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Biomedical subjects

G F Harris

Publications and source records attributed to G F Harris.

At least 37 records · Page 2Linked to original sources
PubMed1994

Biomechanical and reflex responses to joint perturbations during electrical stimulation of muscle: instrumentation and measurement techniques.

A test device is developed to measure ankle joint compliance and muscle activity when the ankle is subjected to perturbations in angular position (or torque) from bias positions achieved volitionally or via electrical stimulation. The ankle measurement system uses a pivoting footplate and is operable with the subject sitting or supine. A companion platform for the knee is developed that uses a rotary arm and attached leg brace and is operable with the subject's leg in the horizontal or vertical plane. The knee fixture's pivoting arm can slide to account for the cam-like movement of the knee during rotation. The devices use similar hardware and share common instrumentation and control. Precise torque or position perturbations are delivered by a computer-controlled torque motor to the ankle or knee. Angular displacement, torque, acceleration, knee fixture moment arm and electromyographic data are collected on analogue tape and simultaneously digitised and stored. A special stimulator/recording amplifier permits the recording of electromyographic signals from the stimulated muscle. Experimental data indicate that the ankle and knee devices, operated horizontally, are purely inertial systems. Sample ankle and knee joint responses to perturbations are presented.

Ankle Joint↗
PubMed1994

Comparison of stability of proximal crescentic metatarsal osteotomy and proximal horizontal "V" osteotomy.

Proximal metatarsal osteotomies are often performed in patients with hallux valgus and significant metatarsus primus varus. The crescentic osteotomy is popular; however, some authors have reported malunion of the metatarsal shaft caused by dorsal angulation of the osteotomy in a significant number of cases. Recently, proximal transverse "V" osteotomies have been reported to have good results, with rapid healing and no dorsal malunions. We compared the stability of a transverse, proximal "V" osteotomy, using two 0.062-inch K-wires or a 3.5-mm cortical screw for fixation, with that of the proximal crescentic osteotomy, using a 3.5-mm cortical screw fixation. The three osteotomy/fixation techniques were performed on 30 fresh-frozen cadaver feet. The specimens were loaded to failure at the fixation site by applying a load through the plantar surface of the first metatarsal head. Force versus displacement curves were obtained to calculate the failure load and stiffness. Statistical differences among the three groups were determined by the nonparametric Mann-Whitney U-test and the standard t-test. The "V" osteotomy/screw group was more stable than either the "V" osteotomy/pin group or the crescentic osteotomy/screw group. Differences in failure strength between the "V"/screw group and the other two groups were significant at the P < .01 level and the differences in stiffness were significant at the P = .05 level. No statistical differences were found between the "V"/pins and the crescentic/screw groups.

Biomechanical Phenomena↗
PubMed1994

Multistep measurement of plantar pressure alterations using metatarsal pads.

Metatarsal pads are frequently prescribed for nonoperative management of metatarsalgia due to various etiologies. When appropriately placed, they are effective in reducing pressures under the metatarsal heads on the plantar surface of the foot. Despite the positive clinical reports that have been cited, there are no quantitative studies documenting the load redistribution effects of these pads during multiple step usage within the shoe environment. The objective of this study was to assess changes in plantar pressure metrics resulting from pad use. Ten normal adult male subjects were tested during a series of 400-step trials. Pressures were recorded from eight discrete plantar locations at the hindfoot, midfoot, and forefoot regions of the insole. Significant increases in peak pressures, contact durations, and pressure-time integrals were noted at the metatarsal shaft region with pad use (P < or = .05). Statistically significant changes in metric values were not seen at the other plantar locations, although metatarsal pad use resulted in mild decreases in mean peak pressures at the first and second metatarsal heads and slight increases laterally. Contact durations decreased at all metatarsal head locations, while pressure-time integrals decreased at the first, second, third, and fourth metatarsal heads. A slight increase in pressure-time integrals was seen at the fifth metatarsal head. The redistribution of plantar pressures tended to relate not only to the dimensions of the metatarsal pads, but also to foot size, anatomic foot configuration, and pad location. Knowledge of these parameters, along with careful control of pad dimensions and placement, allows use of the metatarsal pad as an effective orthotic device for redistributing forefoot plantar pressures.

Adult↗
PubMed1994

Procedures for gait analysis.

Observational gait analysis is clinically useful with videotape slow-motion replay and freeze-frame, offering significant improvement over unaided visual observation. Any form of observational gait analysis, however, has limited precision and is more descriptive than quantitative. This article reviews procedures that are available for gait analysis. Gait analysis systems have evolved from cine with manual digitization, electrogoniometry, and video technology to sophisticated automated tracking systems. When used in conjunction with biomechanical models, these systems allow quantitative analysis of many specific gait characteristics such as joint moments and powers (kinetic analysis), joint angles, angular velocities, and angular accelerations (kinematic analysis). Analysis of dynamic electromyographic activity and energy consumption adds useful clinical information to gait analysis. The combination of a careful clinical assessment and gait analysis can be a powerful tool for the clinician.

Biomechanical Phenomena↗
PubMed1993

Sensate and insensate in-shoe plantar pressures.

In the individual with loss of protective sensation, the presence of high plantar pressures has been considered a risk factor for the development of plantar ulceration. Previous studies of insensate plantar pressures have measured a limited number of isolated, barefoot steps in a laboratory setting. Such isolated snapshots of barefoot plantar pressures do not give us insight into possible step-to-step variations or what plantar pressures occur when wearing shoes. The purpose of this study was to quantitatively examine and compare in-shoe plantar pressures during continuous walking by normal sensate and diabetic insensate subjects. A portable, insole data-acquisition system was used for pressure measurement during 4 minutes of normal continuous walking. Seven pressure sensors were placed in each insole under posterior and anterior heels, the metatarsal heads, and hallux. Twelve sensate and five insensate subjects were studied. We found that the insensate group had higher plantar pressures under posterior and anterior heels and the first metatarsals compared with the sensate group. From the study of the coefficients of variation, we demonstrated a larger step-to-step variation in plantar pressures for the insensate during continuous walking, suggesting the need for caution in interpreting the data from isolated force plate steps when studying insensate individuals.

Adult↗
PubMed1993

A biomechanical impact test system for head and facial injury assessment and model development.

A biomechanical test system has been developed and validated to conduct controlled uniaxial impact experiments of head and facial trauma. The design reduces off-axis accelerations which are not in the direction of impact and allows accurate positioning of test specimens. Impact forces, displacement histories, impulses at impact and spectral responses are compared to free-fall test results at contact velocities representative of facial injuries (2.5, 3.1 and 3.8 m s-1). Models based on the experimental results are developed to reveal stiffness and inertial properties of impact for use in the design of biomechanically protective steering wheels, air bags and other potential impact structures. The results indicate that the system provides a flexible yet controllable method for positioning and testing impact structures reliably.

Accidents, Traffic↗
PubMed1993

Neuroelectric stimulation in cerebral palsy: long-term quantitative assessment.

Results from multiple tests including somatosensory evoked potentials, passive resistance to motion, upper extremity motor skills evaluation, neuromuscular examination, and parental interview were evaluated in 13 children with cerebral palsy (CP) who received chronic cerebellar stimulation (CCS) for reduction of spasticity and movement disorders during the past 14 years. The prospective study included immediate postoperative follow-up data as well as longer term results from the quantitative test series. Although CCS was effective in reducing hypertonicity in CP children during the immediate short-term, the diminishment waned significantly 3-5 years postoperatively.

Cerebral Palsy↗
PubMed1991

A microprocessor-based data-acquisition system for measuring plantar pressures from ambulatory subjects.

We have developed a portable microprocessor-based data-acquisition system to measure discrete plantar pressures within the shoe from ambulatory subjects. The system offers improved accuracy, repeatability, portability, and flexibility not available in current commercial systems. It consists of 14 conductive polymer pressure sensors, 14 analog amplifiers, an 8-bit analog-to-digital converter, a microprocessor, 120 kbytes of memory space, and a parallel I/O interface. Seven pressure sensors are embedded within each insole and located at the posterior heel, anterior heel, the four metatarsal heads, and hallux of each foot. The system is capable of continuously sampling 14 channels of pressure data for 7 min at a 20-Hz sample rate. The recorded data are downloaded into a microcomputer for further processing, analysis, and display. Foot pressures have been acquired from a sensate subject during multiple walking trials.

Diagnosis, Computer-Assisted↗
PubMed1991

Foot pressure distribution during walking and shuffling.

The insensate foot is vulnerable to tissue damage from areas of repetitive, excessive pressures. It has been previously stated that a shuffling gait with short steps would increase the period of foot flat and thus minimize any excessive local plantar pressures. This theory was quantitatively evaluated with a portable, in-shoe pressure data-acquisition system. Seven pressure sensors were located in the left and right insoles under the metatarsal heads, hallux, and posterior and anterior heels. Plantar pressure data were acquired from ten able-bodied subjects during four minutes of continuous shuffling and walking at a metronome-controlled cadence. Peak pressures, foot-to-floor contact durations, and pressure-time integrals under each sensor during shuffling and walking were analyzed and compared. Peak pressures were decreased at all sensor sites during a shuffling gait. The greatest decreases were noted at the first and second metatarsals (up to 57.8%) and hallux (up to 63.2%). A 41.6% decrease in overall summated peak plantar pressures during shuffling was found. Foot-to-floor contact durations during shuffling were increased from 22.0% to 76.9% at all 14 sensor locations. Pressure-time integrals during shuffling were increased at the heels (up to 78.9%) and decreased at the metatarsal heads and great toes (up to 26.7%). There was a 3.3% increase in the overall summated pressure-time integral during shuffling. Our findings are consistent with the hypothesis that a shuffling gait increases the period of foot flat and the area of weight bearing, resulting in lower peak plantar pressures on any one area.

Adult↗
PubMed1989

Analysis of neuroelectric implant integrity.

A 10-year follow-up study of neuroelectric implant integrity has been completed for 27 subjects who were treated for movement disorders associated with cerebral palsy. Data used for analysis included X-ray material, clinical data, and results from electrophysiological testing. Of the 21 subjects with subcutaneous receivers placed in the thoracic region, 81% experienced wire (67%) or receiver (14%) failure. Of the 6 subjects with subcutaneous receivers placed in the occipital region, there were no wire failures and one (17%) receiver failure. The occipital units lasted a minimum of 5.2 years without complications, whereas the thoracic units failed as early as 6 months after surgery, and lasted an average of 3.8 years. All wire fractures occurred between C1 and T1. Two types of fracture occurred, one consisting of a clean break and the other consisting of a scenario of bending and kinking, then thinning and fraying, and finally progressive multiple fragmentation. With a few exceptions the clean breaks occurred between C1 and C3, while the fraying scenario occurred between C6 and T1. Mechanisms for failure are discussed, as are results from material tests of wire samples.

Adolescent↗
PubMed1989

Posteromedial release for idiopathic talipes equinovarus. A long-term follow-up study.

Eighteen children with 26 idiopathic talipes equinovarus deformities were treated by postermedial release (PR) in the interval between 1975 and 1980 and investigated retrospectively. Evaluations included physical examination, functional evaluation, roentgenographic evaluation, and evaluation of foot track tracing pattern. The average follow-up period was 8.2 years. Thirty percent had had previous tendo Achilles lengthenings and 15% had had previous lengthenings plus posterior capsulotomies. Based on Turco's criteria, the results of PR were graded 38.9% excellent, 26.9% good, 15.6% fair, and 18.6% failure.

Achilles Tendon↗
PubMed1987

Thoracic suspension: quantitative effects upon seating pressure and posture.

Seating pressure in 10 subjects using a thoracic suspension orthosis was studied quantitatively. Anterior, posterior, and ischial pressures were measured bilaterally both unsuspended and during a 90 to 120 minute interval while suspended. Significant decreases in seating pressure were noted following suspension, with a mean decrease of 59.8%. Significant changes in lateral support were noted with suspension, as was a reduction in both the absolute pressure and relative distribution of pressure to the ischial areas. Relative redistribution of pressure in the anterior-posterior direction was related to leg support condition. All subjects who presented with pressure sores healed subsequent to thoracic suspension. Those with spinal curvature showed a 10 to 20 degree correction immediately following suspension. This correction generally was not maintained, however, in a temporal analysis. The data indicates that thoracic suspension can effectively reduce seating pressure and alter lateral posture, while leg support condition has a greater effect upon anterior-posterior pressure distribution. The use of a seat cushion to prevent subject swinging while suspended did not adversely affect the overall suspended pressures in this study, although the subjects without seat cushions showed lower overall suspended pressures.

Adolescent↗
PubMed1987

A multichannel PWM telemetry system for kinematic gait analysis.

A multichannel biotelemetry system using pulse-width modulation-frequency modulation (PWM-FM) is described in detail for laboratory construction. Its application in a kinematic gait-analysis system is demonstrated, employing minimally encumbering electrogoniometry and foot-contact switches. The triaxial electrogoniometers sense rotational joint motion, and four foot-switches under the sole of each foot provide information on placement and temporal contact. Signals from the multiple sensors are amplified, encoded by pulse-width modulation, and transmitted at an FM radio frequency of 107 MHz. Received data are decoded and then sampled by a minicomputer for analysis. Results from a comparative study of kinematic gait in five normal subjects and five children with cerebral palsy demonstrate system effectiveness in providing quantitative data and various intrasubject and intersubject gait differences. Factors reviewed in the analysis include swing and stance times; cadence; hip-joint motion in sagittal, coronal, and transverse planes; and sequence of foot placement.

Analog-Digital Conversion↗