Jacqueline J. Wertsch

Analysis of postural control synergies during quiet standing in healthy children and children with cerebral palsy

OBJECTIVE To estimate the contribution of body transverse rotation using weighted differential center of pressure signals during quiet standing in healthy children and in children with cerebral palsy. DESIGN Body sway was indirectly measured through center of pressure data, which was calculated using dual force platforms. BACKGROUND Assessment of postural control synergies using center of pressure data provides a unique method for center of mass data analysis in characterizing complex balance sway. METHODS Using dual force platforms, linear expressions for the coordinates of right and left center of pressure signals were developed to identify and characterize balance control synergies during quiet standing. Subjects were also tested during eyes open and eyes closed trials to determine the significance of visual input on these control synergies. RESULTS The limb protraction/retraction control was found to be dominant during medial-lateral sway, whereas the estimated body transverse rotation contribution was found to be more significant than the previously reported measures of anterior-posterior balance. These findings were consistent in healthy children and in children with cerebral palsy during both eyes open and eyes closed trials. CONCLUSION The weighted differential center of pressure signals show that the estimated body transverse rotation contribution is significant in healthy children and critical for postural stability in children with cerebral palsy. RELEVANCE This study identifies the significance of body transverse rotation control contribution in upright posture. Children with cerebral palsy with relatively poor ankle control demonstrate the importance of body transverse rotation for postural stability.

Effect of rocker soles on plantar pressures.

OBJECTIVE To examine the effect of different types of rocker soles on plantar pressures. DESIGN In-shoe plantar pressures were measured in subjects without deformity with baseline shoes and 3 types of rockers: toe-only, negative heel, and double. SETTING Medical college. PARTICIPANTS Forty healthy patients (20 men, 20 women) without foot deformity. INTERVENTIONS Plantar pressures were recorded over a 2 1/2-hour test period with over 400 steps analyzed for each type of rocker sole. Peak pressures, pressure-time integral (PTI), and sensor contact duration were computed for each step. MAIN OUTCOME MEASURES Peak plantar pressure PTI, and contact duration were compared for each rocker with a baseline shoe. RESULTS Significant reduction (P<.01) in peak pressure and PTI were recorded across the forefoot for all 3 rockers. The reduction of pressure at the forefoot was balanced by shifting pressure to the midfoot with the negative heel and toe-only rockers. CONCLUSION This study lends scientific credence to the prescription of rocker soles for patients who need forefoot pressure reduction, such as in diabetic neuropathy and possible ulceration.

Walking Cadence Effect on Plantar Pressures

OBJECTIVE Prior studies have examined the effect of cadence on ground reaction forces by use of a force plate. Force plate studies generally analyze isolated steps and do not provide insight into ongoing step-to-step variations or in-shoe plantar pressures. The objective of this study was to evaluate the effect of walking cadences on in-shoe plantar pressures over extended periods of continuous walking. DESIGN Nonrandomized control trial. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS Volunteer sample of 8 able-bodied subjects. INTERVENTIONS In-shoe plantar pressures were studied during four minutes of continuous walking at controlled cadences of 70, 80, 90, 100, 110, and 120steps/min. For each cadence more than 200 steps were analyzed for each of the 8 subjects. MAIN OUTCOME MEASURES Pressure-time integrals, foot-to-floor contact durations, and peak pressures at all 14 locations were processed for each step. Changes were calculated compared to values at 70steps/min. RESULTS With increasing cadence, mean pressure-time integrals continuously decreased (45% at 120steps/min); mean foot-to-floor contact durations continuously decreased (64% at 120steps/min); and mean peak pressures increased (119% at 120steps/min). CONCLUSIONS Our results show that as walking cadence increases, pressure-time integrals and foot-to-floor contact durations decrease, and peak plantar pressures increase. This is clinically relevant to all kinetic gait studies because our results suggest that normal values should be established for each cadence.

A portable insole plantar pressure measurement system

To analyze plantar pressures during activities of daily living, one needs a fully portable system capable of measuring many steps over extended periods. This paper presents an inexpensive, reliable, portable plantar pressure acquisition system which we have developed. It allows the long-term recording (up to 2 hours) of pressure-time data from 14 pressure sensors within insoles. The sensor chosen is an inexpensive, conductive polymer sensor that is only 0.25 mm thick yet able to withstand sudden overloads. The portable, battery-powered, microprocessor-based data acquisition system has a memory space of 480 kbytes for data storage. It can collect pressure data from 14 insole sensors at a 20 Hz sample frequency for 5 seconds every minute over a 2-hour period. It enables the long-term measurement of plantar pressures during normal activities in a natural unrestricted environment. The design and development of this portable insole plantar pressure measurement system is described.

The Strain Index (SI) and Threshold Limit Value (TLV) for Hand Activity Level (HAL): risk of carpal tunnel syndrome (CTS) in a prospective cohort.

A cohort of 536 workers was enrolled from 10 diverse manufacturing facilities and was followed monthly for six years. Job physical exposures were individually measured. Worker demographics, medical history, psychosocial factors, current musculoskeletal disorders (MSDs) and nerve conduction studies (NCS) were obtained. Point and lifetime prevalence of carpal tunnel syndrome (CTS) at baseline (symptoms + abnormal NCS) were 10.3% and 19.8%. During follow-up, there were 35 new CTS cases (left, right or both hands). Factors predicting development of CTS included: job physical exposure (American conference of governmental industrial hygienists Threshold Limit Value (ACGIH TLV) for Hand Activity Level (HAL) and the Strain Index (SI)), age, BMI, other MSDs, inflammatory arthritis, gardening outside of work and feelings of depression. In the adjusted models, the TLV for HAL and the SI were both significant per unit increase in exposure with hazard ratios (HR) increasing up to a maximum of 5.4 (p = 0.05) and 5.3 (p = 0.03), respectively; however, similar to other reports, both suggested lower risk at higher exposures. Data suggest that the TLV for HAL and the SI are useful metrics for estimating exposure to biomechanical stressors. Practitioner Summary: This study was conducted to determine how well the TLV for HAL and the SI predict risk of CTS using a prospective cohort design with survival analysis. Both the TLV for HAL and the SI were found to predict risk of CTS when adjusted for relevant covariates.

Instantaneous postural stability characterization using time-frequency analysis

Postural stability assessment is critical to a more accurate understanding of sway and balance control. The center of pressure (COP) metric has been shown to be a suitable output measure for time and frequency analysis. However, the center of pressure is a non-stationary signal. Standard time and frequency analysis methods may not be adequate for monitoring the dynamic changes in the center of pressure signal. In this study a time-frequency method, based on data-adaptive evolutionary spectral estimation, is applied to monitor the dynamic changes of the center of pressure in a non-stationary environment. Metrics including the instantaneous mean frequency (IMF), instantaneous spectral bandwidth (ISB), and instantaneous average power (IAP) are analyzed to characterize the center of pressure signal in both the anterior-posterior (AP) and the medial-lateral (ML) planes. Within the confines of this study, the IMF was found to be inversely proportional to IAP. The inverse proportionality factors were calculated in both eyes-open and eyes-closed trials during upright quiet standing. These findings suggest that the time-frequency analysis provides instantaneous metrics which describe the amplitude changes and frequency shift of the center of pressure under a variety of environmental conditions, thus providing a more reliable quantification of postural control.

An umbilical data-acquisition system for measuring pressures between the foot and shoe

An umbilical data-acquisition system has been developed for measuring pressure between the foot and shoe during walking. It consists of pressure sensors in the insoles of shoes, amplifier circuits, umbilical cables, a 12-b analog-to-digital converter, and a graphics display card in an IBM PC for real-time data collection and display. The applied pressure on a sensor decreases its resistance, which causes the output voltage of the amplifier circuit to increase. Seven sensors were attached to the surface of each insole of a pair of extra-depth shoes and calibrated in the insole before and after each test using a load cell as a reference. The IBM PC samples the outputs from the sensor and the load cell and stores a piecewise-linear lookup table for use in compensation for the nonlinearity of the sensor. On the PCs graphics display, two programs provide displays of foot pressures as real-time bar graphs or as analog pressure versus time curves.<<ETX>>

Capacitive sensors for measuring the pressure between the foot and shoe

A test was conducted of a Hercules Orthoflex capacitive sensor used to measure pressure distribution under the foot for gait analysis and sensory substitution. Maximal nonlinearity for the sensor is 16%, and maximal hysteresis is 10% over the pressure range 0 to 1.3 MPa. Seven transducers in each shoe determine the distribution of pressure.<<ETX>>

The WISTAH hand study: A prospective cohort study of distal upper extremity musculoskeletal disorders

BackgroundFew prospective cohort studies of distal upper extremity musculoskeletal disorders have been performed. Past studies have provided somewhat conflicting evidence for occupational risk factors and have largely reported data without adjustments for many personal and psychosocial factors.Methods/designA multi-center prospective cohort study was incepted to quantify risk factors for distal upper extremity musculoskeletal disorders and potentially develop improved methods for analyzing jobs. Disorders to analyze included carpal tunnel syndrome, lateral epicondylalgia, medial epicondylalgia, trigger digit, deQuervain’s stenosing tenosynovitis and other tendinoses. Workers have thus far been enrolled from 17 different employment settings in 3 diverse US states and performed widely varying work. At baseline, workers undergo laptop administered questionnaires, structured interviews, two standardized physical examinations and nerve conduction studies to ascertain demographic, medical history, psychosocial factors and current musculoskeletal disorders. All workers’ jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of musculoskeletal disorders. Repeat nerve conduction studies are performed for those with symptoms of tingling and numbness in the prior six months. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. Case definitions have been established. Point prevalence of carpal tunnel syndrome is a combination of paraesthesias in at least two median nerve-served digits plus an abnormal nerve conduction study at baseline. The lifetime cumulative incidence of carpal tunnel syndrome will also include those with a past history of carpal tunnel syndrome. Incident cases will exclude those with either a past history or prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression.DiscussionA prospective cohort study of distal upper extremity musculoskeletal disorders is underway and has successfully enrolled over 1,000 workers to date.

Effects of the toe-only rocker on gait kinematics and kinetics in able-bodied persons

Rocker sole shoes are commonly prescribed to diabetic patients with insensate feet. Recent passage of the therapeutic shoe bill has drawn an increased focus on prescription of rehabilitative footwear. The purpose of this work is to investigate the dynamics of lower extremity joints (hip, knee, and ankle) with the application of a toe-only rocker sole shoe under controlled laboratory conditions. Forty (40) normal adults volunteered for gait analysis using controlled baseline and prescription toe-only rocker sole shoes. Three-dimensional motion analysis techniques were used to acquire kinematic and kinetic data using a six camera Vicon 370 motion system and two AMTI force plates. While significant changes from baseline to toe-only rocker were noted in cadence (increased) and stride length (decreased), no significant change in walking speed was observed. The most significant kinematic changes with the application of the toe-only shoe occurred at the ankle and knee in the sagittal plane during stance. The most significant kinetic effects were observed in the hip and knee during swing phase. Changes in power were noted at all joints, mostly in terminal stance. These kinematic and kinetic changes, along with previously studied effects of pressure relief at the metatarsal heads, should aid medical professionals in prescribing prophylactic footwear.