Energy expenditure and activity of transfemoral amputees using mechanical and microprocessor-controlled prosthetic knees.

OBJECTIVE: To quantify the energy efficiency of locomotion and free-living physical activity energy expenditure of transfemoral amputees using a mechanical and microprocessor-controlled prosthetic knee. DESIGN: Repeated-measures design to evaluate comparative functional outcomes. SETTING: Exercise physiology laboratory and community free-living environment. PARTICIPANTS: Subjects (N=15; 12 men, 3 women; age, 42+/-9 y; range, 26-57 y) with transfemoral amputation. INTERVENTION: Research participants were long-term users of a mechanical prosthesis (20+/-10 y as an amputee; range, 3-36 y). They were fitted with a microprocessor-controlled knee prosthesis and allowed to acclimate (mean time, 18+/-8 wk) before being retested. MAIN OUTCOME MEASURES: Objective measurements of energy efficiency and total daily energy expenditure were obtained. The Prosthetic Evaluation Questionnaire was used to gather subjective feedback from the participants. RESULTS: Subjects demonstrated significantly increased physical activity-related energy expenditure levels in the participant's free-living environment (P=.04) after wearing the microprocessor-controlled prosthetic knee joint. There was no significant difference in the energy efficiency of walking (P=.34). When using the microprocessor-controlled knee, the subjects expressed increased satisfaction in their daily lives (P=.02). CONCLUSIONS: People ambulating with a microprocessor-controlled knee significantly increased their physical activity during daily life, outside the laboratory setting, and expressed an increased quality of life.

Does walking in a virtual environment induce unstable gait? An examination of vertical ground reaction forces.

Virtual reality (VR) can induce postural instability in standing and walking, as quantified with kinematic parameters. This study examines the effect of a VR environment on kinetic gait parameters. Ten healthy volunteers walked on an instrumented treadmill in a VR environment and a non-VR environment. In the VR environment, a corridor with colored vertical stripes comprising the walls was projected onto a concave screen placed in front of the treadmill. The speed of the moving image was perceptually equivalent to the speed of the treadmill, creating an illusion that subjects walked through the corridor. Vertical ground reaction forces were sampled. Kinetic parameters that reflect gait stability (weight acceptance peak force, weight acceptance rate, push-off peak force and push-off rate) were compared between the VR and non-VR environments. Subjects walked in the VR environment with increased magnitudes and rates of weight acceptance force and with increased rates of push-off force. Variability in weight acceptance rates and peak forces, and variability in push-off peak forces, were also increased in the VR environment. The gait deviations reflect a compensatory response to visual stimulation that occurs in the VR environment, suggesting that walking in a VR environment may induce gait instability in healthy subjects.

Hearing loss in rheumatoid arthritis.

OBJECTIVE: The objective of this study was to evaluate whether patients with rheumatoid arthritis (RA) are more likely to have subclinical hearing loss compared with persons without RA. METHODS: This is a case-control cross-sectional study of 29 patients with RA with disease duration greater than 5 years. Five males and five females were recruited into each decade category (age 40-49, 50-59, and 60-69). These cases were matched in a 1:1 ratio by sex and age to 30 control subjects. A comprehensive set of audiometric and disease severity assessments were performed. RESULTS: Seventeen (59%) of 29 patients with RA had abnormal hearing for at least one frequency (four in one ear, 13 in two ears) by audiometry as did 14 (47%) of 30 control subjects (five in one ear, nine in two ears). The percentage of patients with hearing loss (% RA vs. % control subjects) was: 45% versus 40% sensorineural, 10% versus 7% conductive, and 3% versus 0% mixed hearing loss. In RA versus control subjects, acoustic reflex threshold was abnormal in 17% versus 7%; speech reception threshold was abnormal in 10% versus 3%. Tympanometry and otoacoustic emission findings were similar in both groups. Word recognition did not differ between patients with RA and control subjects. In patients with RA/control subjects, hearing handicap, dizziness, and health assessment questionnaires were abnormal in 28%/7%, 14%/3%, and 72%/7%, respectively. CONCLUSION: There was no difference found in objective audiometric measurements in patients with RA compared with non-RA control subjects. Subjectively patients with RA were more likely to perceive themselves as having hearing disturbances, which may be related to overall disease related functional impairment.

Spatiotemporal gait deviations in a virtual reality environment.

Previous research suggests that postural sway in standing increases in virtual reality (VR) environments. This study was conducted to examine whether gait instability is prevalent when people walk in a VR environment. Ten healthy adults participated in the study. Subjects walked on a treadmill in a VR environment and a non-VR environment at each of three walking speeds: 0.9, 1.1, and 1.3 m/s. In the VR environment, an endless corridor with colored vertical stripes comprising the walls was projected onto a hemispherical screen placed in front of the treadmill. The speed of the moving corridor image was matched to the speed of the treadmill to create the illusion that subjects were walking through the endless corridor. Spatiotemporal data during gait were collected with an instrumented treadmill housing two piezoelectric force platforms. Gait parameters reflective of gait instability (stride length, step width, variability in stride velocity, and variability in step width) were compared between the VR and non-VR environments. Subjects walked in the VR environment with reduced stride lengths (p = 0.001), increased step widths (p = 0.001), and with increased variability in stride velocity (p < 0.001) and step width (p = 0.002). The gait deviations suggest that walking in a VR environment may induce gait instability in healthy subjects.

Comparison of subjective and objective measurements of balance disorders following traumatic brain injury.

Patients with mild traumatic brain injury (TBI) often complain of dizziness. However, these problems may be undetected by a clinical exam. Therefore, the purpose of this study was to evaluate the relationships between the subjective and objective measures of balance impairment. Ten patients with TBI (6 men and 4 women) and 10 matched controls participated in this study. Average duration since the TBI was 2.8 years (range 0.4-14.4). Six of the 10 subjects with TBI had abnormal imaging studies. All subjects and controls had a normal neuromuscular exam. Tinetti Balance Assessments were obtained and the TBI group was not significantly different from the control group. The Dizziness Handicap Inventory (DHI) score supported their complaints of "unsteadiness" and "imbalance" from the subjects with TBI. The DHI score was 32 +/- 23 (range 4-68) out of a maximum possible score of 100. Balance was tested using computerized dynamic posturography. The Sensory Organization Test score was significantly lower for subjects who had a TBI (70 +/- 12) compared to the control subjects (80 +/- 8), which indicated that the subjects with TBI had poorer balance than the control subjects. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole body center of mass (COM) while walking on a level surface. The subjects with TBI had significantly less displacement in the anterior/posterior direction, walked significantly slower, had significantly greater medial/lateral sway and velocity than the normal controls, and had significantly greater medial/lateral imbalance. There was a significant relationship between the physical aspects of the DHI and posturography. There was also significant relationship between the physical, functional, and total DHI and the motion of the COM. Overall, the motion of the COM predicted between 42 and 69% of the DHI score. The present study has demonstrated that objective measurements can quantify the patient's functional deficits. Therefore, these objective measurement techniques should be used to assess the clinical complaints of imbalance from patients with TBI.

Significant reduction in risk of falls and back pain in osteoporotic-kyphotic women through a Spinal Proprioceptive Extension Exercise Dynamic (SPEED) program.

OBJECTIVE: To determine the outcome of intervention with a spinal weighted kypho-orthosis (WKO) and a spinal proprioceptive extension exercise dynamic (SPEED) program on the risk of falls in ambulatory community-dwelling persons older than 60 years with osteoporosis-kyphosis at risk for falls. SUBJECTS AND METHODS: The study had 3 stages. At stage 1 (baseline), the 12 women in the kyphotic group were compared with 13 healthy controls to assess the risk of falls and balance disorder in the kyphotic group. At stage 2, the 12 kyphotic women began the SPEED program with a WKO (2 supervised sessions in an outpatient clinic and a 4-week, daily home-based training program). At stage 3, baseline and follow-up data of the kyphotic group were compared to determine the effect of intervention. RESULTS: At baseline, there were significant differences between the osteoporotic-kyphotic group and the control group in balance (P=.002), gait (P<.05), and strength (P<.05). After a 4-week intervention, comparison of the kyphotic group's baseline and follow-up results showed a significant change in balance (P=.003) and several gait parameters (P<.05). Mean back extensor strength improved significantly from baseline (144.0-46.5 N) to follow-up (198.6+/-55.2 N; P<.001). Lower extremity muscle strength was not changed significantly, except for improved left ankle plantar flexors (P=.02). Back pain decreased significantly (P=.001). CONCLUSION: Balance, gait, and risk of falls improved significantly with the 4-week SPEED program.

Balance disorder and increased risk of falls in osteoporosis and kyphosis: significance of kyphotic posture and muscle strength.

This controlled trial was designed to investigate the influence of osteoporosis-related kyphosis (O-K) on falls. Twelve community-dwelling women with O-K (Cobb angle, 50-65 degrees measured from spine radiographs) and 13 healthy women serving as controls were enrolled. Mean age of the O-K group was 76 years (+/-5.1), height 158 cm (+/-5), and weight 61 kg (+/-7.9), and mean age of the control group was 71 years (+/-4.6), height 161 cm (+/-3.8), and weight 66 kg (+/-11.7). Quantitative isometric strength data were collected. Gait was monitored during unobstructed level walking and during stepping over an obstacle of four different heights randomly assigned (2.5%, 5%, 10%, and 15% of the subject's height). Balance was objectively assessed with computerized dynamic posturography consisting of the sensory organization test. Back extensor strength, grip strength, and all lower extremity muscle groups were significantly weaker in the O-K group than the control group (P <0.05), except right ankle plantar flexors (P =0.09). There was a significant difference in the anteroposterior and mediolateral displacements and velocities. The O-K subjects had less anteroposterior displacement, greater mediolateral displacement, reduced anteroposterior velocity, and increased mediolateral velocity compared with controls for all conditions of unobstructed and obstructed level walking. Obstacle height had a significant effect on all center-of-mass variables. The O-K subjects had significantly greater balance abnormalities on computerized dynamic posturography than the control group (P =0.002). Data show that thoracic hyperkyphosis on a background of reduced muscle strength plays an important role in increasing body sway, gait unsteadiness, and risk of falls in osteoporosis.

Dynamic instability during obstacle crossing following traumatic brain injury.

Patients with traumatic brain injury (TBI) complain of "imbalance" or "unsteadiness" while walking, despite a normal gait on clinical examination. Thus, the purpose of this study was to determine if it was possible to quantitatively assess dynamic stability that did not have an obvious neuromuscular origin in individuals following TBI. Ten patients with documented TBI and 10 age, gender, and stature-matched healthy individuals participated in the study. All subjects were instructed to perform unobstructed level walking and to step over obstacles corresponding to 2.5%, 5%, 10%, and 15% of their height. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole body center of mass (COM). Subjects with TBI walked with a significantly slower gait speed and shorter stride length than their matched controls. Furthermore, subjects with TBI displayed a significantly greater and faster medio-lateral (M-L) COM motion and maintained a significantly greater M-L separation distance between their COM and center of pressure (COP) than their matched control subjects. These measurements indicate that subjects with TBI have difficulty maintaining dynamic stability in the frontal plane and have a reduced ability to successfully arrest their sagittal momentum. These findings provide an objective measurement that reflects the complaints of instability not observable on clinical examination for individuals who have suffered a TBI. This ability to identify any functional impairment after a traumatic brain injury that may affect patient safety is critical for prevention of re-injury during the recovery period.

Vestibular toxicity due to inhaled tobramycin in a patient with renal insufficiency.

Inhaled tobramycin is being used increasingly in patients with cystic fibrosis and other forms of bronchiectasis for treatment of bronchial colonization with Pseudomonas aeruginosa. The goal of inhaled antibiotics is to provide maximal concentrations at the site of infection without risking systemic toxicity. We report an unusual case of reversible vestibular toxicity due to inhaled tobramycin in a patient with renal failure who was undergoing hemodialysis. Although systemic absorption after inhaled tobramycin is reportedly negligible, no recommendations have been published regarding monitoring of serum concentrations in patients receiving this form of therapy. We suggest that clinicians consider monitoring serum concentrations of tobramycin in patients at risk of renal toxicity and/or ototoxicity, such as those with predisposing renal or otologic compromise. Further studies in at-risk patients are needed to determine the optimal frequency and timing of such monitoring.

Clinical experience with the vestibular evoked myogenic potential.

The vestibular evoked myogenic potential (VEMP) is a promising test of the descending vestibulocollic system. Our aim was to determine whether the VEMP can be applied to an older patient population and can detect lesions in descending vestibulospinal pathways. We also compared VEMP clinical performance with that of the standard caloric test. VEMP test performance was retrospectively analyzed in relation to clinical diagnosis and other vestibular test performance in 62 patients (age, 30-85 years) referred for vestibular testing to Mayo Clinic, Jacksonville, Florida. The VEMP was evoked using a 250 Hz tone burst. Results suggest age-related changes in VEMP amplitude and latency in this patient population. VEMP tests were sensitive to lesions not detected by electronystagmography. VEMP and caloric sensitivity and specificity were essentially equal (d' = 1). Combining both tests improved sensitivity. However, VEMP false-positive rates hampered specificity. VEMP testing may be refined to improve false-positive rates and clinical utility.

Medio-lateral motion of the center of mass during obstacle crossing distinguishes elderly individuals with imbalance.

This study was performed to investigate whether elderly patients with imbalance can be distinguished from healthy elderly subjects by comparing their whole body center of mass (COM) motion in the medio-lateral (M-L) direction during obstacle crossing. Nine healthy elderly adults and six elderly patients having complaints of 'dizziness' or 'unsteadiness' during walking (three with bilateral/unilateral vestibular weakness and three with unclear diagnosis) were recruited to perform unobstructed level walking and crossing of obstacles set to 2.5, 5, 10 and 15% of each subject's height. Kinematics of the COM was calculated using a weighted sum average of a 13-segment biomechanical model. There were no significant group differences for the temporal-distance gait parameters during all testing conditions. However, elderly patients with balance disorders demonstrated significantly greater and faster lateral motion of the COM when crossing over obstacles. These measurements distinguish elderly patients with imbalance from healthy elderly subjects. Furthermore, the increased M-L motion of the COM during obstacle crossing showed a positive correlation with an increased M-L range of motion of the swing foot trajectory. This increase in M-L motion indicates a compensatory adjustment in the swing foot trajectory to land the swing foot at an appropriate location that would establish a new base of support to counter the balance disturbance in the frontal plane.

An assessment of gait and balance deficits after traumatic brain injury.

OBJECTIVE: To assess the sensations of instability that many patients report after traumatic brain injury (TBI). DESIGN: A controlled study. SETTING: A motion analysis and vestibular and balance laboratory. PARTICIPANTS: Twenty subjects, 10 with TBI and complaints of instability, and 10 without TBI. INTERVENTIONS: Balance and gait analysis. MAIN OUTCOME MEASURES: Dizziness Handicap Inventory (DHI), caloric irrigation, optokinetic testing, Dix-Hallpike Test, posturography, and center of mass (COM) movement. RESULTS: Subjects were well matched in terms of age, height, weight, and gender. DHI scores of those with and without TBI differed significantly (32.2+/-23.0 vs 0.2+/-0.63, P<.001). Caloric and optokinetic circularvection testing were abnormal only in subjects with TBI (8/10 and 4/10, respectively). Benign paroxysmal positioning vertigo was present in only 3 subjects with TBI, and this either resolved spontaneously (n=1) or was successfully treated (n=2). Composite posturography scores of those with and without TBI differed significantly (69.6+/-35.8 vs 79.5+/-40.5, P=.02). Gait parameters also differed significantly between the groups (P=.05), with the subjects with TBI having lower anterior and posterior and higher medial and lateral COM displacements and velocities. CONCLUSIONS: Patients' complaints of instability after TBI may have objective correlates and may be rectifiable. Balance and gait testing in these patients is warranted.

Rotatory nystagmus synchronous with heartbeat: a treatable form of nystagmus.

PURPOSE: To describe a treatable form of nystagmus. METHODS: Two patients recently evaluated at the Mayo Clinic had experienced various forms of oscillopsia, imbalance, and worsening symptoms with a Valsalva maneuver. Close inspection of the eye revealed a subtle rotatory nystagmus that was synchronous with the heartbeat. RESULTS: The two patients had surgical treatment for dehiscence of the superior semicircular canal; postoperatively, their symptoms completely resolved. This is a relatively newly discovered condition that has not been described on either slit-lamp or ophthalmoscopic examination. The cause is related to a dehiscence of the superior semicircular canal that permits communication of variable pressures between the intracranial cavity and the perilymphatic spaces of the semicircular canal. CONCLUSION: Being aware of this unusual form of nystagmus may permit physicians to diagnose it--one of the few treatable forms of nystagmus.

Muscle activation patterns in subjects with and without low back pain.

OBJECTIVE: To analyze muscle activation patterns during various footplate perturbations, used as proprioceptive challenges in patients with low back pain (LBP) and in controls. DESIGN: A prospective and controlled comparative study. SETTING: Outpatient clinic. PARTICIPANTS: Twenty subjects with chronic LBP and 20 age- and sex-matched controls. INTERVENTIONS: The subjects underwent 5 sets of footplate perturbations in 3 directions with 16 perturbations for each set. MAIN OUTCOME MEASURES: Latency, frequency, and asymmetry of muscle activation of the erector spinae, rectus abdominus, anterior tibialis, and gastrocnemius muscles were measured bilaterally with surface electromyography. RESULTS: In the toes-up movements, subjects with LBP were significantly less likely to activate their rectus abdominus muscles (P=.02), and they were more likely to exhibit asymmetric muscle activation in the smaller forward movements (odds ratio=4.1, P=.03). The latter result appears to be driven by asymmetric contraction of the erector spinae and rectus abdominus. CONCLUSIONS: Significantly more subjects with LBP than control subjects exhibited absent firing of trunk muscles during 2 of the 5 footplate perturbations. These results suggest an abnormality of the neuromuscular loop and may represent altered proprioception.