Mary Beth Badke

Effect of knee joint laxity on long-loop postural reflexes: evidence for a human capsular-hamstring reflex

SummaryThe onset latency and discharge amplitude of preprogrammed postural responses were evaluated in order to determine if the structure of synergistic activation could be altered by ligamentous laxity at the knee joint. Twelve subjects with unilateral and one subject with bilateral anterior cruciate ligament (ACL) insufficiency were tested while standing on a moveable platform. External balance perturbations (6 cm anterior or posterior horizontal displacements of the platform) were presented at velocities ranging from 15 to 35 cm/s. Perturbations were presented under the following experimental conditions: unilateral and bilateral stance, knees fully straight or flexed, and with ankle motion restricted or free. These stance, knee position, and ankle motion conditions were introduced to alter the stress transmitted to the knee joint during movement of the support surface. The automatic postural response was recorded from the tibialis anterior (T), quadriceps (Q), and medial hamstrings muscles (H) bilaterally. The normal response to an externally induced backward sway involved the automatic activation of T and Q at latencies of 80 ms and 90 ms respectively. Activation of the hamstrings in the non-injured extremity was not coupled with the postural response. Hamstrings are not typically involved in the correction posterior sway because H activation would tend to pull the center of mass further backwards. However, when the response in the ACL-deficient extremity was compared to the non-injured limb: (1) the automatic postural response in the ACL-deficient extremity was restructured to include hamstrings activation (100 ms latency), (2) H activation time was faster and less variable in the ACL-deficient limb, and (3) the ratio of H/Q discharge amplitude integrated over 100 ms and 200 ms from the onset of EMG activation showed a dominance of hamstring activity during unilateral stance on the lax limb. In addition, H/Q ratios integrated over 200 ms showed dominant hamstring activity in the ACL-deficient limb during bilateral stance. (4) Crosslimb comparisons showed greater normalized IEMG amplitudes for T, H, and Q during unilateral stance on the lax limb. These results suggest that a capsular-hamstring reflex is integrated into the existing structure of a preprogrammed postural synergy in order to compensate for ligamentous laxity. Furthermore, the generalized increase of response gain observed during perturbations of unilateral stance on the lax limb indicates that joint afference can modulate central programming to control localized joint hypermobility. A concept of postural control is discussed with respect to the capsular reflex, joint loading and displacement of the center of gravity.

Tongue-Based Biofeedback for Balance in Stroke: Results of an 8-Week Pilot Study

OBJECTIVE To assess balance recovery and quality of life after tongue-placed electrotactile biofeedback training in patients with stroke. DESIGN Prospective multicenter research design. SETTING Outpatient rehabilitation clinics. PARTICIPANTS Patients (N=29) with chronic stroke. INTERVENTIONS Patients were administered 1 week of therapy plus 7 weeks of home exercise using a novel tongue based biofeedback balance device. MAIN OUTCOME MEASURES The Berg Balance Scale (BBS), Timed Up and Go (TUG), Activities-Specific Balance Confidence (ABC) Scale, Dynamic Gait Index (DGI), and Stroke Impact Scale (SIS) were performed before and after the intervention on all subjects. RESULTS There were statistically and clinically significant improvements from baseline to posttest in results for the BBS, DGI, TUG, ABC Scale, and some SIS domains (Mobility, Activities of Daily Living/Instrumental Activities of Daily Living, Social, Physical, Recovery domains). Average BBS score increased from 35.9 to 41.6 (P<.001), and DGI score, from 11.1 to 13.7 (P<.001). Time to complete the TUG decreased from 24.7 to 20.7 seconds (P=.002). Including the BBS, DGI, TUG, and ABC Scale, 27 subjects improved beyond the minimal detectable change with 95% certainty (MDC-95) or minimal clinically important difference (MCID) in at least 1 outcome and 3 subjects improved beyond the MDC-95 or MCID in all outcomes. CONCLUSIONS Electrotactile biofeedback seems to be a promising integrative method to balance training. A future randomized controlled study is needed.

Influence of local sensory afference in the calibration of human balance responses

SummaryPeripheral sensory modulation of balance behavior may require a “calibrated” mechanism which would maintain upright standing by a feedback control of torque at the ankle joint. The calibration of human balance was studied using a systematic presentation of perturbation excursions and velocities in normal freely standing subjects. All perturbations (posterior movements of a force platform) induced a forward body sway and were presented by first increasing and then decreasing the magnitude of perturbation. In preselected conditions the stability of the ankle and hence the accuracy of surface orientation inputs was altered using a foam base placed under the subjects feet. Each subject pressed a hand held response key at the moment a postural disturbance was detected. The automatic neuromuscular response (ANR) was recorded from the gastrocnemius muscles bilaterally and the perturbation detection time (DT) was obtained from the onset of thenar muscle discharge. The major findings in this study were: (1) Conscious DT changed as a function of step variations in perturbation excursion and was disassociated from the ANR latency. The ANR latency remained essentially constant in all conditions and did not have any influence on the kinematics of body sway. (2) Normalized peak body sway decreased during unstable ankle conditions and the reduction of body sway could be attributed to an increase in the gain of the ANR across a 200 ms integration period. The ANR 200 ms amplitude also showed higher correlations with perturbation magnitude during unstable (versus stable) ankle conditions. (3) The 200 ms gastrocnemius amplitude was modulated by excursion and velocity of platform displacement but the amplitude integrated over 100 ms was dependent on only the velocity of perturbation. Our results indicate that balance is controlled by a centrally initiated postural response but regulated in amplitude by local sensory information. These results establish that the gain of the ANR is functional, peripherally driven, and occurs subconsciously to alter the kinematics of body sway.

Influence of Acuity on Physical Therapy Outcomes for Patients With Cervical Disorders

OBJECTIVES To assess the influence of symptom acuity on functional outcomes, pain, and patient perception of recovery after a physical therapy (PT) program for cervical disorders and to determine what variables are associated with patient function at discharge. DESIGN Retrospective case series. SETTING Outpatient settings at a tertiary care facility. PARTICIPANTS Patients (N=220) who were seen for PT between June 2003 and November 2005. INTERVENTIONS A customized rehabilitation program was developed for each patient based on examination findings and included a combination of the following interventions: mobilization or manipulation, flexibility exercises, strengthening exercises, endurance exercises, massage techniques, and heat and cold modalities. MAIN OUTCOME MEASURES Functional outcome, functional improvement, perceived pain, and perceived improvement scores in the CareConnections Outcomes System (formerly TAOS) database. RESULTS Persons whose symptom duration was greater than 6 months (chronic group) had significantly less functional improvement than persons whose symptom duration was less than 1 month (acute group). The median percentage improvement score for patient perceived recovery was also significantly lower for the chronic group than for the acute group. There was no significant difference in the percentage decrease in pain among the acute, subacute (symptom duration, 1-6 mo), and chronic groups. In regression analyses, a model with age (P=.001), symptom duration (P=.05), and inclusion of mobilization and manipulation interventions (P=.02) fit the data well and explained 35.6% of the variance in functional outcome score for all 3 groups combined. CONCLUSIONS Patients showed improvements in function after a rehabilitation program for cervical disorders. Patient functional score at discharge is influenced by age, symptom duration, and inclusion of mobilization or manipulation treatments.

Reliability of postural response as a function of muscular synergisms: Effect of supraspinal lesions

Abstract The characteristics of muscle discharge were evaluated for a non-choice reaction time postural task. Five normal and four hemiplegic subjects were required to match the height of a target trace representing 50% of total body weight by swaying on a force plate in a predetermined direction. The number of default response for hemiplegics (trials with no muscle discharge) was significantly higher than normal and the nature of muscle discharge was tonic rather than phasic. As the number of trial repetitions increased, postural reaction time showed a tendency to decrease for normals and increase for hemiplegics. We have proposed that the reliability and phase quality of muscle discharge following target appearance was directly proportional to the degree of muscle preprogramming. In this regard, patients with supraspinal lesions could not fully integrate automatic components of postural sway and instead relied on conscious intervention to maintain balance.

De relatie tussen sensorische organisatie en evenwichtsfunctie bij patiënten met een hemiplegie

Bij tien patienten met een hemiplegie werd het evenwicht in stand en tijdens het op dynamische wijze verplaatsen van het gewicht getest. Hiervoor werd de balanstest voor de sensorische organisatie (sot) gebruikt, samen met de sensomotorische test volgens Fugl-Meyer (fmst). De sot is een evenwichtstest met de tijd als een belangrijke factor en waarbij de somatosensorische, visuele en vestibulaire invloed op het handhaven van een verticale positie wordt nagegaan. De fmst is een test van de functionele status van een patient, waarbij duidelijk wordt hoeveel hulp nodig is tijdens de verschillende evenwichtstests en hoe lang de patient de test volhoudt.