Annals of the Rheumatic Diseases, 1981, 40, 83-86

Stereophotogrammetry and relief photography inthe assessment of foot disordersALAN D. CRAXFORD, ALISON RUTHERFORD, MARTIN S. EVANS,AND COLIN PARK

From the University Departments of Orthopaedics, Photography and Surveying, Newcastle upon Tyne

SUMMARY Expanded polyethylene foam (Plastazote) is used in the treatment of rheumatoid,diabetic, and leprotic foot disorders. This paper describes a diagnostic use for this material. Twophotographic techniques combine to give vivid and quantitative representations of foot deformitieswhich are easily applicable to clinical use. Relief photography uses illumination to create anillusion of solidity in a 2-dimensional photograph. Stereophotogrammetry produces contour plotsfrom stereopairs of photographs of the Plastazote footprint. After use the impressions are trimmedand slipped into the patient's shoes in the same way as any other foam insole.

The footprint has been a basic research tool formany years both in medicine and in anthropologyand zoology. Studies of foot anatomy and patho-physiology have evolved in 2 distinct but interrelateddirections. The first investigates form and develop-ment in a static and often qualitative way, whereasthe second deals with the analysis of load and gaitdynamically. A list of some of these methods1-10is given in Table 1.

Clinically the information gained from inkedimprints on paper (Figs. IA, C, D) is simplistic,

Table 1 Methods ofanalysis ofplantar pressures

1. Sac filled with plaster-of-Paris Beely 1882

2. Combined rubber mat +glass plate Elftmann 1934

3. Inked fabric and rubber mat Morton 19354. Photograph from below

glass plate Harding 19425. Pressure transducers in

shoe sole Holden and Muncey 19536. Perspex rods and sponge

rubber Barnett 19547. Foam sock with pressure

crystals Brand 19638. Walkway with beam

galvanometers Stott, Hutton and Stokes 19739. Force plates and cine film Grundy et al. 1975

10. Liquid crystallography Scranton and McMaster 1976

and the procedure is messy for the operator andpatient alike. Pictures produced by mounting thecamera beneath a glass plate and photographingthe sole of the foot (Fig. IB) may be adequate todescribe form, but give little information about load,because the inflexibility of the glass deforms theplantar soft tissues. On the other hand the morecomplex forms of gait analysis are difficult to applyto the crippled patient in a clinical context andtherefore remain the province of the researchdepartment.

2% of the adult population complain of symptomsattributable to rheumatoid arthritis, and 85% ofthese will have foot problems some time during thecourse of their illness.'1 There is thus a continuingneed for a simple yet quantitative method of assess-ment of the development and progress of commonfoot deformities and of the results of surgical andconservative treatment.Expanded polyethylene foam (Plastazote) has

been used in clinical practice for some 10 years,firstly in the management of leprotic patients12 13and subsequently in the ambulant treatment oftrophic ulcers in the diabetic foot.14 In orthopaedicpractice it has a recognised place in the managementof rheumatoid metatarsalgia by producing custom-made total-contact insoles to fit surgical shoes.Consequently it was felt that the imprint of the footon such an insert could form the basis of a methodof assessment of deformity, the fabrication of whichhas already found patient acceptability and whichcould still be used in treatment after use.

83

Accepted for publication 25 February 1980Correspondence to Mr A. D. Craxford, University Depart-ment of Orthopaedics, Royal Victoria Infirmary, Newcastleupon Tyne.

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Fig. 1 Existing methods offootprinting. A. Harrisink mat. B. Sole of the foot photographed through aglass plate. C. Petroleum jelly footprint fluorescingunder ultraviolet light. D. Footprint from fingerprintpowder. These are from the same subject as in Fig. 2.

Materials and methods

PLASTAZOTE IMPRINT

Sheets of Plastazote i inch (20 mm) thick are used in

a standardised way to make the impression. This

involves placing the foot directly on the centre of thesheet, keeping the foot and ankle at a right-angle,

and asking the patient to look straight ahead. Thepatient takes full weight on each foot in turn,steadying his balance between 2 firm supports. Thecompleted impression is then subjected to 2 differentprocesses.

RELIEF PHOTOGRAPHThe insole is placed under the glass plate of astandard photographic copying table (in thisproject a Leitz Reprovit). The camera is mounteddirectly above the table, and the Plastazote isilluminated from one side only. The angle of inci-dence is 45°. Ilford 35 mm Pan F film is used,exposed for 7 seconds at an aperture of fI1 anddeveloped in Ilford Microphen for 41 minutes at230C (73°F). Monochrome emprints are producedwhich give the appearance of the foot in relief ratherthan as a depression.

STEREOPHOTOGRAMMETRIC RECORDStereophotogrammetry is the science of dimensionalanalysis of photographs using stereoscopic methodsand equipment. It is a standard procedure used byland surveyors in the preparation of topographicmaps from aerial photographs. The technique, whichis noninvasive, has been used in a number of appli-cations in medicine, orthopaedics, and oral surgery.15The Plastazote impression is photographed with a

stereometric camera. This comprises 2 identicalcameras of known inner orientation separated by aknown distance which produce a stereopair ofphotographs. Synchronisation is by electronic flash,which is used to improve illumination. EktachromeX colour reversal film is used for photography. Priorto exposure the impression is sprinkled with colouredconfetti to add texture to the uniform surface.

After processing the stereopair is orientated in aWild A7 stereoplotter to form a 3-dimensionalmodel of the footprint at a known scale. This is thenprobed with a measuring mark which can be movedby hand and foot controls in 3 mutually perpendi-cular directions relative to the model and whichcan be brought to rest on any point on its surface.Movement of the mark is linked to a drawing pencilwhich allows the plotting of contour lines to presenta graphical display of the shape of the footprint.The contour plots are produced lifesize and thecontour interval is 1 mm.

Results

REPRESENTATIVE ILLUSTRATIONSFig. 2 shows the relief photograph and stereophoto-grammetric plot of a normal foot. They demonstratethe expected pattern of pressure across the meta-tarsal heads with increased loading through the

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Stereophotogrammetry and reliefphotography in the assessment offoot disorders 85

hallux.1617 All 5 toes touch the ground, and thecontour lines indicate a well-developed arch.The appearance of the foot in a patient with

rheumatoid arthritis and localised metatarsalgia isshown in Fig. 3. There is soft tissue swelling over the

Fig. 2 Reliefphotograph of a normal foot, withstereophotogrammetric plot.

.. _ . .... : ~~~~~~~~~~~~~ , *( l.'

Fig. 3A. Photograph ofprolapsed metatarsal headswith concommitant dislocation of the metatarsophalangealjoints, with stereophotogrammetric plot.

Fig. 4A. Photograph ofa case of recurrent metatarsalgiafollowing forefoot arthroplasty, withstereophotogrammetric plot.

affected area and the metatarsal heads are prolapsedinto the sole. There is dorsal dislocation of thesecond and third metatarsophalangeal joints, whichis seen by the absence of an impression of therelevant toes. The abnormal loading across themetatarsal heads is plainly seen on the contour plot.

Fig. 4 shows a foot that has suffered from arecurrence of metatarsalgia some time after ap-parently successful surgery. All the metatarsalsare short, though the second one is relativelylonger than the rest and is markedly prominent. Thesite of abnormal weight bearing arises more proxi-mally in the sole than the symptoms suggest. Theinner 3 toes are functionless.

Discussion

Because Plastazote is already used in the treatmentof foot disorders, its use as a diagnostic tool in thisway does not require any alteration for its appli-cation to disabled patients. Some authorities haveobjected to the production of insoles directly fromthe foot,14 preferring to imprint the material with aplaster cast which allows the insole to be mouldedto the shape of the borders of the foot. However,this method requires a flat impression to produce themaximum weight-bearing deformity. There has beenno complaint of excessive heat in this series, whichso far includes over 300 footprints.The ability to see the sole of the foot in load is

invaluable in the clinical management of deformities,and the relief photograph provides the ideal method

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of storage of such information. The reason why theimage should be rendered as a relief remains unclear,but the illusion is highlighted by the use of sideillumination. The results are more dramatic andnatural in appearance than those from the ink mat,and the method is applicable in every hospital unit,as the equipment is readily available and inexpensive.Photogrammetric equipment on the other hand

is relatively expensive and requires the services of askilled operator. Consequently it is rarely availablein hospitals, but there are a number of organisationswhich can offer a service in this respect. Each contourplot takes about 1 hour to photograph and draw,and the outlay per patient compares favourably withroutine radiography.

These 2 procedures used in conjunction can pro-vide a graphic and quantitative picture of the staticfoot in load, and they are useful for making baselinepressure records before a course of treatment isembarked upon and for reviewing the results ofsurgery. They will delineate the extent of areas ofabnormal pressure which are of importance beforerevisional surgery is undertaken. Because the methodis noninvasive and easy to use, these procedures areinvaluable for illuminating the natural history ofthe deforming foot by repeated examinations over aperiod of time. They are also being used by thisresearch team in an endeavour to rationalise thedesign of surgical shoes.The impression is easily trimmed and buffed to

fit the patient's shoes to produce custom-made total-contact weight-bearing insoles once photographyhas been carried out. If this is not required, the sheetmay be reheated and used again.

This paper is based on an award-winning presentationgiven at the IXth European Congress of Rheumatology atWiesbaden, West Germany, September 1979.

The authors are indebted to Professor J. Stevens and DrW. Carson Dick, University Departments of Orthopaedicsand Rheumatology, for the advice in the preparation andrevision of the manuscript.

Plastazote is the registered trade mark of Messrs BakeliteXylonite Ltd, and is distributed for hospital use by MessrsT. J. Smith and Nephew, Welwyn Garden City, England.

References1 Beely F. Zur Mechanik des Stehens: Ober die Bedeitung

des Fussgewolkes beim Stehen. Langenbecks Arch Chir1882, 27: 457-68.

2 Elftmann H. A cinematic study of the distribution ofpressure in the human foot. Anat Rec 1934; 59: 481-7.Morton D. The Human Foot. New York: ColumbiaUniversity Press, 1935.Harding F R. Photographing the plantar surface of thefeet with weight bearing. J Biol Photographers Ass 1942;10: 113-5.Holden T S, Muncey R W. Pressures on the human footduring walking. Aust JAppl Sci 1953; 4: 405-9.

6 Barnett C H. A plastic pedograph. Lancet 1954; ii: 273.Bauman J H, Girling P W, Brand P. Plantar pressure andtrophic ulceration. J Bone Joint Surg 1963; 45B: 652-71.

8 Stott J R R Hutton W C, Stokes I A F. Forces under thefoot. J Bone Joint Surg 1973; 55B: 335-44.Grundy M, Tosh P A, McLeish R D, Smidt L. An investi-gation of the centres of pressure under the foot whilewalking. J Bone Joint Surg 1975; 57B: 98-103.

1 Scranton P E, McMaster J H. Momentary distributionof forces under the foot. J Biocmeh 1976; 9: 45-8.

1 Dixon A St J. The rheumatoid foot. Mod Trends Rheu-matol 1971; 2: 158-73.

12 Tuck W H. The use of Plastazote to accommodatedeformities in Hansen's disease. Lepr Rev 1969; 40: 171-3.

13 Mondl A M, Gardiner J, Bissett J. The use of Plastazotein footwear for leprosy patients. Lepr Rev 1969; 40: 177-81.

14 Hertzmann C A. Use of Plastazote in foot disabilities.Am JPhys Med 1973; 52: 289-303.

15 Herron R E. Stereophotogrammetry in biology andmedicine. Int Arch Photogrammetry 1972; 19: 5.

6 Acton R K. Surgical anatomy of the foot. J Bone JointSurg 1967; 49A: 555-67.

17 Harty M. Metatarsalgia. Surg Gynecol Obstet 1973;136: 105.

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