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Journal of Rehabilitation Researchand Development Vol . 24 No . 2Pages 9—12

Measurement pressure under leprotic feetusing barograph

K . MOTHIRAM PATIL*, D .SC., AND H . SRINIVASAN**, P .R .C.S.

Indian Institute of Technology, Madras 600 036, Indiaand Central Leprosy Teaching and Research Institute, Chengalpattu, India

Abstract—This paper describes the measurement of pres-sure distribution under normal and leprotic feet using abarograph. The barograph consists of a glass plate illu-minated at its edges by flourescent lights . The top surfaceof the glass plate is covered by a thin sheet of opaquewhite plastic upon which the subject stands . Greaterpressure levels cause more intimate contact between theplastic and the glass, which results in the breakdown oftotal internal reflections within the glass . When viewedfrom a 45 degree inclined mirror placed below the glassplate, the areas of contact of the foot can be seen withlight intensity related to the applied pressure . The re-sulting image recorded photographically is scanned forpressure intensity patterns using a microdensitometer.The pressure intensities are calibrated using known weightsover specified areas . The method establishes character-istics of pressure distribution under normal feet . It con-firms that scars resulting from healed ulcers in leprosysubjects are discrete sites of very high pressures in therange of 90 to 110 N/cm2 . This is two to three times thepressure levels under normal feet . Scar regions combinedwith deformity of the foot increase these pressures tostill higher levels and possibly cause ulcers . The quan-titative values of pressures determined in this study forleprosy subjects during standing are helpful in identifyingproblem areas on the soles of the feet.

*Professor, Biomedical Engineering Division, Department of AppliedMechanics, Indian Institute of Technology, Madras 600 036, India

**Formerly Senior Orthopaedic Surgeon and Deputy Director, Cen-tral Leprosy Teaching and Research Institute, Chengalpattu, India

INTRODUCTION

Leprosy is caused by a bacterium called Myco-bacterium laprae, commonly known as leprosy ba-cillus or Hansen's bacillus . According to the 1981census, 4 million people—about 6 out of every1,000—in India have leprosy . Of these, 25 percentsuffer from physical defor.nities . Leprosy bacilliattack the nerves, causing loss of sensation andmuscular paralysis, which leads to physical deform-ities if the patient is not given early treatment . Suchnerve damage is irreversible and there is no hopefor regeneration. Since the mycobacterium lapraeattack directly on neurons, many leprosy patientshave no sensation at the affected sites.

Excessively high stress on the leprotic foot forprolonged periods causes many problems . Experi-mentally, it was shown that high stresses for pro-longed periods cause mechanical damage to skinand soft tissue by cutting off the blood supply tothe tissue (3,4) . At sites where pressure is abnor-mally high such tissue damage will occur withoutthe patient's knowledge . To minimize further darn-age to the tissue, special footwear needs to bedesigned that will redistribute high pressures . Thequantitative knowledge of pressure distribution un-der the leprotic foot is helpful in identifying problemareas on the sole of the foot.

In this paper, pressure distribution under standingfeet is studied using a barographic technique whereinthe pressure intensities are converted into intensitiesof light.

9

0Journal of Rehabilitation Research and Development Vol. 24 No . 2 Spring 1987

MATERIALS AND METHODS

RESULTS AND DISCUSSION

Numerous methods have been proposed for meas-uring pressure distribution under the sole of the footwhile standing . These methods have ranged fromthe use of simple to extremely complex measurementdevices . Early attempts to obtain the load distri-bution under the foot were qualitative measurementsmade from impressions in plaster, mud, clay, orother suitably deformable substances . However,because the load measuring medium is deformable,such methods tend to measure the shape of the footrather than the detailed load distribution . In contrastto the early measurement techniques, which werelargely qualitative, recent methods have providedmore quantitative information about pressure dis-tribution . For the purposes of this study, a baro-graphic technique was used.

The barograph consisted of a thick glass plate(1 .8m x 0 .45m x 0 .0125m) and a plane mirrorplaced below the glass plate at an angle of 45 degreesin a wooden box (Figure 1) . The glass plate wasilluminated by fluorescent lights along its longitutinalthickness . The top surface was covered by a thinopaque white plastic sheet upon which the subjectstood. When viewed from the 45 degree inclinedmirror placed below the glass plate, the areas offoot contact could be seen with light intensity relatedto the applied pressure, due to the phenomena of"breakdown of total internal reflection ." The phys-

Figure 2a.

ical principle involved in the operation of the tech-

Footprint of a normal subject as seen on the barograph.

nique was illustrated at length in Betts, et al . (1).The resulting image recorded photographically wasscanned for pressure intensity patterns using amicrodensitometer . Pressure intensities were cali-brated using known weights over specified areas.

PLAIN GLASS PLATECOVERED WITH THINSHEET OF WHITE

EFORMASLE PLASTIC

ZMIRROR

0-0 TOES

Et-0 METATARSAL HEADS

Ii--e MID-FOOT

HEEL

5 4 3 2

1 2 3 4

Lateral

Medial

Medial

Lateral

LEFT FOOT

RIGHT FOOT

Figure 2a shows the footprint of a normal subjectduring standing . The image of the footprint as seenfrom the barograph gave the qualitative pressuredistribution, whereas quantitative pressure distri-bution was obtained by scanning the photographicnegative of the footprint using the microdensitom-eter . Figure 2a indicates the presence of a clearmedial arch . Light intensities appear to be evenlydistributed from the medial to lateral side and fromforefoot to hindfoot.

Figure 1.Schematic diagram of the barograph .

Figure 2b.Pressure distribution on the soles of normal feet .

11

PATIL AND SRINIVASAN, Barographic pressure measurement under leprotic feet

Figure 2b shows the quantitative distribution ofpressure on the sole of normal feet, which is dividedinto 16 zones consisting of five each for toes andmetatarsal heads and three each for midfoot, heelregions, respectively . The following observationswere made from the quantitative normal pressuredistributions:

1) The peak pressure in any part of the sole ofthe feet did not exceed 35N/cm' (350 kPa).

2) The peak pressure ratios of forefoot to hindfootas well as medial to lateral foot were found to benearly the same . This is in agreement with theresults of Betts, et al . (2).

3) Symmetrical pressure patternstween the left and right foot.

4) The ratio of peak pressure tounder the feet was equal to 14 .1.

Similar foot pressure distributionwere made on 16 normal subjects.

Figure 3a.Barographic image or footprint of leprosy subject

withflat feet .

clearly seen in the footprints of both feet by highintensity light spots at the corresponding locations.Figure 3b presents the quantitative pressure distri-bution for leprosy subject "a" . The pressure distri-bution showed high pressures of 110 to 130N/cm'(1100 to 1300 kPa) in the medial arches and healedulcer scar regions of the metatarsal heads and heels.The abnormally high pressures were two to threetimes those of normal pressures.

Figure 4a shows the footprint of a leprosy subjectwith posterior tibial nerve motor and sensory pa-ralysis of both feet . Scars were observed on thesecond and third metatarsal heads and heel of theleft foot and the first metatarsal head and heel ofthe right foot . Figure 4b presents quantitative pres-sure distribution at different locations of the feet.The pressure distributions showed high pressuresof 105N/cm' (1050 kPa ; two to three times normalpressure value) in the healed ulcer scar regions.

Similar studies made on other leprosy subjectsshowed nonsymmetric pressure distributions be-tween the left and right foot . The regions of scarsdue to healed ulcer showed high pressure zones;two to three times normal pressure zones . Footdeformity increased these pressures to a still higherlevel of 110 to 130N/cm' (1100—1300 kPa) and pos-sibly caused ulcers.

Figure 3b.Pressure distribution on the soles of leprosy subject "a ."

p 3

1~354

22

4 5Lateral

medial Medial

Lateral

LEFT FOOT

RIGHT FOOT

were seen be-

can pressure

measurementsThe ratios of

peak pressure to the mean pressure, with 95 percentconfidence interval, was in the range of 13 .8 to 19 .3,and no localized high pressure zones were observed.Peak pressure ratios of the forefoot to hindfoot werefound to be nearly equal to unity with a significancelevel of five percent.

The pressure distributions under the feet of rep-resentative leprosy subjects with deformity and scartissue are illustrated in Figures 3 and 4 . Figure 3ashows the footprints of a leprosy subject with flatfeet. The toes of the left foot are either absorbed oramputated and therefore are not seen in the foot-print. Clinical findings showed scars on the meta-tarsal heads and heels of both the feet . This was

2Journal of Rehabilitation Research and Development Vol . 24 No . 2 Spring 1987

CONCLUSIONS AND FUTURE PLANS

The barographic method of finding pres

- is-tribution on the sole of the foot drina : . ding.drngestablished characteristics of norm '

.e dis-tribution patterns . In leprosy subject

footabnormalities, the pressure

,tribution was notsymmetric between left a d .

ii foot ; instead, itgave rise to high pressure inei . The barographic

Figure 4a.Footprint of

'Meet with F .T . nerve motor andsensory pi i

h feet .

ToesMetatarsal heads

ti Mid foot

A Heel

RIGHT FOOT

F,saris distributioli

rtsn, if dolor and sm .

study confirmed that the scars resulting from healedulcers in leprosy subjects were discrete sites of veryhigh pressures of 90 to 110N/cm' (900–1100 kPa;two to three times normal pressure) . Foot deform-ities increased these pressures to a still higher levelof110 to 130 Nlem2 (1100 to 1300 kPa), and possiblycaused ulcers . The quantitative values of pressuresdetermined here for leprosy subjects were of greathelp in identifying problem areas on the sole of thefoot. The study will seek to identify peak pressureareas when the heel is lifted during walking.

Presently, the barograph helps the analysis of thebare foot on a flat surface . A future plan is tocomputerize analyses of barographic foot pressuresfor use in studying pressure patterns during walkingand in designing shapes of footwear insoles andinserts fitted under the insoles for leprosy patients.

Footwear design will include the following pro-cedures. Barographic pressure patterns under a thininsole material of 2 mm thickness with a flat bottomsurface will be recorded . The shape of the insolematerial will be varied, and correlations betweeninsole material shape and pressure patterns underthe insole of both normal and leprosy subjects willbe determined . If a positive correlation is achieved,we may be able to generate a footwear insole shapefor leprosy subjects that redistributes and minimizesareas of high pressure, thereby preventing furtherulcer formation or other damage to the soft tissue.

The effects on the pressure map of differentpreshaped inserts fitted under the insole of footwearworn by leprosy patients with foot deft ,-mities alsowill be studied . The final goal is to ,h ie r n insoleon a computer monitor using data ii o the originalpressure map and then transfer this sh o into insolefootwear material . It is hoped that the barographicpressure pattern study will assist in designing indi-vidualized footwear for leprotic persons.

REFERENCES

BETTS RP, DUCK ,T, AND AUSTIN IG. Critical lightreflection at r pl .

t :,

i --face and its application tofoot pressure

. J Wed Eng Tech, 4(3), 136-

, 1980(a).2. R P, FRANKS t51, DUCKWORTH T . AND BURKE T.

id dynamic foot pressure me

Nni , in clinical

orthop dies . Tlrled BM Eng Comput, 18, 67 -684, I980(b).3. T1 . .,

'F . An experimental study of some pressureal tissue with reference to the bed sore problem.

J cif!' act, 66, : 7-358, 1953.4. fviu gNi i FR Tr'

ii — Mg load to flesh . Part 1 : Concept.Bull Prosthet Rr

1 -' c 38-44, 1971.

Imp

1

I

i

i

5 r 3 2Lateral

Medial

LEFT FOOT