An optoelectric plantar "shear" sensing transducer: design, validation, and preliminary subject tests

A prototype miniature plantar shear sensing transducer was developed, characterized, and tested in this study. Electro-optical components were chosen for the design because of the fast response time, low cost, small size, low power requirements, and adaptability to this application. The optoelectric circuit employed a 660 nm wavelength light source and photodiode solar cell. Signal amplification and sensitivity were adjusted to provide an output voltage proportional to light power. The sensor shell was designed to encapsulate the electro-optical sensing components while providing mechanical resistance to shear through a spring mechanism. A naval bronze was chosen for the shell due to its strength and nonreflective characteristics (alloy of copper and tin). Static and dynamic characteristics of the shear sensor were determined through a series of calibration tests. Mechanical crosstalk sensitivity ranged from 14.34 to 30.51 mV/N. This represented 1% full-scale/Newton sensitivity. Nonlinearity averaged 5.6% in the forward direction and 7.6% in the reverse direction. Overall sensor output hysteresis was 1.1 +/- 3.1% while the natural frequency of the sensor to an input shear transient was approximately 5 Hz. Temperature sensitivity was -7.0 mV/degree C or 3.5% full-scale/degree C. Testing of five adult subjects revealed peak anterior-posterior shear ranging from 6.7 kPa (posterior heel) to 51.4 kPa (great toe) and medial-lateral shear ranging from 5.4 kPa (great toe) to 43.5 kPa (first metatarsal head). Stress-time integral values ranged from 0.78 kPa-sec (posterior shear at the posterior heel) to 37.3 kPa-sec (medial shear at the posterior heel). Contact durations ranged from 0.28 sec (posterior shear at the posterior heel) to 1.25 sec (medial shear at the posterior heel). Further application of the sensor for plantar shear characterization in able-bodied subjects and those with pathology is suggested.

Investigation of spectral content from discrete plantar areas during adult gait: an expansion of rehabilitation technology

Evaluation of foot contact frequency components with the use of a standard force plate has been reported to be helpful in the clinical assessment of degenerative joint disease. Spectral analysis has also been used as a tool for the evaluation of prosthetic and orthotic designs. In this paper, we examine and employ a new method for determining spectral characteristics of discrete plantar foot surface areas. This method is used to characterize spectral frequency content of foot strike at discrete plantar locations in ten normal controls. Spectral data obtained from a standard force plate are also presented and compared to reports in the literature. Measurements at six discrete points under the foot were made with a custom-manufactured strain gage-based force dosimeter. In addition, measurements of ground reaction forces in the sagittal, coronal, and transverse planes were made using a high resonant frequency force plate during barefoot and shod walks for ten adult male control subjects. Spectral frequency components of all forces measured were determined through Fourier analysis. The hypothesis of the study was that discrete plantar frequencies would be essentially similar to those reported in earlier studies of foot contact with a ground reaction force plate. While Fourier transform of time domain force plate data revealed frequency contents that were contained primarily below 10 Hz, as has been previously reported, higher frequency components associated with impulsive loading at heel strike were also observed (75 Hz for barefoot walk and 60 Hz for shod). The anterior-posterior (AP) frequency spectrum of barefoot walking contained higher amplitude components than did shod walking, though both signals contained dominant frequencies of about 1 Hz. Medial-lateral (ML) frequency analyses were similar for both walking conditions with dominant components of about 4 Hz noted. Broader frequency spectrums were seen in the discrete force dosimeter data. Components were contained mostly below 12 Hz with some higher frequency content also noted. Discrete foot force dosimeter and force plate AP and ML spectral data during ambulation have not been previously reported.

"Guided" intramuscular fine wire electrode placement. A new technique

This report describes a new technique for placing intramuscular fine wire electrodes into muscles for kinesiologic electromyographic (EMG) studies. Currently, a pair of fine wire electrodes (one active, one reference) within a hypodermic needle is inserted into the selected muscle. The needle is then withdrawn, leaving the two fine wires positioned within the muscle. Electrical stimulation of the muscle through these fine wire electrodes confirms their correct placement. However, if positioning is incorrect, additional pairs of wires are inserted within needles until correct placement is achieved. Our "guided" method combines this "blind" technique with diagnostic needle EMG techniques. Using a conventional EMG machine and selective activation of the desired muscle, the electromyographer inserts the hypodermic needle while monitoring the muscle's electrical signal through the advancing fine wire electrodes. This signal is used to "guide" the needle into the proper muscle. Once correct positioning of the wires is confirmed by the EMG signal, the needle is removed. With this techniques additional needle insertions are avoided, electrical stimulation is seldom needed, and rarely studied muscles are accessed as easily as commonly studied ones. We have used this technique with pediatric and adult patients as well as in kinesiologic EMG research and have found it to be well tolerated and reliable.

A Holter-type microprocessor-based rehabilitation instrument for acquisition and storage of plantar pressure data in children with cerebral palsy

A multichannel, portable data acquisition system has been developed to measure discrete plantar pressures in the rehabilitation of children who have cerebral palsy and planovalgus foot deformity. The microprocessor-based system is designed to be lightweight (350 g with batteries) and portable (no umbilicus) in order to minimize encumbrances to gait patterns. It provides an improved method for obtaining accurate and reliable data during extended recording and rehabilitative periods that is not available from commercial systems. Twelve conductive polymer force (pressure) sensors are used to acquire pressure data, which are then stored in the system memory. Plantar pressures are sampled at a rate of 40 Hz from each of the 12 sensors for up to 2 h. The system consists of 16 analog amplifiers, a 12 b sampling analog-to-digital converter, an 8 b Dallas semiconductor microprocessor (DS5001FP-16, Dallas, TX), 4 MB of pseudo static RAM, and serial and parallel I/O interfaces. The interfaces are used to upload data into a PC for further processing, analysis, and display. During subject testing, sensors are located at predetermined anatomic areas under the calcaneus, medial and lateral midfoot, medial and lateral metatarsal heads, and hallux. Foot pressure data has been acquired from two pediatric subjects during multiple walking trials to illustrate system application in the normal and planovalgus foot. The system is considered to be appropriate for further clinical application and for characterization of event related alterations including rehabilitative, therapeutic, surgical, and nonsurgical treatment.

A system for the analysis of foot and ankle kinematics during gait

A five-camera Vicon (Oxford Metrics, Oxford, England) motion analysis system was used to acquire foot and ankle motion data. Static resolution and accuracy were computed as 0.86 +/- 0.13 mm and 98.9%, while dynamic resolution and accuracy were 0.1 +/- 0.89 and 99.4% (sagittal plane). Spectral analysis revealed high frequency noise and the need for a filter (6 Hz Butterworth low-pass) as used in similar clinical situations. A four-segment rigid body model of the foot and ankle was developed. The four rigid body foot model segments were 1) tibia and fibula, 2) calcaneus, talus, and navicular, 3) cuneiforms, cuboid, and metatarsals, and 4) hallux. The Euler method for describing relative foot and ankle segment orientation was utilized in order to maintain accuracy and ease of clinical application. Kinematic data from a single test subject are presented.

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.

Plantar pressures with total contact casting

Total contact casting has been used to aid in the healing of plantar neurotrophic ulcerations. The efficacy of total contact casts in promoting ulcer healing is presumably due to a reduction in the load over high pressure areas with pressure redistribution over the entire surface of the foot. The purpose of this study was to quantify the effectiveness of total contact casting in reducing plantar pressures. A portable microprocessor-based data-acquisition system was used for recording plantar pressures. Plantar pressures were collected from six nondisabled individuals with and without total contact casting at cast-walking cadence. In our study, there was a decrease in plantar loading under the metatarsal heads (first, fourth, fifth), the great toe, and the heel. The average decrease was 32% under the fifth metatarsal, 63% under the fourth metatarsal, 69% under the first metatarsal, 65% under the great toe, and 45% under the heel. Our study quantitatively showed that total contact casting does reduce vertical plantar pressures in high load areas.

Comparison of two fixation methods of oblique lesser metatarsal osteotomies: a biomechanical study

Two methods of internal fixation of oblique lesser metatarsal osteotomies were compared biomechanically using fresh-frozen human cadaver bones. Osteotomies were made obliquely through the metatarsal shafts and fixed with either crossed Kirschner wires or a single AO screw using the lag technique. The specimens were then fixed at their proximal end and loaded to failure using an axial torsion material testing system (MTS, Minneapolis, MN). Load displacement curves were obtained and the stiffness of the constructs were determined. Single-screw fixation was found to be significantly stiffer than the crossed wire configuration (P < .01). Single-screw fixation resulted in a stiffness of 211.2 +/- 111.7 N/cm (mean +/- SD), while stiffness of the crossed wire configuration averaged 56.9 +/- 25.1 N/cm.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.