prolonged ACC-TIME of the affected ankle is consistent with the finding of a lower motor nerve conduction velocity of the fibular nerve after inversion trauma. The results support the concept of a delayed neuromuscular response as an important factor in the etiology of chronic ankle instability.

Knee stabilization in patients with medial compartment knee osteoarthritis

OBJECTIVE

Individuals with medial knee osteoarthritis (OA) experience knee laxity and instability. Strategies aimed at muscle stabilization may influence the long-term integrity of the joint. This study sought to determine how individuals with medial knee OA respond to a rapid valgus knee movement, to investigate the relationship between muscle-stabilization strategies and knee instability.

METHODS

Twenty-one subjects with medial knee OA and genu varum and 19 control subjects were tested. Subjects stood with the test limb on a movable platform, comprising a plate that translated laterally to rapidly stress the knee's medial periarticular structures and create a potentially destabilizing sensation at the knee joint. Knee motion and muscle responses were recorded. Subjects rated the condition of their knee with a self-report questionnaire about knee instability during daily activities.

RESULTS

Prior to plate movement, the OA subjects demonstrated more medial muscle co-contraction than did controls (P = 0.014). Following plate movement, the OA subjects shifted less weight off the test limb (P = 0.013) and had greater medial co-contraction (P = 0.037). OA subjects without knee instability had higher co-contraction of the vastus medialis medial hamstrings than did those who reported having instability that affected their daily activities (P = 0.038). More knee stability correlated positively with higher co-contraction of the vastus medialis medial hamstrings prior to plate movement (r = 0.459, P = 0.042).

CONCLUSION

Individuals with medial knee OA attempt to stabilize the knee with greater co-contraction of the medial muscle in response to laxity that appears on the medial side of the joint only. This strategy presumably contributes to higher joint compression and could exacerbate joint destruction, and therefore needs to be altered to slow or stop the progression of the OA disease process.

Effect of peripheral afferent alteration of the lateral ankle ligaments on dynamic stability

BACKGROUND

The sensorimotor influence of the lateral ankle ligaments in muscle activation is unclear.

HYPOTHESIS

The lateral ankle ligaments have significant sensorimotor influence on muscle activation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Muscle-firing characteristics in response to a high-speed inversion perturbation and during gait were assessed in 13 normal subjects. Solutions (1.5% lidocaine or a placebo of saline) were injected bilaterally into the anterior talofibular and calcaneofibular ligaments (1.5 ml per ligament) to alter peripheral afferent influence. Subjects were again tested with the same protocol.

RESULTS

The protective response of the anterior tibialis and peroneal muscles during inversion perturbation and mean muscle activation amplitude decreased during running after both injections. After injection, no significant differences were seen for muscle reflex latencies, maximum amplitude, time to maximum amplitude during inversion perturbation, or mean amplitude during walking.

CONCLUSION

The lateral ankle ligaments have a sensorimotor influence on muscle activation.

CLINICAL RELEVANCE

Induced edema from the injected solutions may have altered the sensorimotor influence of the lateral ankle ligaments, thereby inhibiting the dynamic ankle stabilizers. This finding suggests that dynamic stability may be compromised because of swelling after joint injury.

Trunk muscle onset detection technique for EMG signals with ECG artefact

The timing of trunk muscle activation has become an important element in the understanding of human movement in normal and chronic low back pain populations. The detection of anticipatory postural adjustment via trunk muscle onsets from electromyographic (EMG) signals can be problematic due to baseline noise or electro-cardiac (ECG) artefact. Shewhart protocols or whole signal analyses may show different degrees of sensitivity under different conditions. Muscle activity onsets were determined from surface EMG of seven muscles for five trials before and after fatigue were examined in four subjects (n=280). The objective of this study was to examine two detection methods (Shewhart and integrated protocol (IP)) in determining the onsets of trunk muscles. The variability of the baseline amplitude and the impact of added Gaussian noise on the detected onsets were used to test for robustness. The results of this study demonstrate that before and after fatigue there is a large degree of baseline variance in the trunk muscles (coefficients of variation between 40-65%) between trials. This could be normal response to body sway. The IP method was less susceptible to false onsets (detecting onsets in the baseline window) 3 vs. 51%. The findings suggest the IP method is robust with large variance in the baseline if the signal to noise ratio is greater than six. In spite of the robustness of the algorithm, the findings would suggest that statistical assessments should be used to target trials for selective visual inspection for subtle trunk muscle onsets.

Electromechanical assessment of ankle stability

The goal of this study was to approach ankle instability by measuring the electromechanical delay of the peroneal muscles (foot pronators). For that purpose, supramaximal electrical stimulation of common peroneal nerve was applied when the subject was standing on a force plate in bipedal stance or monopedal stance, postures requiring greater ankle stabilization. The electromechanical delay (EMD) was defined as the time interval between the onset of the peroneus longus (PL) electromyogram detected by surface electrodes and the onset of the lateral ground reaction force (Fy) measured on a force plate. Ten healthy subjects (control group, C-G) and ten subjects with functional ankle instability ("FAI" group, FAI-G) performed the tests. In C-G, the mean EMD values decreased significantly ( P<0.001) from the bipedal [10.54 (0.71) ms; mean (SD)] to the monopedal stance [8.67 (0.63 ms)]. Since a monopedal stance is known to require higher leg muscle tone resulting in a higher ankle stiffness, these results indicate that PL EMDs are sensitive to musculo-tendinous stiffness. They validate the choice of a PL EMD measurement as an indirect index of musculo-tendinous stiffness at the ankle. In both bipedal and monopedal stance conditions, EMD values were significantly higher in FAI subjects. They ranged from 12.64 (1.14) ms in the bipedal stance to 10.85 (1.07) ms in the monopedal stance. This suggests a lower musculo-tendinous stiffness at the ankle, which may contribute to the ankle instability.

Control of acceleration during sudden ankle supination in people with unstable ankles

STUDY DESIGN

Comparative study of differences in functional control during ankle supination in the standing position in matched stable and unstable ankles (ex post facto design).

OBJECTIVES

To document acceleration and deceleration during ankle supination in the standing position and to determine differences in control of supination perturbation between stable and unstable ankles.

BACKGROUND

Repetitive ankle sprain can be explained by mechanical instability only in a minority of cases. Exercise therapy for ankle instability is based on clinical experience. Joint stability has not yet been measured in dynamic situations that are similar to the situations leading to a traumatic sprain. The process of motor control during accelerating ankle supination has not been adequately addressed in the literature.

METHODS AND MEASURES

Patients with complaints of ankle instability (16 unstable ankles) and nonimpaired controls (18 stable ankles) were examined (N = 17 subjects, 10 women and 7 men). The average age was 23.7 +/- 5.0 years (range, 20-41 y). Control of supination speed was studied during 50 degrees of ankle supination in the standing position using accelerometry (total supination time and deceleration times) and electromyography (latency time). Timing of motor response was estimated by measuring electromechanical delay.

RESULTS

The presence of an early, sudden, and presumably passive slowdown of ankle supination in the standing position was observed. Peroneal muscle motor response was detected before the end of the supination. Unstable ankles showed significantly shorter total supination time (109.3 ms versus 124.1 ms) and significantly longer latency time (58.9 ms versus 47.7 ms).

CONCLUSIONS

Functional control in unstable ankles is less efficient in decelerating the ankle during the supination test procedures used in our study. Our conclusions are based on significantly faster total supination and significantly slower electromyogram response in unstable ankles. The results support the hypothesis that both decelerating the total supination movement during balance disturbance and enhancing the speed of evertor activation through exercise can be specific therapy goals.