Method for in-shoe shear stress measurement

Commercially available pressure sensors for sport and health applications: A comparative review

Pressure measurement systems have numerous applications in healthcare and sport. The purpose of this review is to: (a) describe the brief history of the development of pressure sensors for clinical and sport applications, (b) discuss the design requirements for pressure measurement systems for different applications, (c) critique the suitability, reliability, and validity of commercial pressure measurement systems, and (d) suggest future directions for the development of pressure measurements systems in this area. Commercial pressure measurement systems generally use capacitive or resistive sensors, and typically capacitive sensors have been reported to be more valid and reliable than resistive sensors for prolonged use. It is important to acknowledge, however, that the selection of sensors is contingent upon the specific application requirements. Recent improvements in sensor and wireless technology and computational power have resulted in systems that have higher sensor density and sampling frequency with improved usability - thinner, lighter platforms, some of which are wireless, and reduced the obtrusiveness of in-shoe systems due to wireless data transmission and smaller data-logger and control units. Future developments of pressure sensors should focus on the design of systems that can measure or accurately predict shear stresses in conjunction with pressure, as it is thought the combination of both contributes to the development of pressure ulcers and diabetic plantar ulcers. The focus for the development of in-shoe pressure measurement systems is to minimise any potential interference to the patient or athlete, and to reduce power consumption of the wireless systems to improve the battery life, so these systems can be used to monitor daily activity. A potential solution to reduce the obtrusiveness of in-shoe systems include thin flexible pressure sensors which can be incorporated into socks. Although some experimental systems are available further work is needed to improve their validity and reliability.

Predicting vertical and shear ground reaction forces during walking and jogging using wearable plantar pressure insoles

BACKGROUND

The development of plantar pressure insoles has made them a potential replacement for force plates. These wearable devices can measure multiple steps and might be used outside of the lab environment for rehabilitation and evaluation of sport performance. However, they can only measure the vertical force which does not completely represent the vertical ground reaction force. In addition, they are not able to measure shear forces which play an import role in the dynamic performance of individuals. Indirect approaches might be implemented to improve the accuracy of the force estimated by plantar pressure systems.

RESEARCH QUESTION

The aim of this study was to predict the vertical and shear components of ground reaction force from plantar pressure data using recurrent neural networks.

METHODS

Ground reaction force and plantar pressure data were collected from 16 healthy individuals during 10 trials of walking and five trials of jogging using Bertec force plates at 1000 Hz and FScan plantar pressure insoles at 100 Hz. A long short-term memory neural network was built to consider the time dependency of pressure and force data in predictions. The data were split into three subsets of train, to train the model, evaluate, to optimize the model hyperparameters, and test sets, to assess the accuracy of the model predictions.

RESULTS

The results of this study showed that our long short-term memory model could accurately predict the shear and vertical force components during walking and jogging. The predictions were more accurate during walking compared to jogging. In addition, the predictions of mediolateral force had higher error and lower correlation compared to vertical and anteroposterior components.

SIGNIFICANCE

The long short-term memory model developed in this study may be an acceptable option for accurate estimation of ground reaction force during outdoor activities which can have significant impacts in rehabilitation, sport performance, and gaming.

Diabetic Foot Considerations Related to Plantar Pressures and Shear

Diabetic foot ulcers are a complex, multifaceted, and widespread complication of diabetes mellitus. Although there are a multitude of risk factors contributing to diabetic foot ulcer development, pressure and (more recently) shear stresses are two biomechanical metrics that are gaining popularity for monitoring risk factors predisposing skin breakdown. Other areas of diabetic foot ulcers under research include plantar temperature measuring, as well as monitoring wear-time compliance and machine learning/AI algorithms. Charcot arthropathy is another diabetes complication that has a relationship with diabetic foot ulcer development, which should be monitored for development alongside ulcer development. The ability to monitor and prevent diabetic foot ulcer development and Charcot neuroarthropathy will lead to increased patient outcomes and patient quality of life.

A Review of Wearable Sensor Systems to Monitor Plantar Loading in the Assessment of Diabetic Foot Ulcers

Diabetes is highly prevalent throughout the world and imposes a high economic cost on countries at all income levels. Foot ulceration is one devastating consequence of diabetes, which can lead to amputation and mortality. Clinical assessment of diabetic foot ulcer (DFU) is currently subjective and limited, impeding effective diagnosis, treatment and prevention. Studies have shown that pressure and shear stress at the plantar surface of the foot plays an important role in the development of DFUs. Quantification of these could provide an improved means of assessment of the risk of developing DFUs. However, commercially-available sensing technology can only measure plantar pressures, neglecting shear stresses and thus limiting their clinical utility. Research into new sensor systems which can measure both plantar pressure and shear stresses are thus critical. Our aim in this paper is to provide the reader with an overview of recent advances in plantar pressure and stress sensing and offer insights into future needs in this critical area of healthcare. Firstly, we use current clinical understanding as the basis to define requirements for wearable sensor systems capable of assessing DFU. Secondly, we review the fundamental sensing technologies employed in this field and investigate the capabilities of the resultant wearable systems, including both commercial and research-grade equipment. Finally, we discuss research trends, ongoing challenges and future opportunities for improved sensing technologies to monitor plantar loading in the diabetic foot.

Measuring Plantar Tissue Stress in People With Diabetic Peripheral Neuropathy: A Critical Concept in Diabetic Foot Management

Excessive stress on plantar tissue over time is one of the leading causes of diabetic foot ulcers among people with diabetic peripheral neuropathy. Plantar tissue stress (PTS) is a concept that attempts to integrate several well-known mechanical factors into one measure, including plantar pressure, shear stress, daily weight-bearing activity, and time spent in prescribed offloading interventions (adherence). Despite international diabetic foot guidelines recommending the measure of each of these individual mechanical factors in people with neuropathy, only recently has technology enabled their combined measurement to determine PTS. In this article we review the concept of PTS, the mechanical factors involved, and the findings of pivotal articles reporting measures of PTS in people with neuropathy. We also discuss key existing gaps in this field, including the lack of standards to measure and report PTS, a lack of practical solutions to measure shear stress, and the lack of PTS thresholds that may indicate benefit or detriment to people with neuropathy. To address some of these gaps, we propose recommended clinical and research standards for measuring and reporting PTS in people with neuropathy. Last, we forecast future clinical, research, and technological advancements that may use PTS to highlight the importance of this critical concept in the prevention and management of diabetic foot ulcers.

Plantar shear stress measurements - A review

BACKGROUND

Mechanical stress at the plantar surface has two components, pressure acting normal to the surface and shear stress acting tangential to the surface. Typically only pressure is measured and reported. However, plantar shear stress also plays a major role, especially in diabetic ulceration.

METHODS

During the last few decades, a variety of methods have been developed for the measurement of plantar shear stress. This paper reviews the technologies used in plantar shear stress measurements.

FINDINGS

Several technologies have been used, e.g. magneto-resistors, strain gauges, optical methods, piezoelectric materials and capacitive sensors. Examples of plantar shear stress values measured with the developed devices are also collected here and the relationship between sensor characteristics and the measured plantar shear stress distribution is discussed.

INTERPRETATION

Even with the limitations of current plantar shear stress measurement technologies, they can provide useful information on the plantar stress distribution.

Biomechanical Properties of the Foot Sole in Diabetic Mellitus Patients

This aricle evaluates and quantifies the biomechanical properties of the foot sole like – loss of protective sensation, hardness of the foot sole and pressure distribution parameter called Power ratio (PR) and its alterations, which have a direct effect on ulcer formation. A new parameter PRS Index is developed to understand the interplay between these parameters and its role in ulcer formation. All diabetic subjects attending the Diabetic foot clinic from Dec2003 to June 2007 undergo a standard foot examination.A total of 652 diabetic patients including 57 ulcer patients are taken for our study. The biomechanical properties include loss of protective sensation (LOPS) which is measured by 10 gm Semmes Weinstein Monofilament (SWMF). Hardness of the foot sole or absence of suppleness is tested using the Durometer (ASTM-D 2240 standards). Plantar pressure measurement is done using the PedoPowerGraph(p) which measures pressure distribution parameter PR. Foot wear properties like hardness of the insole affecting the formation of plantar ulcers was also measured. The above mentioned important parameters can be measured objectively and calculate PRS index value for diabetic with history of previous ulcer patients. We found a single entity of either the PR or shore independently cannot predict the risk for ulcer formation.In this study we found newPRS index value for diabetic with history of previous ulcer patients show significant correlation (i.e. p<0.05 level) between footwear shore and PRS index for history of previous ulcer patients. No significant correlation was shown for diabetic without history of previous ulcer patients and this may be due to diabetic patients are wearing footwear randomly with different degree Shore. From the case studies we found that the PRS index values and other biomechanical parameter of the foot sole can be reversed if the patients wear proper MCR footwear with 20 degree Shore. Use of appropriate footwear has shown that these easily measurable parameters and thus prevent ulcer formation as mentioned in the earlier studies. Several methods are used previously for predicting ulceration in DM patients. But in this study the new index PRS was studied and its role in predicting ulceration. Use of appropriate footwear will reverse the hypertrophic response; this can be quantified by the PRS index. We have found that there is decrease in PRS index by proper off loading the pressure using 20-degree shore MCR footwear.

The use of fiber Bragg grating sensors in biomechanics and rehabilitation applications: the state-of-the-art and ongoing research topics

In recent years, fiber Bragg gratings (FBGs) are becoming increasingly attractive for sensing applications in biomechanics and rehabilitation engineering due to their advantageous properties like small size, light weight, biocompatibility, chemical inertness, multiplexing capability and immunity to electromagnetic interference (EMI). They also offer a high-performance alternative to conventional technologies, either for measuring a variety of physical parameters or for performing high-sensitivity biochemical analysis. FBG-based sensors demonstrated their feasibility for specific sensing applications in aeronautic, automotive, civil engineering structure monitoring and undersea oil exploration; however, their use in the field of biomechanics and rehabilitation applications is very recent and its practicality for full-scale implementation has not yet been fully established. They could be used for detecting strain in bones, pressure mapping in orthopaedic joints, stresses in intervertebral discs, chest wall deformation, pressure distribution in Human Machine Interfaces (HMIs), forces induced by tendons and ligaments, angles between body segments during gait, and many others in dental biomechanics. This article aims to provide a comprehensive overview of all the possible applications of FBG sensing technology in biomechanics and rehabilitation and the status of ongoing researches up-to-date all over the world, demonstrating the FBG advances over other existing technologies.

Effect of heel height on in-shoe localized triaxial stresses

Abnormal and excessive plantar pressure and shear are potential risk factors for high-heeled related foot problems, such as forefoot pain, hallux valgus deformity and calluses. Plantar shear stresses could be of particular importance with an inclined supporting surface of high-heeled shoe. This study aimed to investigate the contact pressures and shear stresses simultaneously between plantar foot and high-heeled shoe over five major weightbearing regions: hallux, heel, first, second and fourth metatarsal heads, using in-shoe triaxial force transducers. During both standing and walking, peak pressure and shear stress shifted from the lateral to the medial forefoot as the heel height increased from 30 to 70mm. Heel height elevation had a greater influence on peak shear than peak pressure. The increase in peak shear was up to 119% during walking, which was about five times that of peak pressure. With increasing heel height, peak posterolateral shear over the hallux at midstance increased, whereas peak pressure at push-off decreased. The increased posterolateral shear could be a contributing factor to hallux deformity. It was found that there were differences in the location and time of occurrence between in-shoe peak pressure and peak shear. In addition, there were significant differences in time of occurrence for the double-peak loading pattern between the resultant horizontal ground reaction force peaks and in-shoe localized peak shears. The abnormal and drastic increase of in-shoe shear stresses might be a critical risk factor for shoe-related foot disorders. In-shoe triaxial stresses should therefore be considered to help in designing proper footwear.

Ambulatory assessment of 3D ground reaction force using plantar pressure distribution

This study aimed to use the plantar pressure insole for estimating the three-dimensional ground reaction force (GRF) as well as the frictional torque (T(F)) during walking. Eleven subjects, six healthy and five patients with ankle disease participated in the study while wearing pressure insoles during several walking trials on a force-plate. The plantar pressure distribution was analyzed and 10 principal components of 24 regional pressure values with the stance time percentage (STP) were considered for GRF and T(F) estimation. Both linear and non-linear approximators were used for estimating the GRF and T(F) based on two learning strategies using intra-subject and inter-subjects data. The RMS error and the correlation coefficient between the approximators and the actual patterns obtained from force-plate were calculated. Our results showed better performance for non-linear approximation especially when the STP was considered as input. The least errors were observed for vertical force (4%) and anterior-posterior force (7.3%), while the medial-lateral force (11.3%) and frictional torque (14.7%) had higher errors. The result obtained for the patients showed higher error; nevertheless, when the data of the same patient were used for learning, the results were improved and in general slight differences with healthy subjects were observed. In conclusion, this study showed that ambulatory pressure insole with data normalization, an optimal choice of inputs and a well-trained nonlinear mapping function can estimate efficiently the three-dimensional ground reaction force and frictional torque in consecutive gait cycle without requiring a force-plate.

Local shear stress transduction

This is a comprehensive review of local direct measurement shear stress transducers. Transducers are first classified by their movement, measuring mode, and mechanism. These categories are then subclassified into active or passive movement, static or dynamic measuring mode, and rotational or translational mechanisms. Over 80 transducers are reviewed and tabulated. Finally, sources of transducer error are analyzed. Primary sources of error are transducer and housing misalignment, material ingress around the active face, active face roughness, and the effects of temperature gradients when making measurements on surfaces where temperature gradients develop.

Tri-axial plantar pressure sensor: design, calibration and characterization

A novel tri-axial plantar pressure sensor has been developed. This sensor simultaneously measures vertical plantar pressure and anterior-posterior and medial-lateral shear plantar pressures utilizing a central post, four parallel plates, and a commercial miniature pressure transducer. As a subject walks over the sensor, the central post is deflected and the shear pressures are measured utilizing capacitive sensing technology. The miniature pressure transducer (MPT) is simultaneously loaded to measure the vertical pressure. Each individual tri-axial plantar pressure sensor has the capability of measuring shear forces ranging from 0 to 15 N and vertical pressures ranging from 0 to 28 MPa. The shear component of the tri-axial pressure sensor has a sensitivity of 1.3 mV/g, a non-linearity of 8.3 %, and hysteresis of 7.3 %. The commercial vertical MPT has a sensitivity of 220 nv/V/psi, a non-linearity of 0.094%, and a hysteresis of 0.567%. An array of individual tri-axial plantar pressure sensors in the form of a platform will be developed to measure plantar pressure in patients. This pressure platform is placed on the surface of a walkway and is suitable for barefoot walking trials.

Effect of sock on biomechanical responses of foot during walking

BACKGROUND

Except the plantar pressure and gross joint motion, we know little about the mechanical state of a foot during walking. This study aimed at investigating the effect of wearing socks with different frictional properties on plantar shear, which is a possible mechanical risk factor of foot lesion development.

METHOD

A 3-D finite element model for simulating the foot-sock-insole contact was developed to investigate the biomechanical effects of wearing socks with different combinations of frictional properties on the plantar foot contact. The dynamic plantar pressure and shear stress during the stance phases of gait were studied through finite element computations. Three cases were simulated, a barefoot with a high frictional coefficient against the insole (0.54) and two socks, one with a high frictional coefficient against the skin (0.54) and a low frictional coefficient against the insole (0.04) and another with an opposite frictional properties assignment.

FINDINGS

Wearing sock of low friction against the insole to allow more relative sliding between the plantar foot and footwear was found to reduce the shear force significantly: at the rearfoot from 3.1 to 0.88 N, and at the forefoot from 10.61 to 1.61 N. The shear force can be further reduced to 0.43 N at the rearfoot, and 1.18 N at the forefoot, when wearing the sock with low friction against the foot skin and high friction set against the insole.

INTERPRETATION

Wearing sock with low friction against the foot skin was found to be more effective in reducing plantar shear force on the skin than the sock with low friction against the insole. The risk of barefoot walking in developing plantar shear related blisters and ulcers might be reduced by socks wearing especially those with low friction against the foot skin.

Simultaneous shear and pressure sensor array for assessing pressure and shear at foot/ground interface

Foot ulceration is a diabetic complication estimated to result in over $1 billion worth of medical expenses per year in the United States alone. This multifaceted problem involves the response of plantar soft tissue to both external forces applied to the epidermis and internal changes such as vascular supply and neuropathy. Increasing evidence indicates that a combination of elevated external forces (pressure and shear) and altered tissue properties is key to the etiology of foot ulcers. The overall goal of this research is to develop a platform-type hardware system that will allow a clinician to measure three-dimensional stress tensors (i.e. pressure and shear patterns) on the plantar surface and identify areas of concern. Experimental results have demonstrated that an optical approach can provide clear indication of both shear and pressure from 50 to 400 kPa with a frequency response of 100 Hz, a stress measurement accuracy of 100 Pa and a spatial resolution of 8.0mm. Initial evaluation of the system shows strong correlation between (i) applied shear and normal stress loads and (ii) the optical phase retardance computed for each stress axis of the polymer-based stress-sensing elements. These special sensing elements are designed to minimize the need for repeated calibration procedures-an issue that has plagued other attempts to develop multisensor shear and pressure systems.

Effects of total contact insoles on the plantar stress redistribution: a finite element analysis

OBJECTIVE

To investigate the effects of total contact insoles on the plantar stress redistribution using three-dimensional finite element analysis.

DESIGN

The efficacies of stress reduction and redistribution of two total contact insoles with different material combinations were compared with those of a regular flat insole used as a baseline condition.

BACKGROUND

Many specially designed total contact insoles are currently used to reduce the high plantar pressure in diabetic patients. However, the design of total contact insoles is mostly empirical and little scientific evidence is available to provide a guideline for persons who prescribe such insoles.

METHODS

To use three-dimensional finite element models of the foot together with insoles to investigate the effects of total contact insoles on the foot plantar pressure redistributions. Nonlinear foam material properties for the different insole materials and the contact behavior in the foot-insole interface were considered in the finite element analysis.

RESULTS

Results showed that the peak and the average normal stresses were reduced in most of the plantar regions except the midfoot and the hallux region when total contact insoles were worn compared with that of the flat insole condition. The reduction ratios of the peak normal stress ranged from 19.8% to 56.8%.

CONCLUSIONS

Finite element analysis results showed that the two sets of total contact insoles used in the current study can both reduce high pressures at regions such as heel and metatarsal heads and can redistribute the pressure to the midfoot region when compared with the flat insole condition.

RELEVANCE

It is possible to simulate foot deformities, change in material properties, different ambulatory loading conditions, and different orthotic conditions by altering the finite element model in a relatively easy manner and these may be of interests to the medical professionals who treat foot-related problems.

Simultaneous measurement of plantar pressure and shear forces in diabetic individuals

Plantar foot ulceration is a diabetic complication whose underlying causative factors are still not fully understood. The goal of the current work was to simultaneously record plantar pressure and shear and examine the interrelationship of these forces; specifically, if peak shear and pressure occurred at the same site/time and whether adjacent shear forces had a greater tendency to be directed towards or away from each other. A custom built 16 transducer array was used to record forefoot shear and pressure during gait initiation in a cohort of 12 neuropathic diabetic individuals. The individuals were barefoot and the transducers were covered with a 5 mm thick layer of Minorplast. The greatest pressure occurred in the medial metatarsal heads (189 kPa) and the greatest shear in the lateral metatarsal heads (33 kPa). The interaction of the shear forces revealed that the plantar tissue was stretched to a greater magnitude than it was bunched (24 kPa vs 12 kPa, averaged over all regions). Normal distributions were determined for stretching and bunching in both the medial-lateral and anterior-posterior directions. When shear and pressure were considered in combination, half of the neuropathic individuals had peak shear and pressure occurring at the same site. These peak stresses did not occur at the same time (average difference of 0.186 s). The results of this study help to further characterize tissue stresses experienced on the plantar surface of the foot during gait initiation in neuropathic diabetic individuals.

Surgical rehabilitation of the planovalgus foot in cerebral palsy

The objectives of this study were to quantitatively determine the effects of subtalar arthrodesis on the planovalgus foot using three-dimensional (3-D) gait analysis and plantar pressure measurements. Twelve children and adolescents with planovalgus foot deformity secondary to spastic cerebral palsy participated in this outcome study. The pediatric population were evaluated preoperatively and following subtalar fusion. Seventeen feet were operated for the correction of the planovalgus foot deformity. A Holter-type microprocessor-based portable in-shoe data acquisition system was used in this study to collect the multistep dynamic plantar pressure history, while a five-camera Vicon-based gait analysis system was used to track the lower extremity joint kinematics. The results obtained from the plantar pressure measurement showed significant increases in mean peak vertical plantar pressures postoperatively at the lateral midfoot and lateral metatarsal heads. Mean contact durations and mean pressure-time integrals were also significantly increased at these plantar locations following foot surgery. This redistribution in pressure metrics suggests the formation of new lateral plantar weight bearing areas. The 3-D gait analysis system, using standardized lower extremity measurements, was unable to reveal any significant changes in joint kinematics, particularly at the foot and ankle where the surgery was performed. This suggests the need for a more refined system to track the complex motion of the pediatric foot and ankle during gait.

A study of in-shoe plantar shear in patients with diabetic neuropathy

OBJECTIVE

To quantify in-shoe plantar shear in diabetic neuropathic feet.

DESIGN

Plantar shear stresses are measured in a group of six patients with a history of diabetic neuropathic ulceration.

BACKGROUND

Although elevated pressure between foot and shoe frequently found in diabetic neuropathic patients has been linked to a raised incidence of plantar ulceration, the shear component of stress at this interface is as yet unquantified. It is suggested that its effects may be equally damaging.

METHODS

Measurements of shear were made locally beneath the medial four metatarsal heads and heel during unpaced gait in orthopaedic footwear, using a bi-axial magneto-resistive shear transducer. Similar methodology was previously employed on a group of asymptomatic adults, thereby allowing comparisons to be made.

RESULTS

Overall the maximum shear stress for this patient group (73 kPa) was not significantly different to that in the asymptomatic group (87 kPa). However the patient group exhibited lower magnitudes of shear stress under the third/fourth metatarsal heads (average 51/39 vs. 86.5/71 kPa, respectively) and higher magnitudes under the first/second heads (73/64 vs. 35/31 kPa, respectively), indicating a medial shift. Step-to-step variability of maximum shear measured under the third metatarsal head showed an increase in the transverse component (coefficient of reliability 67% vs. 98%).

CONCLUSIONS

Although the overall patterns of shear are broadly similar to the asymptomatic group, these pilot trials indicate a medial shift in shear loading under the forefoot coupled to increased step-to-step variability in the diabetic group. RelevanceMechanical stress at the plantar interface between foot and shoe is of particular clinical relevance to the formation and management of ulcers in diabetic neuropathy. Whereas the pressure component of stress is widely studied, the shear component is poorly described although it may be of equal importance.

A study of in-shoe plantar shear in normals

OBJECTIVE

To quantify features of in-shoe plantar shear in asymptomatic adult gait.

DESIGN

In order to standardize footwear conditions and facilitate later comparison to patient groups, measurement is made in a group of adults walking freely in stock orthopaedic footwear.

BACKGROUND

Better data on plantar shear is required to complement well-documented pressure data for an overall picture of plantar stress.

METHODS

Measurements were made locally beneath the medial four metatarsal heads and heel using biaxial transducers mounted flush into an inlay. Pressure distribution was also measured.

RESULTS

The shear data revealed common features in the shear pattern occurring at defined phases of gait, with good inter-step reliability. For the five sites of interest, these values ranged from 24 kPa to 70.4 kPa, and 31 kPa to 86.5 kPa for individuals wearing nylon hose or hose-free respectively. Maximum shear occurred more laterally than maximum pressure.

CONCLUSIONS

Features of plantar shear were not always as expected; for example the forward thrust at push-off was not reflected in the anteroposterior shear stress. Because of the inter-subject variability, study of a larger group is indicated.

RELEVANCE

Mechanical stress at the plantar interface between foot and shoe is of particular clinical relevance to the formation and management of ulcers in diabetic neuropathy. It is also of relevance to shoe and orthotic design for various foot pathologies. This study provides reliable data on the shear component of plantar stress for which, unlike the well-documented pressure component, there is only sparse data so far available.

Use of computerized insole sensor system to evaluate the efficacy of a modified ankle-foot orthosis for redistributing heel pressures

OBJECTIVE

Evaluation of orthosis purported to decrease pressure on the heel while walking.

DESIGN

The Multipodus System is an orthotic device, designed for this purpose, that can be worn with flat or rocker bottom boot. Ten subjects underwent four trials: first, an initial walk wearing their usual shoes, then using the orthosis on the left, with a flat bottom boot, then with a rocker bottom boot, and a final walk. Pressures exerted on the plantar surface of the hindfoot, midfoot, and forefoot were measured electronically and analyzed.

SETTING AND PARTICIPANTS

Ten consecutive normal subjects were tested on a conventional tile floor in a gait laboratory.

RESULTS

Peak pressures in the initial walk averaged: heel, 9.6 +/- 2.3psi; midfoot, 2.6 +/- 1.7psi; and forefoot, 10.3 +/- 2.6psi. Pressures on the foot were redistributed significantly when the orthosis was used. Heel pressure was reduced significantly compared to the ordinary shoes using both the flat bottom boot (5.0 +/- 1.2psi, a decrease of 48% [p = .0001]) and the rocker bottom boot (4.5 +/- 1.5psi, a decrease of 53% [p = .0001]). Pressure was increased at the midfoot with both the flat bottom boot (6.6 +/- 3.2psi, an increase of 61% [p = .0001]) and the rocker bottom boot (6.8 +/- 2.9psi, an increase of 62% [p = .0001]). Pressures at the forefoot decreased 19% (8.3psi) with the flat bottom boot and 32% (7.0psi; p = .0003) with the rocker bottom boot.

CONCLUSIONS

Redistribution of pressure on the foot with orthosis is characterized by reduction at the hindfoot and forefoot and increase at the midfoot with both the flat and rocker bottom boots, thereby promoting healing of calcaneal and forefoot ulcers. The integrity of the midfoot, however, must not be compromised.

Properties of the flexible pressure sensor under laboratory conditions simulating the internal environment of the total surface bearing socket

The purpose of this study was to investigate the properties of the flexible pressure sensor under laboratory conditions simulating the internal environment of the total surface bearing (TSB) socket to determine optimal conditions for measuring normal stresses on the stump. The equipment used in the study was the Pressure Distribution Sensor System for Sockets. In a climatic chamber maintained at 37 degrees C and 70% humidity the sensor sheet was mounted on a measuring apparatus loaded with three 10 kg weights, and output from the sensor was recorded. Because of sensor creep, a sample 60 seconds after loading was adopted as the measured output. Output was greater when weight was decreased than when weight was increased because of hysteresis (paired t-test, p<0.05). The sensor had temperature sensitivity but differences in output were not statistically significant (paired t-test, 0.10>p>0.05). There were no significant differences in output among five sensor sheets or among five sections of four sensor sheets (two-way ANOVA, p>0.05), but repeated loading on the same section of the sensor sheet increased output (two-way ANOVA, p<0.05). Reproducibility and sensitivity distribution of the sensor are considered satisfactory under laboratory conditions, but measurements of rapid and repetitive movements may not be accurate and comparing subtle changes in output from a single sensor is not suitable. The reliability of the sensor in a clinical setting for measuring normal stresses on the stump with the TSB socket should be examined.

Shoe-surface interaction and the reduction of injury in rugby union

While it is quite clear that footwear can provide protection against lower limb injury in running and some court sports, the literature related to footwear design and injury prevention in most sports played on natural turf is limited. Nowhere is this more apparent than in the design of footwear for rugby union and rugby league. Therefore, in this article, information from other sporting codes will be applied to the design and performance characteristics of footwear and surfaces in an attempt to understand the causes of equipment-related injuries in rugby. A complete understanding of the complex interactions between the leg, foot, footwear and the surface has not yet been achieved and as a consequence, precise footwear design criteria to minimise injury, while not compromising the performance aspects of shoe design, have yet to be established. The variable surface conditions experienced by players makes it difficult to provide recommendations as to the ideal footwear for all (or any) conditions. Equally, the ground reaction loads experienced by each player (and playing position) vary sufficiently to make generalisations difficult. Also the foot-fall pattern during weight-bearing is highly individualised and further prohibits making general recommendations about selecting footwear for rugby.

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.

In-shoe biaxial shear force measurement: the Kent shear system

The Kent shear system is introduced and preliminary clinical results are presented. A technique utilising copolymer piezoelectric film has allowed the manufacture of biaxial in-shoe transducers capable of simultaneously measuring two orthogonal shear forces. Bipedal measurements are carried out inside everyday footwear over multiple footsteps.

The application of engineering and technology in the management of diabetes

Diabetes mellitus is a relatively common disorder in which many of the body's systems are affected, resulting in morbidity and mortality. Early diagnosis and good blood glucose control can delay or prevent the onset of these complications. This review illustrates how engineering and technology can help to achieve these goals.

Transducers for foot pressure measurement: survey of recent developments

Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation, performance and limitations. Examples of capacitive, piezo-electric, optical, conductive and resistive types of transducer are presented. Where available, the current clinical status is specified.

Some aspects of modern orthotics

Orthotics is changing more rapidly than ever before, largely resulting from improved understanding of the human requirements and the current state of technological abilities. Walking is always seen as a basic requirement for normal activity and as such it is in this area that most research and development effort is expended. This paper outlines some of the current developments in this interesting topic and includes seating and posture as these are often viewed as precursors to successful standing and then, possibly, gait.

The effect of shear forces externally applied to skin surface on underlying tissues

The effects of shear forces externally applied to the skin surface on the underlying tissues have been investigated. An analysis of the internal stresses and strains was conducted using a simplified model incorporating elasticity theory. Skin blood flow was measured using laser Doppler flowmetry while variable shear forces over a range of 0-250 g were applied to the skin surface. The theoretical model predicts that the application of surface shear forces alters the internal stress distribution and makes the shear and compressive components of stresses increase ahead of the surface force application point. The force resulting from concomitant application of shear and normal force determines the internal maximum stress and strain. Theoretically, the shear force should have the same effects on the underlying tissues as normal force. The experimental investigations revealed that the skin blood flow decreased roughly linearly with the increase of shear forces. When a shear force equal to the normal force was applied, the flux decreased by 45%, nearly equal to the increasing magnitude (41%) of resultant of normal and shear forces.

A biomechanical analysis of the plantar surface of soccer shoes

The incidence of severe injuries for soccer players may lead to long-term inactivity or, at worst, retirement from the game. Many of these injuries, particularly those involving the lower leg, can be attributed to adverse physical conditions at the interface between the soccer shoe and the playing support surface. This study investigated the biomechanical characteristics at this interface for a range of proprietary soccer shoes. An experimental system was designed and developed which, via a weighted pendulum arm making contact with a vertical column, provided controlled rotation of the forefoot of the soccer shoe on samples of playing surfaces. The overall rotation was found to depend on several physical and material factors. For example, the size 7 soccer shoes produced a statistically significant increase in axial rotation for the same impact energy compared to the larger sized shoes under test. In addition, flat soled shoes, designed for synthetic playing surfaces, produced consistently smaller rotations than shoes with either moulded or screw-in studs, although this finding depended on the moisture content of the playing surface. The pressure distribution within several soccer shoes was also measured using the F-Scan Gait Analysis System, for a subject walking across a grass surface. Results indicated differences in pressure distribution over the first metatarsal area of the foot, in existing shoe designs.