In-shoe foot pressure measurement system utilising piezoelectric film transducers

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.

Design and test of a soft plantar force measurement system for gait detection

This work describes a plantar force measurement system. The MEMS pressure sensor, as the key sensing element, is designed, fabricated and embedded into a flexible silicon oil-filled bladder made of silicon rubber to constitute a single sensing unit. A conditioning circuit is designed for signal processing and data acquisition. The characteristics of the plantar force sensing unit are investigated by both static and dynamic tests. A comparison of characteristics between the proposed plantar force sensing unit and a commercial flexible force sensor is presented. A practical experiment of plantar force measurement has been carried out to validate the system. The results demonstrate that the proposed measurement system has a potential for success in the application of plantar force measurement during normal gait.

Assessment of spatio-temporal gait parameters from trunk accelerations during human walking

This paper studies the feasibility of an analysis of spatio-temporal gait parameters based upon accelerometry. To this purpose, acceleration patterns of the trunk and their relationships with spatio-temporal gait parameters were analysed in healthy subjects. Based on model predictions of the body's centre of mass trajectory during walking, algorithms were developed to determine spatio-temporal gait parameters from trunk acceleration data. In a first experiment, predicted gait parameters were compared with gait parameters determined from ground reaction forces measured by a treadmill. In a second experiment, spatio-temporal gait parameters were determined during overground walking. From the results of these experiments, it is concluded that, in healthy subjects, the duration of subsequent stride cycles and left/right steps, and estimations of step length and walking speed can be obtained from lower trunk accelerations. The possibility to identify subsequent stride cycles can be the basis for an analysis of other signals (e.g. kinematic or muscle activity) within the stride cycle.

Temporal gait analysis of hip osteoarthritic patients operated with cementless hip replacement

OBJECTIVE

This study attempts to identify temporal gait parameters, which characterize the pre- and postoperative course of hip monoarthritic patients who undergo cementless hip replacement.

BACKGROUND AND METHODS

Twenty-five female hip monoarthritic subjects (mean age 51, SD 5.0) were studied preoperatively; 20 out of them were studied at 1 and 8-10 years after the operation with a 22-m conductive walkway system using telemetry. A gender-matched control group was also studied (mean age 60, SD 2.0). The assessed parameters are the gait cycle duration, the single and double support, the single step duration and the gait speed.

RESULTS

The results indicate that improvement in patients' conditions following the operation occurs rapidly during the first postoperative year. Yet the hip has not reached optimal performance 1 year postoperatively; 8-10 years later it seems to have reached its optimal performance and remains in good condition. However, it still is below that of the controls.

CONCLUSIONS

Single support duration and speed are crucial in characterizing the functional restitution of patients after hip replacement.

RELEVANCE

An orthopaedic surgeon who attempts to quantify the postoperative course of hip monoarthritic patients after cementless hip replacement can focus at those temporal factors, which are typical of the functional restitution after the operation, without losing any valuable information given by other values.

Software for temporal gait data analysis

This study presents a computer program, developed to support a low-cost, portable telemetry system that has been designed to assess footfall timing. This software frees the user from data processing and allows concentration on data analysis. The new technique has been applied with accuracy and reliability to the analysis of the gait of orthopedic patients, athletes, mountaineers, etc. The subroutines developed for data acquisition, storage and analysis are explained in detail, and an example is presented.

A cheap telemetric system for analyzing gait

This study presents a technique for gait analysis, developed for the assessment of footfall timing and speed. The system in question consists of a transmitter, a receiver, a conductive walkway and a PC with the appropriate software. The technique was first tested for accuracy and repeatability with known signals, and was validated with a group of 20 healthy male adults (mean age = 34 years, S.D. = 5.5). The results thus obtained were similar to those reported in the literature for corresponding groups. Then, measurements on 10 children suffering from cerebral palsy (spastic hemiplegia) were performed. Gait analysis was carried out just before surgery and one year post-operatively. The results confirm the validity of the technique for measurements on orthopedic patients and its efficiency for functional evaluation of gait improvement after surgery.

A portable system for the measurement of the temporal parameters of gait

An easy-to-use, low cost, portable system is presented. It consists of a transmitter, four electrical sensors, a receiver and a PC with the appropriate software. The system can assess footfall timing, that is the single limb support, double limb support, single step duration values, and the gait cycle duration. This system has been tested for its accuracy with known signals. Then, measurements on a group of twenty (20) healthy adults were performed, with statistically insignificant (p>0.2) results to those reported in the literature. The above prove the system's validity for temporal gait analysis.

Reliability of measurements of pressures applied on the foot during walking by a computerized insole sensor system

OBJECTIVE

To evaluate the reliability of measurements of foot pressures while walking using the F-scan computerized system with various insole sensors.

DESIGN

Ten healthy subjects were studied. Each used four different pairs of insoles while walking for three 6-second epochs per insole. Peak pressures were recorded at the hindfoot, midfoot, and forefoot and analyzed. Each insole was made of pressure-sensitive 25 mm 2 cells, embedded in protective backing, and scanned electronically every 50 to 100 msec.

SETTING AND PARTICIPANTS

Conventional tile floor in a gait laboratory on 10 consecutive normal subjects.

RESULTS

The mean +/- standard deviation peak pressure recorded at the hindfoot was 11.1 +/- 2.0 psi; at the midfoot, 3.5 +/- 1.5 psi; and at the forefoot, 11.3 +/- 2.6 psi. The intrasubject mean differences were 0.2 psi at the hindfoot, 0.4 psi at the midfoot, and 0.3 psi at the forefoot. The data suggest that variability between different insoles is not significant.

CONCLUSION

The pressure data show these insoles to be sufficiently reliable for use in patients when knowledge of foot pressure distribution is important for the relief of pain, and for designing and assessing appropriate corrective measures to relieve excessive pressure on the foot and to prevent development of pressure ulcers.

Lower limb muscle dysfunction may contribute to foot ulceration in diabetic patients

OBJECTIVES

To investigate the relationship between in-shoe plantar foot pressure and the co-ordinated activity of five lower limb muscles of diabetic patients, who are known to have a higher risk of foot morbidity.

DESIGN

A portable six channel electromyographic system has been designed, developed and synchronised in real time with a 16 channel piezoelectric transducer in-shoe pressure measuring device, Gaitscan.

BACKGROUND

So far, no one has tried to establish a relationship between in-shoe foot pressure distribution and muscle activity of the lower limb in diabetes. The measurement of phasic muscle activity has been related to foot pressure and compared to a control group of normal volunteers.

METHODS

Twenty nine diabetic subjects and 22 healthy non-diabetic volunteers have been studied by recording electromyography of lower leg muscles and in-shoe foot pressure measurements simultaneously.

RESULTS

In diabetic subjects, the period of contact pressure was greater than in normal control subjects (P<0.003). The initial forefoot time to contact with the ground was shorter in diabetics when compared to controls, indicating a faster forefoot contact. Of the dorsiflexor muscles, the Anterior Tibialis, normally contracting eccentrically at heel strike, was subject to a measurable delay in the initiation of contraction, of mean difference of 180 ms (P<0.001), in diabetic subjects when compared to the normal controls.

CONCLUSIONS

The late firing of Tibialis Anterior means that its normal modulating role in lowering the foot to the ground after heel strike through eccentric contraction is disturbed. The result is that the foot reaches the foot flat stage in a less ordered manner, subjecting it to high plantar pressures.

RELEVANCE

The results obtained may assist in planning realignment procedures of the foot and help prevent development of ulcers on the sole of the foot in high risk diabetic subjects.

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.

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.