Time to stabilization of anterior cruciate ligament-reconstructed versus healthy knees in National Collegiate Athletic Association Division I female athletes

Context:

Jump landing is a common activity in collegiate activities, such as women''s basketball, volleyball, and soccer, and is a common mechanism for anterior cruciate ligament (ACL) injury. It is important to better understand how athletes returning to competition after ACL reconstruction are able to maintain dynamic postural control during a jump landing.

Objective:

To use time to stabilization (TTS) to measure differences in dynamic postural control during jump landing in ACL-reconstructed (ACLR) knees compared with healthy knees among National Collegiate Athletic Association Division I female athletes.

Design:

Case-control study.

Setting:

University athletic training research laboratory.

Patients or Other Participants:

Twenty-four Division I female basketball, volleyball, and soccer players volunteered and were assigned to the healthy control group (n  =  12) or the ACLR knee group (n  =  12). Participants with ACLR knees were matched to participants with healthy knees by sport and by similar age, height, and mass.

Intervention(s):

At 1 session, participants performed a single-leg landing task for both limbs. They were instructed to stabilize as quickly as possible in a single-limb stance and remain as motionless as possible for 10 seconds.

Main Outcome Measure(s):

The anterior-posterior TTS and medial-lateral TTS ground reaction force data were used to calculate resultant vector of the TTS (RVTTS) during a jump landing. A 1-way analysis of variance was used to determine group differences on RVTTS. The means and SDs from the participants'' 10 trials in each leg were used for the analyses.

Results:

The ACLR group (2.01 ± 0.15 seconds, 95% confidence interval [CI]  =  1.91, 2.10) took longer to stabilize than the control group (1.90 ± 0.07 seconds, 95% CI  =  1.86, 1.95) (F_1,22  =  4.28, P  =  .05). This result was associated with a large effect size and a 95% CI that did not cross zero (Cohen d  =  1.0, 95% CI  =  0.91, 1.09).

Conclusions:

Although they were Division I female athletes at an average of 2.5 years after ACL reconstruction, participants with ACLR knees demonstrated dynamic postural-control deficits as evidenced by their difficulty in controlling ground reaction forces. This increased TTS measurement might contribute to the established literature reflecting differences in single-limb dynamic control. Clinicians might need to focus rehabilitation efforts on stabilization after jump landing. Further research is needed to determine if TTS is a contributing factor in future injury.     

Submaximal Force Steadiness and Accuracy in Patients With Chronic Ankle Instability

ContextPatients with chronic ankle instability (CAI) have demonstrated sensorimotor impairments. Submaximal force steadiness and accuracy measure sensory, motor, and visual function via a feedback mechanism, which helps researchers and clinicians comprehend the sensorimotor deficits associated with CAI.ObjectiveTo determine if participants with CAI experienced deficits in hip and ankle submaximal force steadiness and accuracy compared with healthy control participants.DesignCase-control study.SettingResearch laboratory.Patients or Other ParticipantsTwenty-one patients with CAI and 21 uninjured individuals.Main Outcome Measure(s)Maximal voluntary isometric contraction (MVIC) and force steadiness and accuracy (10% and 30% of MVIC) of the ankle evertors and invertors and hip abductors were assessed using the central 10 seconds (20%–87% of the total time) of the 3 trials.ResultsRelative to the control group, the CAI group demonstrated less accuracy of the invertors (P < .001). Across all motions, the CAI group showed less steadiness (P < .001) and less accuracy (P < .01) than the control group at 10% of MVIC. For MVIC, the CAI group displayed less force output in hip abduction than the uninjured group (P < .0001).ConclusionsPatients with CAI were unable to control ongoing fine force (10% and 30% of MVIC) through a feedback mechanism during an active test. These findings suggested that deficits in sensorimotor control predisposed patients with CAI to injury positions because they had difficulty integrating the peripheral information and correcting their movements in relation to visual information.     

Alterations in Neuromuscular Control at the Knee in Individuals With Chronic Ankle Instability

Context:

Few authors have assessed neuromuscular knee-stabilization strategies in individuals with chronic ankle instability (CAI) during functional activities.

Objective:

To investigate the influence of CAI on neuromuscular characteristics around the knee during a stop-jump task.

Design:

Case-control study.

Setting:

Research laboratory.

Participants or Other Participants:

A total of 19 participants with self-reported unilateral CAI and 19 healthy control participants volunteered for this study.

Intervention(s):

Participants performed double-legged, vertical stop-jump tasks onto a force plate, and we measured muscle activation around the knee of each limb.

Main Outcome Measure(s):

We calculated the integrated electromyography for the vastus medialis oblique, vastus lateralis, medial hamstrings, and lateral hamstrings muscles during the 100 ms before and after initial foot contacts with the force plate and normalized by the ensemble peak electromyographic value. Knee sagittal-plane kinematics were also analyzed during a stop-jump task.

Results:

Compared with control participants, the CAI group demonstrated greater prelanding integrated electromyographic activity of the vastus medialis oblique (CAI = 52.28 ± 11.25%·ms, control = 43.90 ± 10.13%·ms, t₃₆ = 2.41, P = .021, effect size = 0.78, 95% confidence interval = 0.11, 1.43) and less knee-flexion angle at the point of initial foot contact (CAI = 7.81° ± 8.27°, control = 14.09° ± 8.7°, t₃₆ = −2.28, P = .029, effect size = −0.74, 95% confidence interval = −1.38, −0.07) and at 100 ms post–initial foot contact (CAI = 51.36° ± 5.29°, control = 58.66° ± 7.66°, t₃₆ = −3.42, P = .002, effect size = −1.11, 95% confidence interval = −1.77, −0.40). No significant results were noted for the other electromyographic measures.

Conclusions:

We found altered feed-forward patterns of the vastus medialis oblique and altered postlanding knee sagittal-plane kinematics in the CAI group. These observations may provide insight regarding sensorimotor characteristics that may be associated with CAI.Key Words: feed-forward pattern, feedback, sensorimotor control

Key Points

• Increased preparatory vastus medialis oblique muscle activation and decreased postlanding knee-flexion angle were seen in participants with chronic ankle instability compared with the control group during a vertical stop jump.
• Feed-forward sensorimotor control around the knee should be addressed during therapeutic interventions for chronic ankle instability.

Chronic ankle instability (CAI) is common after an acute lateral ankle sprain (LAS) in physically active individuals,^1–3 leading to self-assessed disability and decreased quality of life.⁴ It has been reported that CAI is a leading factor for the development of posttraumatic osteoarthritis in the ankle,^1,5 requiring costly medical diagnostic techniques and extensive treatments. With a high rate of recurrence plus the complications of prolonged functional impairments after ankle sprains, there is an increased need for evidence-based practice to develop and implement more effective intervention programs for CAI.One important step in reducing the recurrence rate is to understand the underlying sensorimotor mechanisms for CAI. After LAS, altered afferent inputs from the somatosensory system around the ankle and central changes in sensorimotor control may result in proximal joint adaptations to compensate for residual symptoms and functional impairments.^6–13 Previous researchers^6,10 have indirectly assessed sensorimotor control strategies in CAI patients at the knee using sagittal-plane kinematics. Gribble and Robinson⁶ found greater knee extension before and at the point of ground impact⁷ during a vertical jump-landing task, whereas Caulfield and Garrett¹⁰ observed greater knee flexion before and after landing during a drop-jump task. These contradictory findings may be attributable to differences between these studies in the demands of the jump-landing tasks; however, neither group quantified electromyography (EMG) of the knee musculature during the landing tasks. Thus, we still do not know how activation of the knee flexors and extensors influences sagittal-plane kinematics during jump-landing tasks in individuals with a history of ankle injury.Although several EMG investigations have demonstrated altered preparatory muscle-activation patterns in the ankle during jump landings in CAI patients,^9,11–14 few investigators have examined preparatory EMG measures in the knee during a dynamic task within this population, which may limit our estimation of relative preparatory activity of muscles in the knee. Delahunt et al¹¹ observed an increase in rectus femoris activation before ground impact during a lateral-hop task in individuals with CAI, supporting modified preprogrammed muscle-activation patterns via feed-forward motor control to prepare for ground impact. Additionally, Delahunt et al¹⁴ reported that those with CAI exhibited no differences in preparatory rectus femoris muscle activation during a drop-landing task. However, a drop-jump task is not a sport-related functional task and does not necessarily replicate the potential mechanism of injury.Whereas a relationship between CAI and altered biomechanical patterns at the knee has been established, few authors have quantitatively assessed sensorimotor control strategies at the knee using EMG while measuring sagittal-plane kinematics in individuals with CAI during other high-risk and sport-related functional activities, such as a vertical stop jump. It is important to examine knee muscle activation and sagittal-plane kinematic patterns to determine the potential effect of CAI on the sensorimotor control mechanism, especially pre-event decisions and postevent reactions, during a stop-jump maneuver. Researchers^6,10 have speculated that adapted feed-forward sensorimotor control strategies at the knee associated with CAI could be a way to protect the unstable ankle by controlling the position of the ankle and center of mass on ground impact. However, a diminished level of dynamic stability and energy dissipation of the knee musculature after landing has been observed in individuals with CAI.^6,7,15 Therefore, this proposed protective response to the unstable ankle may not be an efficient response. Although information is limited, there is a potential link between a history of ankle sprain and risk of injury at the knee joint.^16–18 The potential sensorimotor adaptations associated with CAI may not necessarily be protective for other joints. Identifying an underlying relationship between CAI and compensatory sensorimotor control in the knee may help clinicians and researchers to develop more comprehensive interventions to enhance global coordination in those with CAI and prevent future injury. Thus, the purpose of our study was to examine individuals with and without unilateral CAI for the presence of altered neuromuscular control in the knee during a vertical stop jump. Previous investigators observed a smaller knee-flexion angle before and after ground impact during a jump-landing task in participants with CAI compared with healthy controls.^6,7,19 Furthermore, increased preparatory muscle activation in the ankle during a stop-jump task has been reported in those with CAI.¹² Our hypotheses were that, during a stop-jump task, participants with CAI would demonstrate (1) increased quadriceps muscle activation before and after landing; (2) increased hamstrings muscle activation before landing; (3) decreased hamstrings muscle activation after landing; and (4) reduced knee-flexion angle before and after landing, as compared with participants without CAI.     

The Effects of Fatigue and Chronic Ankle Instability on Dynamic Postural Control

OBJECTIVE: Deficits in static postural control related to chronic ankle instability (CAI) and fatigue have been investigated separately, but little evidence links these factors to performance of dynamic postural control. Our purpose was to investigate the effects of fatigue and CAI on performance measures of a dynamic postural-control task, the Star Excursion Balance Test. DESIGN AND SETTING: For each of the 3 designated reaching directions, 4 separate 5 (condition) x 2 (time) x 2 (side) analyses of variance with a between factor of group (CAI, healthy) were calculated for normalized reach distance and maximal ankle-dorsiflexion, knee-flexion, and hip-flexion angles. All data were collected in the Athletic Training Research Laboratory. SUBJECTS: Thirty subjects (16 healthy, 14 CAI) participated. MEASUREMENTS: All subjects completed 5 testing sessions, during which sagittal-plane kinematics and reaching distances were recorded while they performed 3 reaching directions (anterior, medial, and posterior) of the Star Excursion Balance Test, with the same stance leg before and after different fatiguing conditions. The procedure was repeated for both legs during each session. RESULTS: The involved side of the CAI subjects displayed significantly smaller reach distance values and knee-flexion angles for all 3 reaching directions compared with the uninjured side and the healthy group. The effects of fatigue amplified this trend. CONCLUSIONS: Chronic ankle instability and fatigue disrupted dynamic postural control, most notably by altering control of sagittal-plane joint angles proximal to the ankle.     

Gait Kinematics After Taping in Participants With Chronic Ankle Instability

Context:

Chronic ankle instability is characterized by repetitive lateral ankle sprains. Prophylactic ankle taping is a common intervention used to reduce the risk of ankle sprains. However, little research has been conducted to evaluate the effect ankle taping has on gait kinematics.

Objective:

To investigate the effect of taping on ankle and knee kinematics during walking and jogging in participants with chronic ankle instability.

Design:

Controlled laboratory study.

Setting:

Motion analysis laboratory.

Patients or Participants:

A total of 15 individuals (8 men, 7 women; age = 26.9 ± 6.8 years, height = 171.7 ± 6.3 cm, mass = 73.5 ± 10.7 kg) with self-reported chronic ankle instability volunteered. They had an average of 5.3 ± 3.1 incidences of ankle sprain.

Intervention(s):

Participants walked and jogged in shoes on a treadmill while untaped and taped. The tape technique was a traditional preventive taping procedure. Conditions were randomized.

Main Outcome Measure(s):

Frontal-plane and sagittal-plane ankle and sagittal-plane knee kinematics were recorded throughout the entire gait cycle. Group means and 90% confidence intervals were calculated, plotted, and inspected for percentages of the gait cycle in which the confidence intervals did not overlap.

Results:

During walking, participants were less plantar flexed from 64% to 69% of the gait cycle (mean difference = 5.73° ± 0.54°) and less inverted from 51% to 61% (mean difference = 4.34° ± 0.65°) and 76% to 81% (mean difference = 5.55° ± 0.54°) of the gait cycle when taped. During jogging, participants were less dorsiflexed from 12% to 21% (mean difference = 4.91° ± 0.18°) and less inverted from 47% to 58% (mean difference = 6.52° ± 0.12°) of the gait cycle when taped. No sagittal-plane knee kinematic differences were found.

Conclusions:

In those with chronic ankle instability, taping resulted in a more neutral ankle position during walking and jogging in shoes on a treadmill. This change in foot positioning and the mechanical properties of the tape may explain the protective aspect of taping in preventing lateral ankle sprains.Key Words: external ankle supports, ankle prophylactic measures, recurrent ankle sprains

Key Points

• Taping the ankles of participants with chronic ankle instability resulted in more neutral positioning when they walked or jogged in shoes on a treadmill.
• Taping may protect the ankle by way of its mechanical properties and its neuromuscular effect on ankle position.

Lateral ankle sprains are very common injuries,¹ comprising an estimated 85% of all ankle injuries.^2,3 A history of ankle sprain has been found to be the leading risk factor in predicting future sprains.^4–6 Up to an estimated 70% of individuals who incur an initial ankle sprain and who are exposed to sports with a high risk of ankle-joint injuries will develop chronic ankle instability (CAI),^7,8 which is characterized by residual symptoms for at least 1 year after the initial ankle sprain.^8–10 Although the high prevalence of CAI is known, very little is actually understood regarding the mechanism or prevention of lateral ankle sprains.Gait kinematic alterations in those with a history of lateral ankle sprain have been hypothesized to contribute to CAI.^11–13 In a cadaver study¹⁴ of foot–floor clearance, inverting the foot 10°, regardless of plantar flexion, caused a collision between the lateral aspect of the foot and the floor, resulting in an ankle sprain. Individuals with CAI underestimate the combined motions of plantar flexion and inversion during passive joint position sense testing.¹⁵ These alterations in joint position sense may lead to alterations in kinematics during gait, which may contribute to ankle sprains and instability; an increased plantar-flexion touch-down position upon initial contact is known to increase the risk of ankle-joint injury.^14,16 Recently, researchers have compared the ankle kinematics of CAI participants with healthy controls while walking and jogging on a treadmill barefoot^17,18 and shod¹⁹ and walking on a walkway while shod.²⁰ Compared with healthy controls, frontal-plane and sagittal-plane kinematics were altered during various aspects of the gait cycle, and these changes are believed to contribute to repetitive incidences of ankle sprains.Prophylactic ankle taping is a common means of reducing the risk of injury to the lateral ankle ligaments, including recurrent ankle sprains.^21,22 The purpose of ankle taping is to restrict ankle inversion and plantar-flexion motion.^22,23 In healthy people, taping reduces sagittal-plane range of motion compared with the untaped condition while running, cutting, and landing from a drop.^24–26 Sagittal-plane kinematics during walking have been reported to be altered at foot contact and toe-off in individuals with CAI wearing an ankle brace.²⁷ During a functional drop landing, those with CAI demonstrated a decreased plantar-flexion angle immediately (50 milliseconds) before and at initial contact while wearing prophylactic ankle-joint taping compared with the untaped condition.²⁸ Previous researchers, however, have focused on discrete time points²⁷ or a specific window²⁸ during the gait cycle. We know of no literature evaluating frontal-plane and sagittal-plane kinematics during the entire walking and jogging gait cycle when CAI participants were taped.Therefore, the purpose of our study was to compare frontal-plane and sagittal-plane ankle kinematics in shod CAI participants while walking and jogging on a treadmill with or without traditional ankle taping. The secondary purpose was to evaluate sagittal-plane knee kinematics to determine if changes occurred with ankle taping. We evaluated kinematics at the knee to determine if kinematic alterations at the ankle affected movement up the kinetic chain.     

Association of Quadriceps and Hamstrings Cocontraction Patterns With Knee Joint Loading

Context:

Sex differences in neuromuscular control of the lower extremity have been identified as a potential cause for the greater incidence of anterior cruciate ligament (ACL) injuries in female athletes compared with male athletes. Women tend to land in greater knee valgus with higher abduction loads than men. Because knee abduction loads increase ACL strain, the inability to minimize these loads may lead to ACL failure.

Objective:

To investigate the activation patterns of the quadriceps and hamstrings muscles with respect to the peak knee abduction moment.

Design:

Cross-sectional study.

Setting:

Neuromuscular research laboratory.

Patients or Other Participants:

Twenty-one recreationally active adults (11 women, 10 men).

Main Outcome Measure(s):

Volunteers performed 3 trials of a 100-cm forward hop. During the hop task, we recorded surface electromyographic data from the medial and lateral hamstrings and quadriceps and recorded lower extremity kinematics and kinetics. Lateral and medial quadriceps-to-hamstrings (Q∶H) cocontraction indices, the ratio of medial-to-lateral Q∶H cocontraction, normalized root mean square electromyographic data for medial and lateral quadriceps and hamstrings, and peak knee abduction moment were calculated and used in data analyses.

Results:

Overall cocontraction was lower in women than in men, whereas activation was lower in the medial than in the lateral musculature in both sexes (P < .05). The medial Q∶H cocontraction index (R²  =  0.792) accounted for a significant portion of the variance in the peak knee abduction moment in women (P  =  .001). Women demonstrated less activation in the vastus medialis than in the vastus lateralis (P  =  .49) and less activation in the medial hamstrings than in the lateral hamstrings (P  =  .01).

Conclusions:

Medial-to-lateral Q∶H cocontraction appears to be unbalanced in women, which may limit their ability to resist abduction loads. Because higher abduction loads increase strain on the ACL, restoring medial-to-lateral Q∶H cocontraction balance in women may help reduce ACL injury risk.     

Ankle bracing, fatigue, and time to stabilization in collegiate volleyball athletes

CONTEXT: Fatigue has been shown to disrupt dynamic stability in healthy volunteers. It is not known if wearing prophylactic ankle supports can improve dynamic stability in fatigued athletes. OBJECTIVE: To determine the type of ankle brace that may be more effective at providing dynamic stability after a jump-landing task during normal and fatigued conditions. DESIGN: Two separate repeated-measures analyses of variance with 2 within-subjects factors (condition and time) were performed for each dependent variable. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten healthy female collegiate volleyball athletes participated (age = 19.5 +/- 1.27 years, height = 179.07 +/- 7.6 cm, mass = 69.86 +/- 5.42 kg). INTERVENTION(S): Athletes participated in 3 separate testing sessions, applying a different bracing condition at each session: no brace (NB), Swede-O Universal lace-up ankle brace (AB), and Active Ankle brace (AA). Three trials of a jump-landing task were performed under each condition before and after induced functional fatigue. The jump-landing task consisted of a single-leg landing onto a force plate from a height equivalent to 50% of each participant's maximal jump height and from a starting position 70 cm from the center of the force plate. MAIN OUTCOME MEASURE(S): Time to stabilization in the anterior-posterior (APTTS) and medial-lateral (MLTTS) directions. RESULTS: For APTTS, a condition-by-time interaction existed (F(2,18) = 5.55, P = .013). For the AA condition, Tukey post hoc testing revealed faster pretest (2.734 +/- 0.331 seconds) APTTS than posttest (3.817 +/- 0.263 seconds). Post hoc testing also revealed that the AB condition provided faster APTTS (2.492 +/- 0.271 seconds) than AA (3.817 +/- 0.263 seconds) and NB (3.341 +/- 0.339 seconds) conditions during posttesting. No statistically significant findings were associated with MLTTS. CONCLUSIONS: Fatigue increased APTTS for the AA condition. Because the AB condition was more effective than the other 2 conditions during the posttesting, the AB appears to be the best option for providing dynamic stability in the anterior-posterior direction during a landing task.     

Dynamic Stabilization Time After Isokinetic and Functional Fatigue

OBJECTIVE: To compare the effects of an isokinetic fatigue protocol and a functional fatigue protocol on time to stabilization (TTS), ground reaction force (GRF), and joint kinematics during a jump landing. DESIGN AND SETTING: Subjects were assessed on 2 occasions for TTS, GRF, and joint kinematics immediately before and after completing a fatigue protocol. One week separated the 2 sessions, and the order of fatigue protocols was randomly assigned and counterbalanced. SUBJECTS: Twenty healthy male (n = 8, age = 21.8 +/- 1.4 years, height = 180.6 +/- 7.6 cm, and mass = 74.1 +/- 13.0 kg) and female (n = 12, age = 22.2 +/- 2.1 years, height = 169.3 +/- 9.8 cm, and mass = 62.5 +/- 10.1 kg) subjects volunteered to participate. MEASUREMENTS: Subjects performed 2-legged jumps equivalent to 50% of maximum jump height, followed by a single-leg landing onto the center of a forceplate 70 cm from the starting position. Peak vertical GRF and vertical, medial-lateral, and anterior-posterior TTS were obtained from forceplate recordings. Maximum ankle dorsiflexion, knee-flexion, and knee-valgum angles were determined using 3-dimensional motion analysis. RESULTS: A 2-way analysis of variance with repeated measures revealed no significant differences when comparing TTS, GRF, and joint kinematics after isokinetic and functional fatigue protocols. CONCLUSIONS: No difference was noted between isokinetic and functional fatigue protocols relative to dynamic stability when landing from a jump.     

Customized Noise-Stimulation Intensity for Bipedal Stability and Unipedal Balance Deficits Associated With Functional Ankle Instability

Context:

Stochastic resonance stimulation (SRS) administered at an optimal intensity could maximize the effects of treatment on balance.

Objective:

To determine if a customized optimal SRS intensity is better than a traditional SRS protocol (applying the same percentage sensory threshold intensity for all participants) for improving double- and single-legged balance in participants with or without functional ankle instability (FAI).

Design:

Case-control study with an embedded crossover design.

Setting:

Laboratory.

Patients or Other Participants:

Twelve healthy participants (6 men, 6 women; age = 22 ± 2 years, height = 170 ± 7 cm, mass = 64 ± 10 kg) and 12 participants (6 men, 6 women; age = 23 ± 3 years, height = 174 ± 8 cm, mass = 69 ± 10 kg) with FAI.

Intervention(s):

The SRS optimal intensity level was determined by finding the intensity from 4 experimental intensities at the percentage sensory threshold (25% [SRS₂₅], 50% [SRS₅₀], 75% [SRS₇₅], 90% [SRS₉₀]) that produced the greatest improvement in resultant center-of-pressure velocity (R-COPV) over a control condition (SRS₀) during double-legged balance. We examined double- and single-legged balance tests, comparing optimal SRS (SRS_opt1) and SRS₀ using a battery of center-of-pressure measures in the frontal and sagittal planes.

Main Outcome Measure(s):

Anterior-posterior (A-P) and medial-lateral (M-L) center-of-pressure velocity (COPV) and center-of-pressure excursion (COPE), R-COPV, and 95th percentile center-of-pressure area ellipse (COPA-95).

Results:

Data were organized into bins that represented optimal (SRS_opt1), second (SRS_opt2), third (SRS_opt3), and fourth (SRS_opt4) improvement over SRS₀. The SRS_opt1 enhanced R-COPV (P ≤ .05) over SRS₀ and other SRS conditions (SRS₀ = 0.94 ± 0.32 cm/s, SRS_opt1 = 0.80 ± 0.19 cm/s, SRS_opt2 = 0.88 ± 0.24 cm/s, SRS_opt3 = 0.94 ± 0.25 cm/s, SRS_opt4 = 1.00 ± 0.28 cm/s). However, SRS did not improve R-COPV over SRS₀ when data were categorized by sensory threshold. Furthermore, SRS_opt1 improved double-legged balance over SRS₀ from 11% to 25% in all participants for the center-of-pressure frontal- and sagittal-plane assessments (P ≤ .05). The SRS_opt1 also improved single-legged balance over SRS₀ from 10% to 17% in participants with FAI for the center-of-pressure frontal- and sagittal-plane assessments (P ≤ .05). The SRS_opt1 did not improve single-legged balance in participants with stable ankles.

Conclusions:

The SRS_opt1 improved double-legged balance and transfers to enhancing single-legged balance deficits associated with FAI.Key Words: chronic ankle instability, noise, postural stability, therapy

Key Points

• Stochastic resonance stimulation can be considered an alternative treatment for balance impairments.
• Stochastic resonance stimulation may be an effective treatment in the early stages of rehabilitation to facilitate immediate balance improvements that may help patients transition to complex postural stability exercises or functional movements.
• A double-legged balance-optimization protocol may be an efficient method to determine a customized optimal stochastic resonance stimulation intensity that will transfer to improving single-legged balance for functional ankle instability.

Functional ankle instability (FAI) is a residual symptom of ankle sprains that often causes the sensation of “giving way” at the ankle and recurrent ankle sprains.¹ In addition, sensorimotor deficits associated with FAI are present as balance impairments.² Postural instabilities are important to identify because poor balance is a predisposing factor of ankle sprain injury.^3–5 Given that balance improvements associated with rehabilitation often take 6 weeks to occur,^6,7 a therapy, such as stochastic resonance stimulation (SRS), that facilitates balance improvements immediately⁸ or more quickly than rehabilitation alone^9,10 would be beneficial for individuals with FAI. Stochastic resonance stimulation is a therapy that introduces subsensory mechanical noise through the skin to enhance the ability of mechanoreceptors to detect and transmit weak signals related to balance.^11–13Natural noise created in the body can promote signal detection by amplifying weak sensory signals.^14,15 This natural noise occurs from external stimuli, physiologic processes, and biomechanics.^14,15 However, this internally generated noise may not be at a high enough level in some individuals to improve signal detection.^14,15 Healthy and injured individuals may benefit from SRS therapy when the level of naturally occurring noise is too low to facilitate signal detection.^14,15 Most evidence has indicated that individuals with and without sensorimotor impairments react similarly to SRS,^9,10,16–20 suggesting that the level of natural noise in the body is low enough for SRS to have positive treatment effects.Interestingly, however, Priplata et al¹⁸ reported that elderly participants had a better response to SRS than young healthy participants because the former used SRS to facilitate sensory signal detection to reduce sway. In addition, SRS improved balance in the elderly participants to within the normal range for young, healthy participants.¹⁸ Sensorimotor impairments are associated with age, and the naturally occurring noise in the elderly participants might not have contributed to signal detection.¹⁸ Thus, SRS corrected these sensorimotor deficits to facilitate balance improvements.¹⁸ Given the findings in the elderly participants,¹⁸ we postulate that the balance response to SRS might be better in individuals with FAI than in healthy individuals because FAI also is associated with sensorimotor deficits. Currently, no evidence exists to demonstrate that SRS produces better balance for FAI than stable ankles. Demonstrating that SRS improves balance more in FAI than stable ankles lends credence to the notion that this therapy enhances sensorimotor function.Recent evidence²¹ has indicated that the sensorimotor dysfunction with FAI may be due to reflex depressions, which can cause excessive sway with single-legged balance. These poor postural reflexes can result from an inability to integrate afferent input and efferent output.²² That is, diminished sensation from the foot and ankle may not detect signals related to postural control, leading to inappropriate muscle contractions that maintain stability. The inability to sense signals to generate adequate postural reflexes suggests that the naturally occurring internal noise is at a level too low to facilitate signal detection. To correct this sensorimotor impairment, SRS can serve as a pedestal to predispose mechanoreceptors to fire in the presence of real sensory signals, especially signals that otherwise would be undetectable.^11–13The traditional method for examining the effects of SRS on balance improvements is to apply the same subsensory intensity to all participants within a research study.^16–20 Subsensory intensities from 25% to 90% have enhanced balance in patients who are healthy, have diabetes, or have had a stroke.^16–20 Researchers¹⁷ also have presented preliminary data indicating that 75% of sensory threshold could be the optimal SRS intensity to affect the degree of balance improvements. This finding was confirmed in a second experiment¹⁷ when this specific SRS intensity was applied to all participants to optimize balance enhancements.Two research groups recently have proposed customizing the intensity of SRS applied to an individual to maximize treatment effects in lieu of applying the same intensity to all participants.^8,23 The rationale for this customized design was deduced from the early work of Collins et al,²⁴ who demonstrated that performance increased to a peak with increasing levels of SRS intensity and then decreased; however, the SRS intensity associated with this optimal intensity was slightly different for participants. In other words, the levels of SRS intensity for improving sensorimotor function must be fine tuned because subsensory intensities that are too low may not improve balance and those that are too high can diminish function.^{8,11,17,23,24} Furthermore, a customized SRS intensity is proposed for minimizing random error in datasets, potentially decreasing washout effects in a group analysis.⁸ Specifically related to FAI, researchers⁸ using 1 of 2 input SRS intensities have demonstrated that 92% of participants with FAI improved their single-legged balance with at least 1 input intensity, whereas 55% of them had impaired balance at the other input intensity. This finding suggests that using 1 intensity for all participants may have masked the treatment effects of SRS if the intensity that impaired balance was used for analysis.⁸ More recently, Mulavara et al²³ found that customizing the SRS intensity applied to an individual was crucial for maximizing balance improvements in healthy participants. These researchers defined an optimal intensity as the stimulus amplitude emitted from the SRS device that best improved balance over a control (no-SRS) condition.²³ By determining this customized optimal intensity for each individual, we speculate that treatment effects associated with SRS will increase compared with the same intensity for all participants.Double-legged balance tests are recommended for determining the treatment effects of SRS on stability.^16–20,23 These bipedal assessments allow individuals to maximize their stability with a wide base of support, providing a reliable means of determining the optimal SRS intensity. This recommended double-legged SRS protocol has not been tested in participants with FAI. Clinically, this protocol may be important to examine with FAI because balance can be assessed quickly when optimizing SRS intensity. Single-legged balance protocols may not be efficient for optimizing SRS intensity because of the number of unsuccessful trials associated with FAI. However, most researchers do not use single-legged balance as a criterion standard for assessing balance deficits associated with FAI² or quantifying treatment effects of SRS on FAI.^8–10 Therefore, for clinical applications, we propose using a double-legged balance protocol to quickly and efficiently optimize SRS intensity and then using this intensity to enhance single-legged balance. This optimization protocol may be more clinically relevant if the intensity for enhancing double-legged balance transfers to improving single-legged balance.Along these lines of clinical effectiveness, we believe that clinicians need to focus on 1 balance outcome measure when optimizing SRS intensity to improve stability. Common balance outcome measures that have improved with SRS over control conditions include sway velocity, excursion, and area.^16–20 Specifically related to FAI, resultant center-of-pressure velocity (COPV) has been used to assess the immediate effects of SRS on single-legged balance.⁸ Other balance measures also have been examined with SRS in participants with FAI, but all use center-of-pressure excursion (COPE) data points to compute the outcome measures (eg, COPV is computed by dividing excursion by time).^9,10 For clinical applicability, we have taken a minimalist approach in our study by selecting resultant COPV as our main outcome measure for the optimization protocol because it has detected balance improvements associated with SRS in participants with FAI.⁸Therefore, the initial purpose of our study was to determine if a customized optimal SRS intensity was better than a traditional SRS protocol (applying the same percentage sensory threshold intensity for all participants) for improving double- and single-legged balance in participants with and without FAI. Using a customized optimal SRS intensity, we wanted to determine (1) if individuals with FAI and individuals with stable ankles responded at different rates, (2) if double-legged balance (as measured by additional center-of-pressure measures) improved more with the optimal intensity than a control condition, and (3) if the optimal intensity for double-legged balance could transfer to improving single-legged balance over a control condition. Our hypotheses included the following: (1) The customized optimal SRS intensity protocol would improve double-legged balance better than the traditional protocol; (2) the treatment response to optimal SRS would be greater in individuals with FAI than in individuals with stable ankles; (3) the optimal intensity would improve double-legged balance more than a control condition; and (4) the optimal intensity would transfer to improving single-legged balance more than a control condition. The results of our study may be clinically relevant because a customized optimal SRS intensity level that maximally improves balance may enhance rehabilitation outcome measures and lead to greater ankle stability.     

Balance Training and Center-of-Pressure Location in Participants With Chronic Ankle Instability

Context:Chronic ankle instability (CAI) occurs in some people after a lateral ankle sprain and often results in residual feelings of instability and episodes of the ankle''s giving way. Compared with healthy people, patients with CAI demonstrated poor postural control and used a more anteriorly and laterally positioned center of pressure (COP) during a single-limb static-balance task on a force plate. Balance training is an effective means of altering traditional COP measures; however, whether the overall location of the COP distribution under the foot also changes is unknown.Objective:To determine if the spatial locations of COP data points in participants with CAI change after a 4-week balance-training program.Design:Randomized controlled trial.Setting:Laboratory.Intervention(s):Participants were randomly assigned to a 4-week balance-training program or no balance training.Results:Overall, COP position in the balance-training group shifted from being more anterior to less anterior in both eyes-open trials (before trial = 319.1 ± 165.4, after trial = 160.5 ± 149.5; P = .006) and eyes-closed trials (before trial = 387.9 ± 123.8, after trial = 189.4 ± 102.9; P < .001). The COP for the group that did not perform balance training remained the same in the eyes-open trials (before trial = 214.1 ± 193.3, after trial = 230.0 ± 176.3; P = .54) and eyes-closed trials (before trial = 326.9 ± 134.3, after trial = 338.2 ± 126.1; P = .69).Conclusions:In participants with CAI, the balance-training program shifted the COP location from anterolateral to posterolateral. The program may have repaired some of the damaged sensorimotor system pathways, resulting in a more optimally functioning and less constrained system.Key Words: sprains, rehabilitation, postural control

Key Points

• A 4-week progressive balance-training program effectively altered the spatial locations of center-of-pressure data points in participants with chronic ankle instability.
• The alteration in the spatial locations of center-of-pressure data points may indicate a more optimally functioning sensorimotor system.

Lateral ankle ligament injuries are among the most common injuries in the general population, active-duty military service members, and athletes.^1–4 Although the initial symptoms associated with lateral ankle sprains generally resolve in a short time, many patients continue to report residual problems, such as pain, instability, and feelings of the ankle''s giving way.⁵ These residual symptoms have been reported to last 6 to 18 months after initial injury and have been observed in 55% to 72% of patients.^6–8 Repeated incidences of lateral ankle instability, recurrent sprains with persistent symptoms, and diminished self-reported function have been termed chronic ankle instability (CAI).^9,10Postural control requires integration of visual, vestibular, and somatosensory input.¹¹ Somatosensory input combines contributions from cutaneous, articular, and musculotendinous receptors. Afferent information gathered from these 3 sources is processed within the central nervous system and used to control motor commands.¹² Deficient contributions from any of the afferent receptors can lead to diminished postural control.^12–15 Postural-control deficits have been found repeatedly in patients with CAI.^9,10,16–26 These deficits have been identified using a variety of outcome measures, including time to stabilization,^18,22 Star Excursion Balance Test (SEBT) reach distances,¹⁹ center-of-pressure (COP) excursion measures, and time-to-boundary (TTB) measures.^23,27The COP measures from force-plate data can be analyzed to determine the instantaneous point of application of ground reaction forces, and they are useful in evaluating the stability and function of the foot.²⁸ Recently, Pope et al²⁷ evaluated a novel measure, COP location, which involves examining the location of COP data points in relation to the plantar aspect of the foot. Identifying the COP location indicates where the forces are distributed on the foot and provides insight into the postural-control strategy being used. Traditional COP measures and TTB measures cannot elicit the mechanism a person is using to improve balance. The COP location provides information about the spatial distributions of force application under the foot. To determine the COP location, the foot was modeled into a rectangle and divided into 16 equal sections. While the participant performed a single-limb balance task on a force plate, the location of each COP data point was mapped into 1 of the 16 sections. Differences were found between uninjured participants and those with CAI.²⁷ Specifically, COP was more anteriorly and laterally positioned in participants with CAI compared with uninjured persons during eyes-open and eyes-closed single-legged standing.²⁷ The authors hypothesized that this spatial difference may represent a more constrained sensorimotor system and compensatory postural-control mechanisms in participants with CAI.²⁷ Having a more anterolateral COP is likely associated with the foot being more supinated, placing the ankle and subtalar joints in a closed-packed and more stable position that decreases feelings of instability in those with CAI.²⁷ However, this positioning moves the COP closer to the lateral border of support and consequently decreases the amount of time available for postural corrections in this direction.²⁷ Plantar-pressure studies have also demonstrated increased force and pressure concentration under the lateral midfoot and forefoot in participants with CAI during gait, which supports the notion of an anterior and lateral COP shift.^29–31Balance-training programs have been effective in improving postural control in participants with CAI.^28,32–37 McKeon et al²⁸ showed static and dynamic postural-control improvements in a sample of participants with CAI after 4 weeks of balance training that was intended to challenge their sensorimotor systems. Significant improvement occurred in self-reported function, magnitude and variability of TTB measures, and SEBT reach distances compared with pretest and control values.²⁸Although balance improvements have been found after rehabilitation in those with CAI, the neuromechanical mechanism driving these changes is unknown. Determining how the COP location in patients with CAI is affected by a balance-training program may be useful beyond simply evaluating traditional COP measures and also provide insight into how to restore normal function. Understanding how a balance-training rehabilitation program changes COP location offers information on the adaptation strategies participants with CAI use and may enable clinicians to more specifically target each person''s deficits. The purpose of our study, therefore, was to determine how balance training affected COP location. We hypothesized that COP location would be more posteriorly and medially positioned, similar to that of the uninjured participants, after balance training.     

Muscle-Activation Onset Times With Shoes and Foot Orthoses in Participants With Chronic Ankle Instability

Context

Participants with chronic ankle instability (CAI) use an altered neuromuscular strategy to shift weight from double-legged to single-legged stance. Shoes and foot orthoses may influence these muscle-activation patterns.

Objective

To evaluate the influence of shoes and foot orthoses on onset times of lower extremity muscle activity in participants with CAI during the transition from double-legged to single-legged stance.

Design

Cross-sectional study.

Setting

Musculoskeletal laboratory.

Patients or Other Participants

A total of 15 people (9 men, 6 women; age = 21.8 ± 3.0 years, height = 177.7 ± 9.6 cm, mass = 72.0 ± 14.6 kg) who had CAI and wore foot orthoses were recruited.

Intervention(s)

A transition task from double-legged to single-legged stance was performed with eyes open and with eyes closed. Both limbs were tested in 4 experimental conditions: (1) barefoot (BF), (2) shoes only, (3) shoes with standard foot orthoses, and (4) shoes with custom foot orthoses (SCFO).

Main Outcome Measure(s)

The onset of activity of 9 lower extremity muscles was recorded using surface electromyography and a single force plate.

Results

Based on a full-factorial (condition, region, limb, vision) linear model for repeated measures, we found a condition effect (F_3,91.8 = 9.39, P < .001). Differences among experimental conditions did not depend on limb or vision condition. Based on a 2-way (condition, muscle) linear model within each region (ankle, knee, hip), earlier muscle-activation onset times were observed in the SCFO than in the BF condition for the peroneus longus (P < .001), tibialis anterior (P = .003), vastus medialis obliquus (P = .04), and vastus lateralis (P = .005). Furthermore, the peroneus longus was activated earlier in the shoes-only (P = .02) and shoes-with-standard-foot-orthoses (P = .03) conditions than in the BF condition. No differences were observed for the hip muscles.

Conclusions

Earlier onset of muscle activity was most apparent in the SCFO condition for ankle and knee muscles but not for hip muscles during the transition from double-legged to single-legged stance. These findings might help clinicians understand how shoes and foot orthoses can influence neuromuscular control in participants with CAI.Key Words: footwear, insoles, ankle sprains, neuromuscular system, electromyography

Key Points

• Shoes and foot orthoses accelerated muscle-activation onset times of the ankle and knee but not the hip in participants with chronic ankle instability.
• Earlier muscle-activation onset times were most prominent in the shoes-with-custom-foot-orthoses condition.
• At the ankle, the muscle-activation onset time of the peroneus longus was earlier in the shoes-only, shoes-with-standard-foot-orthoses, and shoes-with-custom-foot-orthoses conditions than in the barefoot condition, and the muscle-activation onset time of the tibialis anterior was earlier in the shoes-with-custom-foot-orthoses condition than in the barefoot condition.
• At the knee, the muscle-activation onset times of the vastus medialis obliquus and vastus lateralis were earlier in the shoes-with-custom-foot-orthoses condition than in the barefoot condition.
• The results may help clinicians understand how shoes and foot orthoses can influence neuromuscular control of the lower extremity in participants with chronic ankle instability.

Lateral ankle sprains are estimated to account for approximately 15% of all sport injuries.¹ Even more concerning than the initial ankle sprain is the large proportion of patients with residual symptoms and recurrent ankle sprains for months to years after the initial injury.² The occurrence of repetitive ankle sprains and the feeling of the ankle “giving way” with slight or no perturbation has been defined as chronic ankle instability (CAI).³The transition task from double-legged to single-legged stance during barefoot (BF) conditions has been shown to discriminate between uninjured participants and participants with CAI. Researchers have reported that muscle-activation onset times typically were delayed^4,5 and postural stability was impaired⁶ in participants with CAI, indicating the use of another strategy to shift weight from double-legged to single-legged stance. However, it is unclear whether findings from BF tests represent typical daily situations when shoes, and for some persons foot orthoses, are often worn.The human foot is the first point of contact between the body and a supporting surface. The cutaneous mechanoreceptors on the planar surface of the foot are an important source of sensory information,⁷ which is considered essential for achieving and maintaining functional joint stability.⁸ Shoes and foot orthoses act as an interface between the body and a supporting surface and can influence the sensory feedback from these mechanoreceptors by increasing the contact area between the foot and the supporting surface.^7,9 Furthermore, the small kinematic alterations of the rear foot and tibia that have been described with the use of shoes and foot orthoses¹⁰ may put the ankle joint in a more neutral position, thereby improving the capacity of the ankle mechanoreceptors to provide more accurate proprioceptive input toward the central nervous system.¹¹ Changing the sensory input to these mechanisms consequently would change the motor output.⁷Evidence is increasing that shoes and foot orthoses can influence lower extremity muscle activation.^10,12–14 Dingenen et al¹⁴ were the first investigators to measure the influence of shoes and foot orthoses on muscle-activation onset times of the entire lower extremity in uninjured participants during the transition from double-legged to single-legged stance. Their results showed that shoes and foot orthoses can accelerate muscle-activation onset times of the peroneus longus. No differences were reported in more proximal muscles. Recently, researchers have suggested that future investigators should be focused on the influence of shoes and foot orthoses on neuromuscular control, especially in participants with injuries, such as CAI,^10,13,14 to increase our understanding of how positive clinical outcomes from the use of shoes and foot orthoses can be achieved.¹¹ Altering or improving proprioceptive information and muscle-activation patterns in participants with CAI would be clinically beneficial, given that their proprioceptive and neuromuscular deficits have been described.¹⁵To our knowledge, no investigators have focused on the influence of shoes and foot orthoses on muscle-activation onset times of the entire lower extremity in participants with CAI during the transition from double-legged to single-legged stance. Therefore, the purpose of our study was to evaluate the influence of shoes and foot orthoses on muscle-activation onset times during the transition from double-legged to single-legged stance in participants with CAI. Based on the proposed effects of shoes and foot orthoses on lower extremity neuromuscular control, we hypothesized that shoes and foot orthoses would accelerate muscle-activation onset times compared with a BF condition.     

Reliability and Sensitivity of the Foot and Ankle Disability Index in Subjects With Chronic Ankle Instability

Context: Despite the importance of patient's subjective reports of function, little research has addressed their use in the athletic population.Objective: To examine the following measurement properties of the Foot and Ankle Disability Index (FADI) and the FADI Sport: (1) intersession reliability during 1- and 6-week intervals, (2) sensitivity to differences between healthy subjects and subjects with chronic ankle instability (CAI), and (3) sensitivity to changes in function in those with CAI after rehabilitation.Design: Test-retest design.Setting: Laboratory setting.Patients or Other Participants: Fifty recreationally active subjects.Main Outcome Measure(s): FADI and FADI Sport.Results: Intraclass correlation coefficients (ICC 2,1) for the FADI and FADI Sport at 1 week were 0.89 and 0.84, respectively, for the involved limbs. Over 6 weeks, the ICC values for the involved limb of subjects who did not complete rehabilitation were 0.93 and 0.92, respectively. For both surveys, scores were significantly less for the involved limbs of subjects with CAI compared with their uninvolved limbs (P < .05). No significant side-to-side differences were noted among the healthy subjects. Scores on both surveys increased significantly after rehabilitation (FADI: P < .05, effect size = 0.52; FADI Sport: P < .05, effect size = 0.71).Conclusions: The FADI and FADI Sport appear to be (1) reliable in detecting functional limitations in subjects with CAI, (2) sensitive to differences between healthy subjects and subjects with CAI, and (3) responsive to improvements in function after rehabilitation in subjects with CAI.     

双膝骨关节炎对女性老年人踝关节策略动态平衡能力的影响

目的 探索双膝骨关节炎(knee osteoarthritis,KOA)对女性老年人踝关节策略动态平衡能力的影响.方法 采用动态平衡能力测试仪测试KOA患者(KOA组)和一般老年人(对照组)平衡得分、旋转速度、最大旋转速度、目标球在各区域的停留时间百分比等指标,并进行对比分析.结果 KOA组的平衡得分低于对照组;KOA...     

Weight-Bearing Dorsiflexion Range of Motion and Landing Biomechanics in Individuals With Chronic Ankle Instability

Context

People with chronic ankle instability (CAI) exhibit less weight-bearing dorsiflexion range of motion (ROM) and less knee flexion during landing than people with stable ankles. Examining the relationship between dorsiflexion ROM and landing biomechanics may identify a modifiable factor associated with altered kinematics and kinetics during landing tasks.

Objective

To examine the relationship between weight-bearing dorsiflexion ROM and single-legged landing biomechanics in persons with CAI.

Design

Cross-sectional study.

Setting

Laboratory.

Patients or Other Participants

Fifteen physically active persons with CAI (5 men, 10 women; age = 21.9 ± 2.1 years, height = 168.7 ± 9.0 cm, mass = 69.4 ± 13.3 kg) participated.

Intervention(s)

Participants performed dorsiflexion ROM and single-legged landings from a 40-cm height. Sagittal-plane kinematics of the lower extremity and ground reaction forces (GRFs) were captured during landing.

Main Outcome Measure(s)

Static dorsiflexion was measured using the weight-bearing–lunge test. Kinematics of the ankle, knee, and hip were observed at initial contact, maximum angle, and sagittal displacement. Sagittal displacements of the ankle, knee, and hip were summed to examine overall sagittal displacement. Kinetic variables were maximum posterior and vertical GRFs normalized to body weight. We used Pearson product moment correlations to evaluate the relationships between dorsiflexion ROM and landing biomechanics. Correlations (r) were interpreted as weak (0.00–0.40), moderate (0.41–0.69), or strong (0.70–1.00). The coefficient of determination (r²) was used to determine the amount of explained variance among variables.

Results

Static dorsiflexion ROM was moderately correlated with maximum dorsiflexion (r = 0.49, r² = 0.24), ankle displacement (r = 0.47, r² = 0.22), and total displacement (r = 0.67, r² = 0.45) during landing. Dorsiflexion ROM measured statically and during landing demonstrated moderate to strong correlations with maximum knee (r = 0.69–0.74, r² = 0.47–0.55) and hip (r = 0.50–0.64, r² = 0.25–0.40) flexion, hip (r = 0.53–0.55, r² = 0.28–0.30) and knee (r = 0.53–0.70, r² = 0.28–0.49) displacement, and vertical GRF (−0.47– −0.50, r² = 0.22–0.25).

Conclusions

Dorsiflexion ROM was moderately to strongly related to sagittal-plane kinematics and maximum vertical GRF during single-legged landing in persons with CAI. Persons with less dorsiflexion ROM demonstrated a more erect landing posture and greater GRF.Key Words: ankle sprain, drop landing, neuromuscular control, kinematics, kinetics

Key Points

• During a single-legged landing, persons with chronic ankle instability demonstrated moderate to strong relationships between dorsiflexion range of motion (ROM) and sagittal-plane kinematics at the knee and hip and vertical ground reaction forces.
• Persons with less dorsiflexion ROM exhibited a less flexed landing strategy that attenuated ground reaction forces less efficiently.
• Identifying dorsiflexion deficits may enable clinicians to implement interventions to increase ROM and potentially modify the landing biomechanics that persons with chronic ankle instability exhibit.

Ankle sprains are one of the most common injuries associated with athletics.¹ In addition, up to 73% of athletes who sustain ankle sprains experience recurrent ankle sprains, and 59% report functional loss and residual symptoms that have affected athletic performance.² Residual symptoms resulting from ankle sprains are often associated with a condition known as chronic ankle instability (CAI). This condition is characterized by repetitive ankle-sprain injuries, frequent episodes of the ankle “giving way,” and decreased self-reported function stemming from an acute ankle sprain.³ Persons with CAI have reported diminished health-related quality of life and are at greater risk for developing posttraumatic ankle osteoarthritis.^4,5 Based on the number of persons who develop CAI and the long-term consequences of the condition, a better understanding of the contributing factors is warranted to improve clinical intervention strategies.Chronic ankle instability may be associated with several mechanical impairments in ankle function,³ including a deficit in ankle-joint dorsiflexion range of motion (ROM).^3,6 Whereas the exact prevalence of dorsiflexion ROM deficits has not been determined, 30% to 74% of persons with CAI have at least a 5° deficit in weight-bearing dorsiflexion ROM compared with the contralateral limb.^7,8 The exact origin of dorsiflexion ROM deficits is unclear, but it likely results from arthrokinematic alterations and adaptive shortening of the triceps surae muscle group.^9,10 More importantly, dorsiflexion deficits may limit the ability to fully achieve a closed-packed, stable position of the ankle during dynamic activities, such as gait and landing, which may promote the pathomechanics associated with ankle-sprain mechanisms.^9,11,12 Therefore, a cascade of structural impairments leading to decreased dorsiflexion ROM may affect the ability to execute functional activities and ultimately contribute to the repeated ankle sprains and episodes of giving way related to CAI.Dorsiflexion ROM plays a prominent role in the biomechanics of tasks that require landing.¹³ Greater passive open chain dorsiflexion ROM has been associated with greater hip and knee flexion and lower ground reaction forces (GRFs) during a jump-landing task in healthy persons.¹³ Those with greater dorsiflexion ROM land with a less erect posture by using greater sagittal-plane displacement, which allows the body to attenuate forces more efficiently.¹³ Therefore, the available amount of dorsiflexion ROM may influence function not only at the ankle but also at more proximal structures in the lower extremity. Persons with CAI have demonstrated less dorsiflexion ROM during gait^11,14 and less knee flexion during landing than persons without CAI, but these findings have not been consistent in the literature.^15,16 Furthermore, persons with CAI have shown greater energy dissipation at the ankle and less energy dissipation at the knee.¹⁷ Cumulatively, these observations suggest that alterations exist in the distal to proximal linkage of the kinetic chain of the lower extremity in persons with CAI.¹⁷ Further examining a potential connection between dorsiflexion ROM and landing biomechanics may provide additional insight into these findings.Persons who have CAI and less dorsiflexion ROM may also exhibit more erect landing postures and greater GRF, which may have implications for sustaining future lower extremity injuries or episodes of giving way.^18,19 Examining this relationship may further support integrating clinical intervention strategies that target dorsiflexion ROM into the rehabilitation of persons with CAI.⁹ Therefore, the purpose of our study was to examine the relationship between dorsiflexion ROM and single-legged landing biomechanics in persons with CAI. We examined dorsiflexion ROM statically, using the weight-bearing–lunge test, and dynamically, using motion capture, to determine its relationship to landing biomechanics. In addition, we focused on the sagittal-plane kinematics of the lower extremity and GRFs to explore how dorsiflexion ROM may influence force attenuation in persons with CAI. Kinematics were examined in the sagittal plane because it is primarily responsible for force attenuation during landing tasks.²⁰ We hypothesized that persons with less dorsiflexion ROM would exhibit less sagittal-plane motion throughout the lower extremity and greater GRF during a single-legged drop-landing task.     

Proprioception and Muscle Strength in Subjects With a History of Ankle Sprains and Chronic Instability

OBJECTIVE: To examine if patients with chronic ankle instability or a history of ankle sprains without chronic instability have worse proprioception or less invertor and evertor muscle strength. DESIGN AND SETTING: We assessed proprioception and muscle strength on the Biodex isokinetic dynamometer in the laboratory of the Department of Sports Medicine, University Hospital Ghent. SUBJECTS: Subjects included 87 physical education students (44 men, 43 women, age = 18.33 +/- 1.25 years, mass = 66.09 +/- 8.11 kg, height = 174.11 +/- 8.57 cm) at the University of Ghent in Belgium. Their ankles were divided into 4 groups: a symptom-free control group, subjects with chronic ankle instability, subjects who had sustained an ankle sprain in the last 2 years without instability, and subjects who sustained an ankle sprain 3 to 5 years earlier without instability. MEASUREMENTS: Active and passive joint-position sense was assessed at the ankle, and isokinetic peak torque was determined for concentric and eccentric eversion and inversion movements at the ankle. RESULTS: Statistical analysis indicated significantly less accurate active position sense for the instability group compared with the control group at a position close to maximal inversion. The instability group also showed a significantly lower relative eversion muscle strength (% body weight). No significant differences were observed between the control group and the groups with past sprains without instability. CONCLUSIONS: We suggest that the possible cause of chronic ankle instability is a combination of diminished proprioception and evertor muscle weakness. Therefore, we emphasize proprioception and strength training in the rehabilitation program for ankle instability.     

Biomechanical Response to External Biofeedback During Functional Tasks in Individuals With Chronic Ankle Instability

ContextAltered biomechanics displayed by individuals with chronic ankle instability (CAI) is a possible cause of recurring injuries and posttraumatic osteoarthritis. Current interventions are unable to modify aberrant biomechanics, leading to research efforts to determine if real-time external biofeedback can result in changes.ObjectiveTo determine the real-time effects of visual and auditory biofeedback on functional-task biomechanics in individuals with CAI.DesignCrossover study.SettingLaboratory.Patients or Other ParticipantsNineteen physically active adults with CAI (7 men, 12 women; age = 23.95 ± 5.52 years, height = 168.87 ± 6.94 cm, mass = 74.74 ± 15.41 kg).Intervention(s)Participants randomly performed single-limb static balance, step downs, lateral hops, and forward lunges during a baseline and 2 biofeedback conditions. Visual biofeedback was given through a crossline laser secured to the dorsum of the foot. Auditory biofeedback was given through a pressure sensor placed under the lateral foot and connected to a buzzer that elicited a noise when pressure exceeded the set threshold. Cues provided during the biofeedback conditions were used to promote proper biomechanics during each task.Main Outcome Measure(s)We measured the location of center-of-pressure (COP) data points during balance with eyes open and eyes closed for each condition. Plantar pressure in the lateral column of the foot during functional tasks was extracted. Secondary outcomes of interest were COP area and velocity, time to boundary during static balance, and additional plantar-pressure measures.ResultsBoth biofeedback conditions reduced COP in the anterolateral quadrant while increasing COP in the posteromedial quadrant of the foot during eyes-open balance. Visual biofeedback increased lateral heel pressure and the lateral heel and midfoot pressure-time integral during hops. The auditory condition produced similar changes during the eyes-closed trials. Auditory biofeedback increased heel pressure during step downs and decreased the lateral forefoot pressure-time integral during lunges.ConclusionsReal-time improvements in balance strategies were observed during both external biofeedback conditions. Visual and auditory biofeedback appeared to effectively moderate different functional-task biomechanics.     

Fatigue-Induced Alterations of Static and Dynamic Postural Control in Athletes With a History of Ankle Sprain

Context:

Sensorimotor control is impaired after ankle injury and in fatigued conditions. However, little is known about fatigue-induced alterations of postural control in athletes who have experienced an ankle sprain in the past.

Objective:

To investigate the effect of fatiguing exercise on static and dynamic balance abilities in athletes who have successfully returned to preinjury levels of sport activity after an ankle sprain.

Design:

Cohort study.

Setting:

University sport science research laboratory.

Patients or Other Participants:

30 active athletes, 14 with a previous severe ankle sprain (return to sport activity 6–36 months before study entry; no residual symptoms or subjective instability) and 16 uninjured controls.

Intervention(s):

Fatiguing treadmill running in 2 experimental sessions to assess dependent measures.

Main Outcome Measure(s):

Center-of-pressure sway velocity in single-legged stance and time to stabilization (TTS) after a unilateral jump-landing task (session 1) and maximum reach distance in the Star Excursion Balance Test (SEBT) (session 2) were assessed before and immediately after a fatiguing treadmill exercise. A 2-factorial linear mixed model was specified for each of the main outcomes, and effect sizes (ESs) were calculated as Cohen d.

Results:

In the unfatigued condition, between-groups differences existed only for the anterior-posterior TTS (P = .05, ES = 0.39). Group-by-fatigue interactions were found for mean SEBT (P = .03, ES = 0.43) and anterior-posterior TTS (P = .02, ES = 0.48). Prefatigue versus postfatigue SEBT and TTS differences were greater in previously injured athletes, whereas static sway velocity increased similarly in both groups.

Conclusions:

Fatiguing running significantly affected static and dynamic postural control in participants with a history of ankle sprain. Fatigue-induced alterations of dynamic postural control were greater in athletes with a previous ankle sprain. Thus, even after successful return to competition, ongoing deficits in sensorimotor control may contribute to the enhanced ankle reinjury risk.Key Words: sensorimotor control, neuromuscular activity, copers, balance, time to stabilization, Star Excursion Balance Test

Key Points

• When athletes were tested in the unfatigued state, only minimal differences in postural control were detected between athletes who had fully recovered from an ankle sprain and uninjured controls.
• Injured participants experienced larger fatigue-induced alterations of dynamic postural control than healthy controls.
• Persistent sensorimotor control deficits in recovered athletes might remain undetected in the unfatigued state.

Ankle sprains are the most common game-related injuries in team ball-sport athletes,¹ and are often associated with decreases in sensorimotor control, including proprioception (reduced joint position sense and kinesthesia), muscular strength, and balance performance (static and dynamic postural control). These alterations have been reported in individuals after acute ankle sprain^2,3 and in those with chronic ankle instability (CAI).^2,3 Along with additional complaints, such as swelling, pain, or episodes of “giving way,” sensorimotor deficits persist even years after injury.^4,5 Consequently, sensorimotor impairments associated with lower extremity injuries may contribute to performance impairments⁶ and increase the reinjury risk.⁷ Athletes who successfully return to high-level sports activities and report normal function without persistent complaints have previously been defined as copers.⁸ However, recent studies suggest that even though functional performance and self-reported disability in ankle-sprain copers are similar to those in individuals who have never sustained an ankle sprain,⁸ sensorimotor control might still be affected.^9,10The incidence of match injuries in soccer players increases toward the end of both halves,¹¹ suggesting that physical fatigue might play an important role in injury-related sensorimotor control changes. This concept is supported by a number of studies examining sensorimotor alterations after fatiguing exercise in healthy, uninjured participants; among the observed changes were reduced muscle strength and activity,¹² and altered proprioception¹³ and kinematics.¹⁴ Additionally, static postural control was assessed in most of these studies, showing an increase in postural sway due to localized fatigue of the ankle,¹⁵ knee, and hip¹⁶ muscles that can persist up to 10 minutes after exercise ends.¹⁷ Comparable results have been shown for fatiguing multijoint exercises¹⁷ and whole-body fatigue.¹⁸ Authors of only 2 studies have investigated the effects of fatiguing exercises on dynamic measures of postural control in healthy individuals¹⁹ and participants with CAI²⁰; however, because of different study populations and testing modalities, the effects remain uncertain.The findings described above suggest that long-term impairment of sensorimotor control exists after an ankle sprain and may even be present in those who do not develop persistent functional impairments and successfully return to preinjury levels of sport activity. To our knowledge, only 1 study²⁰ specifically investigated the effect of exercise-induced fatigue on participants with a previous ankle injury. Based on the findings of Gribble et al,²⁰ we hypothesize that these impairments are small under regular conditions but could expose athletes to an increased injury risk when they physically fatigue during intensive exercise.Therefore, the aim of our study was to investigate fatigue-induced alterations of static and dynamic postural control in a sample of ankle sprain copers and to compare the effects with those of uninjured controls. We proposed that changes in postural control due to fatigue would be more substantial in previously injured participants than in controls.     

长期太极拳和慢跑锻炼对侧向突发干扰下老年男性神经肌肉反应时和肌电达峰值时间影响

目的比较长期太极拳和慢跑锻炼对老年男性突发侧向姿势干扰下神经肌肉反应时和肌电达峰值时间的差异,探索提高老年男性侧向姿势挑战下神经肌肉反应和肌肉收缩效率的有效锻炼方式。方法利用足底水平干扰触发平台对年轻男性、无规律锻炼的老年男性、长期慢跑锻炼的老年男性、长期太极拳锻炼的老年男性进行突发侧向姿势干扰。表面肌电测试和分析系统用于收集腓骨长肌、胫骨前肌、臀中肌和竖脊肌的肌电信号。结果突发侧向干扰下,无规律锻炼老年男性腓骨长肌、胫骨前肌和臀中肌的神经肌肉反应时明显地慢于年轻男性,长期太极拳锻炼老年男性胫骨前肌和竖脊肌的神经肌肉反应明显地快于老年对照组;年轻男性腓骨长肌、胫骨前肌和臀中肌的收缩速度明显地快于3组老年人。结论长期太极拳锻炼可以使老年男性踝关节和躯干肌的神经肌肉反应更加迅速以应对侧向的姿势挑战,而对于提高老年男性肌肉收缩效率的效果不明显。     

Dynamic posturography in Parkinson's disease: diagnostic utility of the “first trial effect”

Previous dynamic posturography studies demonstrated clear abnormalities in balance responses in Parkinson's disease (PD) patients compared to controls at the group level, but its clinical value in the diagnostic process and fall risk estimation in individual patients leaves for improvement. Therefore, we investigated whether a new approach, focusing on the balance responses to the very first and fully unpractised trial rather than a pooled mean response to a series of balance perturbations, could further improve the diagnostic utility of dynamic posturography. Following the first trial, subjects were exposed to repeated balance perturbations, which also permitted us to investigate the training responses. Fourteen patients with PD and 18 age-matched controls were enrolled, who received a series of multidirectional postural perturbations, induced by support surface rotations. We measured trunk and upper arm kinematics and electromyographic responses, and evaluated group differences at three levels: the postural response to the very first backward perturbation; pooled first and habituated postural responses; and habituation rates. Analysis of the first trial responses yielded similar results as evaluation of the mean response over trials: forward flexion of the trunk induced by backward perturbations was decreased in patients, accompanied by increased muscle responses present. Moreover, trunk movement and muscle activity were equally present in both groups—suggesting a preserved training response in PD patients. Early masseter activity in both groups might be indicative of a startle-like component to the balance response. In terms of diagnostic utility, focusing on the first trial response or habituation rate is no better than analysis of pooled responses to a series of perturbations. The apparently preserved training response in PD patients suggests that balance reactions in PD can be improved by repeated exposure, and this may have implications for future exercise studies. Early masseter activity warrants further studies to evaluate a potential startle component in the pathophysiology of balance disorders.     

Predisposing Factors Associated With Chronic and Recurrent Rhinosinusitis in Childhood

Purpose

There is currently no information regarding predisposing factors for chronic and recurrent rhinosinusitis (RS), although these are considered to be multifactorial in origin, and allergic diseases contribute to their pathogenesis. We evaluated the predisposing factors that may be associated with chronic and recurrent RS.

Methods

In this prospective study, we examined patients with RS younger than 13 years of age, diagnosed with RS at six tertiary referral hospitals in Korea between October and December, 2006. Demographic and clinical data related to RS were recorded and analyzed.

Results

In total, 296 patients were recruited. Acute RS was the most frequent type: 56.4% of the patients had acute RS. The prevalences of other types of RS, in descending order, were chronic RS (18.9%), subacute RS (13.2%), and recurrent RS (11.5%). Factors associated with recurrent RS were similar to those of chronic RS. Patients with chronic and recurrent RS were significantly older than those with acute and subacute RS. The prevalences of allergic rhinitis, atopy, and asthma were significantly higher in patients with chronic and recurrent RS than those with acute and subacute RS.

Conclusions

An association between atopy and chronic/recurrent RS, compared to acute and subacute RS, suggests a possible causal link.