Alan R. Needle

Muscle Spindle Traffic in Functionally Unstable Ankles During Ligamentous Stress

CONTEXT Ankle sprains are common in athletes, with functional ankle instability (FAI) developing in approximately half of cases. The relationship between laxity and FAI has been inconclusive, suggesting that instability may be caused by insufficient sensorimotor function and dynamic restraint. Research has suggested that deafferentation of peripheral mechanoreceptors potentially causes FAI; however, direct evidence confirming peripheral sensory deficits has been elusive because previous investigators relied upon subjective proprioceptive tests. OBJECTIVE To develop a method for simultaneously recording peripheral sensory traffic, joint forces, and laxity and to quantify differences between healthy ankles and those with reported instability. DESIGN Case-control study. SETTING University laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 29 participants (age = 20.9 ± 2.2 years, height = 173.1 ± 8.9 cm, mass = 74.5 ± 12.7 kg) stratified as having healthy (HA, n = 19) or unstable ankles (UA, n = 10). INTERVENTION(S) Sensory traffic from muscle spindle afferents in the peroneal nerve was recorded with microneurography while anterior (AP) and inversion (IE) stress was applied to ligamentous structures using an ankle arthrometer under test and sham conditions. MAIN OUTCOME MEASURE(S) Laxity (millimeters or degrees) and amplitude of sensory traffic (percentage) were determined at 0, 30, 60, 90, and 125 N of AP force and at 0, 1, 2, 3, and 4 Nm of IE torque. Two-factor repeated-measures analyses of variance were used to determine differences between groups and conditions. RESULTS No differences in laxity were observed between groups (P > .05). Afferent traffic increased with increased force and torque in test trials (P < .001). The UA group displayed decreased afferent activity at 30 N of AP force compared with the HA group (HA: 30.2% ± 9.9%, UA: 17.1% ± 16.1%, P < .05). CONCLUSIONS The amplitude of sensory traffic increased simultaneously with greater ankle motion and loading, providing evidence of the integrated role of capsuloligamentous and musculotendinous mechanoreceptors in maintaining joint sensation. Unstable ankles demonstrated diminished afferent traffic at low levels of force, suggesting the early detection of joint loading may be compromised.

Effect of elastic taping on postural control deficits in subjects with healthy ankles, copers, and individuals with functional ankle instability.

Background: Ankle sprains are the most common injury among physically active people, with common sequelae including repeated episodes of giving way, termed functional ankle instability. Copers are a cohort in ankle research comprised of those who have sprained their ankle but have not suffered any further dysfunction. The use of an elastic tape, Kinesio Tape, in sports medicine practice has recently gained popularity and may help improve postural control deficits related to functional ankle instability. The purpose of this study was to examine the immediate and prolonged effects of Kinesio Taping on postural control in healthy, coper, and unstable ankles as measured through single-limb balance on a force plate. Methods: Sixty physically active, college-aged participants (72.5 ± 9.7 cm, 74.2 ± 16.2 kg, 21.5 ± 2.6 years) were stratified into healthy, coper, or unstable groups using the Cumberland Ankle Instability Tool (CAIT) combined with their history of ankle injury. Dependent variables included time-to-boundary (TTB) measures and traditional center of pressure (COP) measures in both the mediolateral (frontal) and anteroposterior (sagittal) planes. Testing was performed prior to tape application, immediately after application of the tape, 24 hours following tape application, and immediately after tape removal. Results: Significant differences between groups were observed for COP standard deviation and range in the sagittal plane. Significant differences between tape conditions for TTB absolute minima and standard deviation were also noted. Post hoc testing revealed large to medium effect sizes for the group differences and very small effect sizes for the differences between conditions. Conclusions: Our study did not reveal decisively relevant changes following application of Kinesio Tape to the ankle. However, we did observe sagittal plane postural control deficits in subjects with ankle instability measured through summary COP variables over 20-second trials. Clinical Relevance: Ankle instability is a concern for many clinicians. Kinesio Taping, although a popular form of clinical intervention, remains understudied. Evidence from this study does not support the use of Kinesio Taping for improving postural control deficits in those with ankle instability.

Neuromechanical coupling in the regulation of muscle tone and joint stiffness

The ability of the nervous system to accommodate changes to joint mechanics is crucial in the maintenance of joint stability and the prevention of injury. This neuromechanical coupling is achieved through several mechanisms such as the central and peripheral regulation of muscle tone and subsequent alterations to joint stiffness. Following joint injury, such as a ligamentous sprains, some patients develop functional instability or require surgery to stabilize the joint, while others are able to cope and display limited impairments. Several researchers have attempted to explain these divergent outcomes, although research using proprioceptive tasks and quantifying reaction times has led to equivocal results. Recent innovations have allowed for the simultaneous measurement of mechanical and nervous system function among these subsets. The intent of this review was to explore the relationships between joint stiffness and nervous system function, and how it changes following injury. By better understanding these mechanisms, researchers and clinicians may better develop and implement rehabilitation protocols to target individual deficits among injured populations.

The effects of ankle Kinesio taping on ankle stiffness and dynamic balance.

The purpose of this study was to determine the effects of Kinesio® taping on static restraint and dynamic postural control of the ankle joint. Thirty female subjects with no history of ankle injury participated in this study. Subjects were tested for passive ankle laxity and stiffness, and time to stabilization following forward, backward, medial, and lateral hops. Subjects were tested prior to tape application, immediately following application, and following 24 hours of use. Differences between taping conditions were investigated using analyses of variance and pairwise comparisons. Stiffness increased following initial application and 24 hours of Kinesio® tape use (F = 6.99, p = .003), despite no observed changes in ankle laxity (F = 0.77, p = .49); however, no changes were observed in time-to-stabilization (F = 0.03, p = .97). Our results suggest that Kinesio® tape may improve static restraint in the ankle joint without altering peak motion or dynamic postural control. A future investigation into Kinesio® tape efficacy in injury prevention or rehabilitation is warranted.

Role of external prophylactic support in restricting accessory ankle motion after exercise.

Background: To both prevent and accelerate recovery and return-to-play from ankle sprains, clinicians frequently employ the use of external prophylactic support (EPS), such as taping and bracing, to provide mechanical support to the ankle joint. While common practice clinically, research has been inconclusive in demonstrating the effectiveness of EPS in restricting accessory motion (laxity) throughout activity, as well as its efficacy in restricting laxity in patients with complaints of ankle instability, and patients with a history of ankle sprain. The purpose of this study was to investigate the effectiveness of EPS type (None, Tape, Brace) on ankle laxity before and after exercise in subjects with varying degrees of previous ankle injury. Methods: Ankles from 24 participants (age, 20.6 ± 1.6 years; height, 173.6 ± 8.3 cm; mass, 72.8 ± 12.2 kg) were placed into one of three groups: healthy control (CON), potential coper (COP), and functionally unstable (UNS). Ankle laxity was assessed using an ankle arthrometer at 4 points in time; prior to EPS application, immediately following EPS application, following a 20-minute functional exercise protocol with EPS, and following removal of EPS. Peak ankle anterior displacement (ANT), inversion rotation (INV), and eversion rotation (EVR) were compared between groups and across conditions using a three-way ANOVA. Results: Taping and bracing each decreased laxity from pre-application to pre-exercise and post-exercise. Tape provided greater restriction post-exercise in inversion and eversion rotation. Additionally, the UNS group demonstrated significantly greater anterior displacement post-exercise following removal of the brace compared to other groups. Conclusion: Compared to pre-application and post-removal, EPS significantly decreased ankle laxity before and after physical activity, with taping providing better restriction in inversion and eversion rotation throughout exercise. Clinical Relevance: Following EPS removal, bracing revealed a greater increase in post-exercise laxity in subjects with ankle instability, suggesting tape may be more beneficial for controlling laxity in these patients.

Lower-leg Kinesio tape reduces rate of loading in participants with medial tibial stress syndrome

CONTEXT Medial tibial stress syndrome (MTSS) is an overuse injury occurring among the physically active. Linked to increased strain on the medial tendons of the ankle, studies emphasize controlling medial foot loading in the management of this condition. Kinesio taping (KT) has gained popularity for treating musculoskeletal pathologies; however, its effect on MTSS remains uninvestigated. This study aimed to determine if healthy participants and patients with current or previous history of MTSS differ in the rate of loading, and if KT affects plantar pressures in these participants. METHODS Twenty healthy participants and 20 participants with current or previous history of MTSS were recruited and walked across a plantar pressure mat prior to KT application, immediately after application, and after 24-h of continued use. Time-to-peak force was measured in 6 foot areas and compared across groups and conditions. RESULTS ANOVA revealed a significant interaction between group, condition, and foot area (F = 1.990, p = 0.033). MTSS participants presented with lower medial midfoot time-to-peak force before tape application (95%CI: 0.014-0.160%, p = 0.021) that significantly increased following tape application (p < 0.05). CONCLUSIONS These results suggest that KT decreases the rate of medial loading in MTSS patients. Future research might assess mechanisms by which this effect is achieved.

Central Nervous System Adaptation After Ligamentous Injury: a Summary of Theories, Evidence, and Clinical Interpretation

The array of dysfunction occurring after ligamentous injury is tied to long-term clinical impairments in functional performance, joint stability, and health-related quality of life. To appropriately treat individuals, and in an attempt to avoid sequelae such as post-traumatic osteoarthritis, investigators have sought to better establish the etiology of the persistent dysfunction present in patients who have sustained joint ligament injuries to the lower extremities. Recent evidence has suggested that changes within the brain and central nervous system may underlie these functional deficits, with support arising from direct neurophysiologic measures of somatosensory dysfunction, motor system excitability, and plasticity of neural networks. As research begins to utilize these findings to develop targeted interventions to enhance patient outcomes, it is crucial for sports medicine professionals to understand the current body of evidence related to neuroplasticity after ligamentous injury. Therefore, this review provides (1) a comprehensive and succinct overview of the neurophysiologic techniques utilized in assessing central nervous system function after ligamentous injury, (2) a summary of the findings of previous investigations utilizing these techniques, and (3) direction for further application of these techniques in the prevention and rehabilitation of joint injury.

Atypical cortical drive during activation of the paretic and nonparetic tibialis anterior is related to gait deficits in chronic stroke.

OBJECTIVE The role of cortical drive in stroke recovery for the lower extremity remains ambiguous. The purpose of this study was to investigate the relationship between cortical drive and gait speed in a group of stroke survivors. METHODS Eighteen individuals with stroke were dichotomized into fast or slow walking groups. Transcranial magnetic stimulation (TMS) was used to collect motor evoked potentials (MEPs) from the tibialis anterior of each lower extremity during rest, paretic muscle contractions, and nonparetic muscle contractions. An asymmetry-index (AI) was calculated using motor thresholds and compared between groups. The average MEP of the paretic leg during TMS at maximal intensity (MEP100) for each condition was compared within and between groups. RESULTS A significant positive correlation was found between AI and walking speed. Slow-walkers had greater MEP100s during the nonparetic contraction than during the paretic contraction or rest conditions. In contrast, fast-walkers had greatest MEP100s during the paretic contraction. CONCLUSIONS Alterations in the balance of corticomotor excitability occur in the lower extremity of individuals with poor motor recovery post-stroke. This atypical cortical drive is dependent on activation of the unaffected hemisphere and contraction of the nonparetic leg. SIGNIFICANCE Understanding mechanisms underlying motor function can help to identify specific patient deficits that impair function.

The use of a single inertial sensor to estimate 3-dimensional ground reaction force during accelerative running tasks

The purpose of this investigation was to determine the feasibility of using a single inertial measurement unit (IMU) placed on the sacrum to estimate 3-dimensional ground reaction force (F) during linear acceleration and change of direction tasks. Force plate measurements of F and estimates from the proposed IMU method were collected while subjects (n=15) performed a standing sprint start (SS) and a 45° change of direction task (COD). Error in the IMU estimate of step-averaged component and resultant F was quantified by comparison to estimates from the force plate using Bland-Altman 95% limits of agreement (LOA), root mean square error (RMSE), Pearsons product-moment correlation coefficient (r), and the effect size (ES) of the differences between the two systems. RMSE of the IMU estimate of step-average F ranged from 37.70 N to 77.05 N with ES between 0.04 and 0.47 for SS while for COD, RMSE was between 54.19 N to 182.92 N with ES between 0.08 and 1.69. Correlation coefficients between the IMU and force plate measurements were significant (p≤0.05) for all values (r=0.53 to 0.95) except the medio-lateral component of step-average F. The average angular error in the IMU estimate of the orientation of step-average F was ≤10° for all tasks. The results of this study suggest the proposed IMU method may be used to estimate sagittal plane components and magnitude of step-average F during a linear standing sprint start as well as the vertical component and magnitude of step-average F during a 45° change of direction task.

A sex comparison of reactive knee stiffness regulation strategies under cognitive loads.

BACKGROUND Sex differences may exist in cognitive faculties and neuromuscular strategies for maintaining joint stability. The purpose of this study was to assess whether preparatory and reactive knee stiffening strategies are affected differently in males and females exposed to sex-biased cognitive loads. METHODS 20 male and 20 female volunteers were tested for knee joint stiffness and quadriceps and hamstring muscle activation patterns throughout a rapid eccentric knee extension perturbation. Participants were tested under 3 cognitive loads (Bentons Judgment of Line Orientation; Symbol Digit modalities Test; and Serial 7s) and a control condition. Apparent knee joint stiffness and muscle activation amplitude and timing were quantified throughout the perturbation across the 4 conditions. FINDINGS Reactive knee stiffness values were significantly less during the cognitive tasks compared to the control condition (Judgment of Line Orientation=0.034Nm/deg/kg, Symbol Digit Modalities Test=0.037Nm/deg/kg, Serial 7s=0.037Nm/deg/kg, control=0.048Nm/deg/kg). Females had greater normalized total apparent stiffness than males. The quadriceps muscles had faster and greater activation than the hamstring muscles; however, no group differences were observed. No overall differences in muscle activation (magnitude and timing) were found between the cognitive loading tasks. INTERPRETATION Cognitive loading may decrease the ability of healthy individuals to reactively stiffen their knee joint and appears to interfere with the normal stiffness regulation strategies. This may elucidate an extrinsic risk factor for non-contact knee ligament injury.