Flurin Honegger

Trunk sway measures of postural stability during clinical balance tests : effects of a unilateral vestibular deficit

This research evaluated whether quantified measures of trunk sway during clinical balance tasks are sensitive enough to identify a balance disorder and possibly specific enough to distinguish between different types of balance disorder. We used a light-weight, easy to attach, body-worn apparatus to measure trunk angular velocities in the roll and pitch planes during a number of stance and gait tasks similar to those of the Tinetti and CTSIB protocols. The tasks included standing on one or two legs both eyes-open and closed on a foam or firm support-surface, walking eight tandem steps, walking five steps while horizontally rotating or pitching the head, walking over low barriers, and up and down stairs. Tasks were sought, which when quantified might provide optimal screening for a balance pathology by comparing the test results of 15 patients with a well defined acute balance deficit (sudden unilateral vestibular loss (UVL)) with those of 26 patients with less severe chronic balance problems caused by a cerebellar-pontine-angle-tumour (CPAT) prior to surgery, and with those of 88 age- and sex-matched healthy subjects. The UVL patients demonstrated significantly greater than normal trunk sway for all two-legged stance tasks especially those performed with eyes closed on a foam support surface. Sway was also greater for walking while rotating or pitching the head, and for walking eight tandem steps on a foam support surface. Interestingly, the patients could perform gait tasks such as walking over barriers almost normally, however took longer. CPAT patients had trunk sway values intermediate between those of UVL patients and normals. A combination of trunk sway amplitude measurements (roll angle and pitch velocity) from the stance tasks of standing on two legs eyes closed on a foam support, standing eyes open on a normal support surface, as well as from the gait tasks of walking five steps while rotating, or pitching the head, and walking eight tandem steps on foam permitted a 97% correct recognition of a normal subject and a 93% correct recognition of an acute vestibular loss patient. Just over 50% of CPAT patients could be classified into a group with intermediate balance deficits, the rest were classified as normal. Our results indicate that measuring trunk sway in the form of roll angle and pitch angular velocity during five simple clinical tests of equilibrium, four of which probe both stance and gait control under more difficult sensory conditions, can reliably and quantitatively distinguish patients with a well defined balance deficit from healthy controls. Further, refinement of these trunk sway measuring techniques may be required if functions such as preliminary diagnosis rather than screening are to be attempted.

Trunk Sway Measures of Postural Stability During Clinical Balance Tests in Patients With Chronic Whiplash Injury Symptoms

Study Design. Trunk sway occurring during clinical stance and gait tasks was compared between a group of subjects with a chronic whiplash injury, resulting from an automobile collision, and a normal collective. Objectives. To examine if population specific trunk sway patterns for stance and gait could be identified for chronic whiplash injury patients. Summary of Background Data. Our previous work has established that it is possible to identify specific patterns of stance and gait deficits for vestibular loss (both acute and compensated) patients and those with Parkinson’s disease. Our question was whether it was possible to use the same stance and gait tasks to identify patterns of trunk sway differences with respect to those of healthy subjects and individuals with a chronic whiplash injury. Methods. Twenty-five subjects with history of whiplash injury and 170 healthy age-matched control subjects participated in the study. Trunk sway angular displacements in chronic whiplash patients were assessed for a number of stance and gait tasks similar to those of the Tinetti and Clinical Test of Sensory Interaction and Balance (CTSIB) protocols. We used a lightweight, easy-to-attach, body-worn apparatus to measure trunk angular displacements and velocities in the roll (lateral) and the pitch (forward-backward) planes. Results. Data analysis revealed several significant differences between the two groups. A pattern could be identified, showing greater trunk sway for stance tasks and for complex gait tasks that required task-specific gaze control such as walking up and down stairs. Trunk sway was less, however, for simple gait tasks that demanded large head movements but no task-specific gaze control, such as walking while rotating the head. Conclusions. Subjects who have a chronic whiplash injury show a characteristic pattern of trunk sway that is different from that of other patient groups with balance disorders. Balance was most unstable during gait involving task-specific head movements which possibly enhance a pathologic vestibulo-cervical interaction.

Identifying deficits in balance control following vestibular or proprioceptive loss using posturographic analysis of stance tasks

OBJECTIVE To distinguish between normal and deficient balance control due to vestibular loss (VL) or proprioceptive loss (PL) using pelvis and shoulder sway measures. METHODS Body-worn gyroscopes measured pelvis and shoulder sway in pitch (anterior-posterior) and roll (side-to-side) directions in 6 VL, 6 PL and 26 control subjects during 4 stance tasks. Sway amplitudes were compared between groups, and were used to select optimal measures that could distinguish between these groups. RESULTS VL and PL patients had greater sway amplitudes than controls when standing on foam with eyes closed. PL patients also swayed more when standing with eyes closed on firm support and eyes open on foam. Standard sensory analysis techniques only differentiated VL patients from controls. Stepwise discriminate analysis showed that differentiation required pitch measures for VL patients, roll measures for PL patients, and both measures for all three groups. Pelvis measures yielded better discrimination than shoulder measures. CONCLUSIONS Distinguishing between normal and deficient balance control due to VL or PL required pitch and roll pelvis sway measures. SIGNIFICANCE Accurate identification of balance deficits due to VL or PL may be useful in clinical practice as a functional diagnostic tool or to monitor balance improvements in VL or PL patients.

Influence of virtual reality on postural stability during movements of quiet stance

INTRODUCTION Balance problems during virtual reality (VR) have been mentioned in the literature but seldom investigated despite the increased use of VR systems as a training or rehabilitation tool. We examined the influence of VR on body sway under different stance conditions. METHODS Seventeen young subjects performed four tasks (standing with feet close together or tandem stance on firm and foam surfaces for 60s) under three visual conditions: eyes open without VR, eyes closed, or while viewing a virtual reality scene which moved with body movements. Angular velocity transducers mounted on the shoulder provided measures of body sway in the roll and pitch plane. RESULTS VR caused increased pitch and roll angles and angular velocities compared to EO. The effects of VR were, for the most part, indistinguishable from eyes closed conditions. Use of a foam surface increased sway compared to a firm surface under eyes closed and VR conditions. CONCLUSION During the movements of quiet stance, VR causes an increase in postural sway in amplitude similar to that caused by closing the eyes. This increased sway was present irrespective of stance surface, but was greatest on foam.

Vestibular and proprioceptive influences on trunk movements during quiet standing

We characterized upper trunk and pelvis motion in normal subjects and in subjects with vestibular or proprioceptive loss, to document upper body movement modes in the pitch and roll planes during quiet stance. Six bilateral vestibular loss (VL), six bilateral lower-leg proprioceptive loss (PL) and 28 healthy subjects performed four stance tasks: standing on firm or foam surface with eyes open or closed. Motion of the upper body was measured using two pairs of body-worn gyroscopes, one mounted at the pelvis and the other pair at the shoulders. Pitch and roll angular velocities recorded from the gyroscopes were analyzed separately for low-frequency (<0.7 Hz) and high-frequency (>3 Hz) motion. Low-frequency pitch motion was similar for all groups, consisting of in-phase pelvis and shoulder motion. High-frequency pitch motion in controls and VL subjects was dominated by pelvis motion with little shoulder motion, but vice versa in PL subjects. Low-frequency roll motion changed for all groups from mainly shoulder and little pelvis motion to in-phase pelvis and shoulder motion after moving from a firm to foam surface. In contrast, high-frequency roll motion changed from mainly shoulder motion to mainly pelvis motion with the change to a foam surface, except for PL subjects with eyes closed. Coherent low-frequency sway between pelvis and shoulder was only pronounced in VL patients. These results indicate that relative motion between the pelvis and shoulder depends on the support surface, the type of sensory loss, and whether the motion is in roll or pitch plane. Furthermore, relative motion between the pelvis and upper trunk is an integral part of movement modes used to control quiet stance. Vestibular loss patients showed very similar movement modes as controls, with larger amplitudes. Proprioceptive loss patients, however, used more shoulder motion and stabilized the pelvis for the high-frequency mode. We conclude that there is relative motion between the upper trunk and pelvis during quiet stance and suggest that it may contribute to balance control.

Vestibular and proprioceptive contributions to human balance corrections: aiding these with prosthetic feedback.

Movement strategies controlling quiet stance and rapid balance corrections may have common characteristics. We investigated this assumption for lower leg proprioceptive loss (PL), peripheral vestibular loss (VL), and healthy controls. Our underlying hypothesis was that changes in movement‐strategy modulation following sensory loss would improve with prosthetic biofeedback. Quiet stance was measured under different sensory conditions and compared to corrections induced by multidirection support‐surface tilts. Response synergies were assessed using electromyography recordings from several muscles. Biofeedback of trunk sway during gait and stance tasks used lower trunk rotations to drive head‐band‐mounted vibro‐tactile and auditory actuators. Strategies of quiet stance were different for roll and pitch, depending on sensory conditions. Simultaneously acting strategies were observed for low‐ and high‐frequency sway. PL induced strategies different from those of VL and controls. VL strategies were identical to those of controls but with greater amplitudes. Tilt perturbation movement strategies were similar to high‐frequency strategies of quiet stance—multisegmental. VL induced increased trunk pitch and roll responses with hypermetric trunk muscle responses and hypometric knee responses but unchanged synergies. Increasing PL up the legs caused changed synergies. Biofeedback reduced stance body sway in VL and elderly subjects. In conclusion, several movement strategies underlie quiet stance with high‐frequency strategies being common to those of perturbed stance. PL changes both movement strategies and synergies, whereas VL only causes pathological changes to the modulation depth. Thus, VL is more easily rectified using trunk sway positional biofeedback.

The effect of prosthetic feedback on the strategies and synergies used by vestibular loss subjects to control stance

BackgroundThis study investigated changes in stance movement strategies and muscle synergies when bilateral peripheral vestibular loss (BVL) subjects are provided feedback of pelvis sway angle.MethodsSix BVL (all male) and 7 age-matched male healthy control (HC) subjects performed 3 stance tasks: standing feet hip width apart, eyes closed, on a firm and foam surface, and eyes open on foam. Pelvis and upper trunk movements were recorded in the roll and pitch planes. Surface EMG was recorded from pairs of antagonistic muscles at the lower leg, trunk and upper arm. Subjects were first assessed without feedback. Then, they received training with vibrotactile, auditory, and fall-warning visual feedback during stance tasks before being reassessed with feedback.ResultsFeedback reduced pelvis sway angle displacements to values of HCs for all tasks. Movement strategies were reduced in amplitude but not otherwise changed by feedback. These strategies were not different from those of HCs before or after use of feedback. Low frequency motion was in-phase and high frequency motion anti-phasic. Feedback reduced amplitudes of EMG, activity ratios (synergies) of antagonistic muscle pairs and slightly reduced baseline muscle activity.ConclusionsThis is the first study demonstrating how vestibular loss subjects achieve a reduction of sway during stance with prosthetic feedback. Unchanged movement strategies with reduced amplitudes are achieved with improved antagonistic muscle synergies. This study suggests that both body movement and muscle measures could be explored when choosing feedback variables, feedback location, and patient groups for prosthetic devices which reduce sway of those with a tendency to fall.

Relation between head impulse tests, rotating chair tests, and stance and gait posturography after an acute unilateral peripheral vestibular deficit.

Background Vestibulo-ocular reflex (VOR) deficits and balance instability during stance and gait are typical for an acute unilateral peripheral vestibular deficit (AUPVD). The relation between different VOR measures with recovery is unknown, as is the relation of VOR measures to balance control. To answer these questions, we examined changes over time in caloric canal paresis (CP), head impulse tests (HIT), whole body rotation (ROT) tests of the horizontal VOR, and changes in trunk sway during stance and gait tests, for cases of presumed vestibular neuritis. Methods HIT was performed with short ca. 200 degrees per second head turns, ROT with triangular 24-second velocity profiles (peak 120 degrees per second, acceleration 20 degrees per second squared). To measure balance control, body-worn gyroscopes measured pitch (anterior-posterior) and roll (lateral) sway angles and angular velocities at lumbar 1 to 3. Results Changes during recover in ROT and HIT responses to the deficit side were equally well related (R = 0.8, p < 0.001) to changes in caloric CP values. ROT but not HIT responses to the normal side were also related to CP responses (R = 0.53, p = 0.02). Spontaneous nystagmus levels were related to changes instance balance control (R = 0.52, p = 0.001). Balance during gait improved over time but was not well correlated with changes in VOR measures (R = 0.26 max., p > 0.05). Conclusion Both HIT and ROT track VOR recovery on the deficit side due to central compensation and peripheral recovery. However, only ROT track changes in the central compensation of normal side responses. The weak correlations between VOR and stance and gait tests suggest that the latter should also be tested to judge the effect of an AUPVD on balance control.

Incorporating voluntary unilateral knee flexion into balance corrections elicited by multi-directional perturbations to stance.

Positive effects on lateral center of mass (CoM) shifts during balance recovery have been seen with voluntarily unilateral arm raising but not with voluntarily bilateral knee flexion. To determine whether unilateral voluntary knee movements can be effectively incorporated into balance corrections we perturbed the balance of 30 young healthy subjects using multi-directional rotations of the support surface while they simultaneously executed unilateral knee flexion. Combined pitch and roll rotations (7.5 degrees and 60 degrees/s) were presented randomly in six different directions. Subjects were tested in four stance conditions: balance perturbation only (PO); cued flexion of one knee only (KO); combined support surface rotation and cued (at rotation onset) flexion of the uphill knee, contralateral to tilt (CONT), or of the downhill knee, ipsilateral to tilt (IPS). Outcome measures were CoM motion and biomechanical and electromyography (EMG) responses of the legs, arms and trunk. Predicted measures (PO+KO) were compared with combined measures (CONT or IPS). Unilateral knee flexion of the uphill knee (CONT) provided considerable benefit in balance recovery. Subjects rotated their pelvis more to the uphill side than predicted. Downhill knee bending (IPS) also had a positive effect on CoM motion because of a greater than predicted simultaneous lateral shift of the pelvis uphill. KO leg muscle activity showed anticipatory postural activity (APA) with similar profiles to early balance correcting responses. Onsets of muscle responses and knee velocities were earlier for PO, CONT, and IPS compared to KO conditions. EMG response amplitudes for CONT and IPS conditions were generally not different from the PO condition and therefore smaller than predicted. Later stabilizing responses at 400 ms had activation amplitudes generally equal to those predicted from the PO+KO conditions. Our results suggest that because EMG patterns of anticipatory postural activity of voluntary unilateral knee flexion and early balance corrections have similar profiles, the CNS is easily able to incorporate voluntary activation associated with unilateral knee flexion into automatic postural responses. Furthermore, the effect on movement strategies appears to be non-linear. These findings may have important implications for the rehabilitation of balance deficits.

Cricothyroid joint anatomy as a predicting factor for success of cricoid-thyroid approximation in transwomen.

Cricoid‐thyroid approximation (CTA) performed to elevate the vocal pitch in transwomen fails in about one‐third of the patients. The purpose of this study was to test the feasibility of predicting the likelihood of success of CTA by preoperative determination of the crico‐thyroid joint (CTJ) type using three‐dimensional (3‐D) images derived from high‐resolution computer tomography (HRCT).