Ofthotic prescription processfor the diabetic foot WilliamMunro A RT I CLE P O I N T S 1I A matrix of I possibilitiescan be establishedto guide efforts to optimise treatment. ^l There are three main t L opttonsfor shoes: stock shoes.modular shoesand bespoke shoes. a Aharmonious J combinationof foot orthoses and footwear will ensureoptimised treatment. 1l Therc is a &f considerablevariety of healing footwear available for both forefoot and hind foot relief. A rational approach < J to the prescription of orthosesand shoesfor the diabetic foot is essential. KEY WORDS o Prescription e Footwear r Orthoses o Rockers
WilliamMunro is a Clinical Associate at the National Centre for Trainingand Educationin Prostheticsand Orthotics (NCTEPO), Universityof Strathclyde.
ootwear should be providedon the basis of verified clinical need. A m a tri x o f possi bi l i ti es can be establishedto guide efforts to optimise treatment. This matrix should be constructedusingthe following criteria. l) Deformity Deformity can be classifiedas 'significant' or 'non-significant'. The author'sdefinition of significantdeformity is related to the mechanicalalignmentof the foot with the heel,balland toe aspectsof a normalshoe. lf the foot does not line up within these shoe parameters there will be potential friction, shearand pressureimplicationsand the deformity will be 'significant'. An example of a significantdeformity is shown in Figure/. RigidPesCavus,with an obvious retraction of the toes, creates a situationin which the forefoot from the ball to toe end is not in balance.Consequently, when the individualwalks,the author has observedthat inadequatetoe depth in the toe-off phase of gait will result in an i n c re a s e i n p l antar pressure on the metatarsalheads.lt may also leadto dorsal p re s s u re fro m tw i sti ng i n the upper materialof the shoe. 'Non-significant' deformity relates to a foot that hasmechanicalalignmentwith the heel, ball and toe end of the shoe, but which has hammer toes, hallux valgusor other manageable biomechanical anomalies.
2) Ambulatory status It is important to assessthe magnitudeand type of ambulatory ability.This has been observed to range from an occupationally active level to one of sedentarydisability. The durability and effectiveness of footwear and foot orthoseswill dependon the wear during activity. 3) Biomechanical analysis The extent of deformity is very often linked to the adversebiomechanics found at the talo-crural,sub-talarand mid-tarsaljoints. The concept of what is hoped to be achievedcan be conveyedwith an intuitive biomechanical analysis, as detailedbelow. In the author'sopinion,it is importantto recognise the relationship between the hind foot and forefoot in the three main phasesof the gait cycle.The foot complex can be likenedto a stablethree-pegmilking stool in mid-stance,where the sub-talar joint is neutral and the mid-tarsaljoint is maximally pronated (Figure 2). Any deviationfrom this will resultin an unstable mechanicalfoot structure. lf the forefoot is hypermobilethrough excessof pronation, it is necessaryto realignthe foot to allow the plantar plane of the forefoot to be parallelwith the plantarplaneof the hind foot. This can be achieved orthotically through posting. lf the forefoot is supinatedand rigidity is a factor, the orthotic accommodation is
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Figure 1. An example of a deformity judged as signfficunt: Rigid Pes Cavus.
required in the form of a cradle. By returning the foot to a stable, mechanical state, pressureredistribution is optimised, thereby reducingpressureand shear. 4) Neuropathic status The extent of neuropathy is normally determined at an annual screening.This screening may use different methods to quantify the outcome; however,the main factor is the loss of protective sensation, as assessedusing a l0S monofilament and a Neurotip: (Owen Mumford, Woodstock). The loss of protective sensationconsiderablyincreasesthe risk of breakdown from friction and shear force between foot and shoe and must be taken into account when formulating a prescription. 5) lschaemic status The vascularstatus is also determined at the annual screening,and this too has a bearing on risk of breakdown and tissue viability (Chantelauet al, 1990; Edmonds and Foster,2005). Capillary refill time and the status of dorsalis pedis and the posterior tibial pulseare the main clinical indicatorshere.
I '
Figure 2. A'milking stool' model of parts of the foot complex (adapted from Rose,
1e86).
ffi
6) Environment Consideration of the foot's environment covers a number of potential areas of concern.As a result of leather production processes,an allergy to chrome tanning may be an issueand shouldbe dealtwith by the use of vegetabletanning.The use of latex and rubber solutions may also pose some difficultiesand avoidingthese would require the hand sewingof the sole to the upper during shoe manufacture. In addition, the prevailingelementsthat the patients are exposed to in terms of climate and terrain must be consideredin view of fitnessto purposeand durability. Using a matrix of these factors allows for individual patients' circumstancesto be taken into account and optimises the rationale for prescription of the most suitableform of footwear.
Options for shoes There are three mainoptionsto choosefrom: o stock shoes o modularshoes o bespokeshoes. Stock shoes Stock shoes currently account for some 70% of prescri bed shoes ( Audit Commission, 2000) and can offer a mechanically viablesolutionaswell as being ly acceptable. cosmetical The important features of stock shoes are the correct width, depth and lengthsas set out by the individualmanufacturers,as well as the designfeaturesof materialsand pattern shapes.Foot orthoses should be manufacturedwith shoe compatibility in mind to ensureoptimisedfunction.Model styles should avoid rims and seams at vulnerableareas,such as the medialaspect joint. of the first metatarsalphalangeal ln some designs of stock shoes the weight or thicknessof the leather used can sometimesbe too lightfor the task it hasto perform. This resultsin an over-torquingof the upper on the solethat then givesrise to a badly misshapenshoe that may result in trauma to the foot. Modular shoes Modular shoes offer a mid-way point
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c Figure 3. Features of a shoe (A : rim toe puffi B : vampl C : luteral edge; D : nylon strip; E : padded collar).
between stock shoes and bespoke shoes. This is usuallyachievedby usinga stock last and style, and then adding extra features s u c h a s b u i l d -ups over j oi nts, w i dth variancesat joints and heels, and specific toe depth build-ups.These extra features may also be added at a 'rough fitting' stage to facilitatemore intimatefit solutions. Bespoke shoes Up until the mid-1980s,bespokewas the only way that footwear was produced for patients.The technique for measurement and production was based on a standard (BS 5943) of the British Standards Institution ( 1980).Manufacturingwas, and still is, largelycentred on the hand skillsof craftsmen.ln the author'sexperience,only recently have computer-aideddesign and manufacturing systems started to play a
Figure 4. Examples offoot orthoses.
greater role in footwear production and design(wherebya foot is scanned,the scan is analysedand the result is downloaded onto the machinefor manufacture). The greatest challenge in producing bespoke footwear is how to transfer complicated foot shapes from a twodimensionalset of measurements to a threedimensionalshoe form in a cosmetically and functionally acceptable way Careful, methodicalmeasurementis a fundamental prerequisitefor accuratemanufactureand a ry fit functionallysatisfacto It is believedthat this is where most of the challengesthat create criticism of arise from. bespoke shoes will Inappropriate facilities for measurement and consultation,coupled with inadequate consultationtimes, exacerbatethe needfor the extreme concentration required to produce what is a precise technical specification.The measurementstaken should be to the standardthat would be expected of a surveyor. scannersmay The use of computer-based help producemore accuratemeasurements over time. However,the handskillsrequired to judge, for example, the density or pliability of a fatty heel pad and the extent that it might distort to produce shear can only be done by someone who has the experience,skill and knowledgeto do so. The benefit of bespokeshoes should be their abilityto optimisetreatmentoptionsin a way that ensuresmaximum protection for an at-risk foot. This meansthat every aspect of shoe designcan be taken into accountand accuracy of placement of features such as windows, rockers and tab points can be considered.(Windows are holes cut in the core material of the cradle or functional device;rockersare explainedin more detail below; and tab points are the points where eyeletsor velcro strapsare attached.) In the bespoke shoe, the weight and density of the upper can be more closely control l ed, and the durabilit y of sole materials and their construction can be tuned to suit the data collected from subsequentreviews. In the author's opinion - whether stock, modularor bespokefootwear is indicatedconsensus over the years has dictated certain features (e.g. Tovey and Moss,
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Figure 5. Forefoot Relief shoe (eft) und Heel Relief shoe (right; IPOS, Kennesaw, GA).
1984), and the basis for a good diabetic shoe should have the following features (Figure3): o rim toe puff (A) O upper and liningweight over vamp (B) of b e tw e e n4 a n d 8U m o lateral edge (C) that is straighter from waist to toe end o tabs that have a nylon strip (D) between the liningand the upper to facilitatea gap between the tabs of approximately 1 . 5c m o properly padded collars (E) to protect the distal aspects of the malleoli and Achillestendon o leatheror plushlinings,and not synthetic liningsthat may fray and become brittle. From these factors, appropriate prescription of footwear will follow a logicalsequence'andallow for recognition of a spectrumof activitythat will matchthe patient'sclinicalneed. As s e s s me n t of i ndi vi dual spoi nts to their place on the prescription matrix and therefore indicates the functional requirements for foot orthoses and particular adaptations. The functional requirements,in turn, point to the style and designpossibilities. Although cosmesis is important and recent manufacturing approacheshave improved the range of design possibilities,function is still the primary driver of shoe design. Certain featuressuchas rocker soleswill be required for some patients when indicatedby the prescriptionmatrix, but it is not a fundamentalrequirement for all diabetic shoes to have a rocker sole. Patientswho haveneuropathywith minimal
biomechanical anomalyand who are at risk do not require footwear with the same designfeaturesas patientswho haveplantar ulcerationand significant deformity.
Foot orthoses The challenge for footwear and foot orthoses is a mechanicalone that requires the management of several factors: the interfacesbetweenground, shoe sole, foot orthoses, skin and then bone (Pratt and Tollafield,199n.A harmoniouscombination of foot orthoses and footwear will then ensure optimised treatment, whether the device is for prophylaxis or for maintenanceof a previouslyulceratedfoot. It is thereforevital that, in the first instance, the interface between the foot and the shoe is designedto meet the needsof not only the foot but the vehiclethat carriesit. The manufactureof ficot orthoses,too, is relatedto the function of the individualfeet that are beingexamined.Materialchoicesare centred on supportivefunction, stabilisation or accommodationof deformities, relief of excessive plantar pressure, reduction of pressure and shear, and the possible limitation of range of motion. Examplesof foot orthoses are shown in Figure4. To facilitate the accurate manufactureof the orthoses it is necessaryto have a repeatablepatient casting procedure that allows for control or manipulationof the lower limb complex and optimises the biomechanicalevaluations(Janisse,| 993). Appropriate material choice is vital. By applying Newtonian mechanics to the designprinciplesinitiallyoutlined by Tovey ( 1983)for usein Hansen'sdisease, changing the core material from high-density plastazote to medium-density EVA prevented the structural distortion that was often a problem after a short period of use. Consequently, Nora (Algeos, Liverpool) rubber shoe componentsare a good substitute for EVA; however, the pati ent' s mass and bi ome chanicswill ultimatelybe the decidingfactor. Top cover materialssuchas Poron (Rogers Corporation, Woodstock, CT) may be adopted, while Diabet bedding material (Algeos, Liverpool) can be used depending on the skin viability or the density of neuropathy.The author believesthat Poron
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94 makesa very good substancefor pressure reliefwindows,superseding injectedsilicone or Dunlopillow(Algeos,Liverpool).
Figare 6. A pressurerelieving ankle foot orthosis (PRAFO).
Rockers It is the author's opinion that rockers (Figure 5), where required, should be constructed as part of foot orthoses - a follow-through rocker using carbon fibre may be addedto the outer sole to maintain the harmonisation of the required mechanicaleffect. lt allows for a more cosmetic effect on the footwear, especially when combinedwith a throughsole,which givesa wedge look to the shoe. lt also acts as a torque converter to the sole. Much hasbeen written about rockers and their effectiveness(e.g.Schaffand Cavanagh, 1990).The baseprincipleis the shortening of the lever arm,that allowsfor the change in the timing,magnitudeand direction,with respect to the foot, of the gr.oundreaction force over time. During the normal gait cycle,the ground reaction force has a point of theoreticalapplicationcloseto the heelat initial contact of the limb in stance phase. This point of application,often termed the 'centre of pressure',moves forward on the foot as the gait cycle progresses. The position and magnitudeof a rocker will haveinfluencefrom mid-stanceonwards to toe-off on the stance limb. Moving the position of the rocker posteriorly will shorten the stancephaseand not allow the centre of pressure to advancebeyond the rocker. This will have a protective effect if the metatarsalheadsor areasof the foot at risk are anterior to the rocker: The relative height of the rocker will also influencethe effectivetiming and duration of the stance phaseof gait. It is important to remember that modificationssuch as a rocker are madeto the shoe,and the relationshipbetweenthe shoe and the foot will need to be specified unambiguously if the impactof the rocker is to be recorded in a controllableway. This has to be achieved, the author believes,on an individualbasis,taking into account the size and biomechanicsof the individualfoot and the magnitudeof the rocker required. Plantar pressureschange accordingto how far behindthe metatarsal heads the rocker is placed and what the
effectivedistanceof the metatarsalheadsis from the fulcrum of the rocker. The author hasfoundthat if l0' of rocker helpsto heala forefoot plantarulcer,then it is good to build this amount of rocker into the foot orthoses of the footwear made to maintainthe foot after healing.The upper limit for a rocker would be 30 o, as this, in practice,meansan unsightlyand somewhat unstablelevel to maintainthat would also require a compensatoryraiseon the contralateralside. The heel height and pitch of a shoe are very important as well, becausea shoewith a heel heightin excessof 2.5 cm and a pitch angleof over 30 " will result in an increase in weight on the metatarsalheads.This, in turn, will have a negativeinfluenceon the actionsof the foot orthoses. Additional orthoses that aid prevention and healing There is a considerablevariety of healing footwear availablefor both forefoot and hind foot relief. Where feet are dressed and bandaged and lesions are on the margins or dorsal aspect, a trauma shoe with a standard heel height and pitch should be used. On too many occasions, the author has found, secondarytrauma is initiated by the incorrect use of fracture cast shoes that are rockered in the midfoot and subsequentlytransfer pressureto an inappropriateplace. Forefoot relief shoes come in varieties with no forefoot plantar protection and those with a follow-through sole. The advantageof the exposed forefoot is that there is no plantar pressureon the wound site; however, the patient has to be very careful not to traumatise the exposed area further. All of these shoes havea rocker to l0 o, and, as previouslystated,this degree of rocker should form the basis of any deviceonce healinghas been achieved.lt is also possibleto customisea foot orthosis to a shoe with a full sole to facilitate optimised pressure redistribution. Hind foot relief shoes should be used in conjunctionwith a pressure-relieving ankle foot orthosis (PRAFO)at the rehabilitation phaseof treatment as daytimeoff-loadingis nullifiedif recumbentrelief is not used. PRAFOs(Figure5) should be used in the
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ORTHOTIC PRESCRIPTION PROCESSFOR THE DIABETIC FOOT
Figure 7. An Aircast walker.
Conflict of interest The author, along with Dr Derek Jones,was responsiblefor bringing pressure-relieving ankle foot orthoses (PRAFOs)into use in the UK, and is now associated with the rnarketing of PMFOs for the company Anatomical Concepts (UK) Ltd.
prevention and treatment of distal posterior border lesionsof the heel and for lesionson the medialand lateralaspectsof the hind foot and the malleoli. To maximisethe treatment potential it is important to use the device in both recumbentand ambulatorymodalities.The configurationand designof these devicesis paramount to the safety and efficacy of their use. In a retrospective study of three major heelwound outcomes(Munro et al, 2005). it was found that maintainingthe foot in a dorsiflexed position with a stable metal upright that resisted plantar flexion, in addition to the wound site being totally pressure-relieved, was a major benefit to healing. The ability to walk with no pressure on the wound and have a heel strike enhancedthe secondary calf-pump m e c h a n i s m and al l ow ed an opti mum physiological state to be maintained. In the author'sopinion,the PRAFOsAPU and Dual Action (Anatomical Concepts, Clydebank) have the versatility and durability to allow these functions to be performed. Devices that are made of preformed contoured polypropylene are useful only in recumbent situations and great care should be taken to monitor deterioration of the plastic,which can lead to plantar flexion of the foot with resultant increasesin forefoot plantar pressure. The use of Aircast walkers (Aircast, Summit,NJ;Figure7) is now widespreadand not without some controversy (based on the author's experience of a recent conference).The author believesthat it is an extremely usefuldeviceif customisedto the individualpatient and that it can satisrythe need ficr immediate immobilisationof an early-stageCharcot foot. The ability to use the air cells for graduated compression allows oedema control to take place safely with little chanceof tissue damage.The use of a customisedfoot bed further enhances the plantar pressurerelief role. Howeve[ it must be stressed that a high degree of patient educational input is the key to successfulsafeuse,and in the early stagesof use frequent follow-up and counsellingis desirable. Bespokeplastic or carbon fibre devices can also achieveaxialoff-loading;thesemay
also be described as a Charcot Restraint Orthotic Walker (CROW; Edmondset al, 2004). The design and fit is specificto the needsof the patient,althoughthese devices should alwayshave a full foot plate and be suitablypaddedto protect tissueviability. Conclusions A rational approachto the prescriptionof orthoses and shoesfor the diabeticfoot is essential.A matrix of treatment strategies has been presented. Use of this allows patient need and level of risk to be orthotically matched to ensure optimised preventionor healing. Shoe design and manufacture and orthoses need to be considered both individuallyand collectively.A harmonious combination of foot orthosis and shoe is required both for function and cosmetics. Educationand counsellingis also very important. The clinical and psychological expectationsof patientsand the clinicteam I haveto be met. Acknowledgment Dr DerekJones,a friend and colleagueof the author, provided support and advice in reviewingthis article.
Audit Commission (2000) Fully Equipped report on prostheilc and orthotic seryices.Audit Commission Publications,Wetherby British Standards lnstitution ( 1980) Methods for Measurementand Recordingfor OrthopaedicFootweor
(BSse43)
Chantelau E, Kushner T, Spraul M ( 1990) How effective is cushioned therapeutic footwear in protecting diabetic feet. Diobetic Medicine 7(4): 355-9 Edmonds ME, Foster AVM (2005) Monoging the DiobeticFootZnd edition. BlackwellScience,Oxford Edmonds ME, Foster AVM, SandersL (2004) Prodical Monuol of Diabetic Foot Care. Blackwell Science, Oxford JanisseDJ ( 1993)A scientificapproachto insoledesign for the diabetic foot. The Foot 3(3): 105-8 Munro WA, Jones Q Stang D Benbow S (2005) Clinical experience of the PRAFO in the management of the diabetic foot. Allied Health ProfessionsClinicolEflbctivenessMeeting,Scotland Pratt DJ, Tollafield DR (1997) An introduction to mechanical therapeutics. ln: DR Tollafield, LM Merriman, eds. Clinicol Skills in Treoting the Foot Churchill Livingstone,London Rose GK (1986) Orthotics: principles ond procilce. HeinemannMedicalBooks, London Schaff PS, Cavanagh PR (1990) Shoes for the insensitive foot the effect of a "rocker bottom" shoe modification on plantar pressure distribution. Footond Ankle I l(3): 129-40 Tovey Fl ( 1983)Method of healingdiabeticfoot ulcers. BritishMedicolJournal 286(6367): 805 Tovey Fl, Moss MJ (1984) Manufacturing diabetic footwear. Core, Scienceond Prodice4(2): l7-2
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