Ofthotic prescription process for thediabetic foot

Wil l iam Munro

ARTICLE POINTS

1 A matrix ofI

I possibil i t ies can beestablished to guideefforts to optimisetreatment.

^l There are three maint

L opttons for shoes:stock shoes. modularshoes and bespokeshoes.

a AharmoniousJ combination of footorthoses and footwearwill ensure optimisedtreatment.

1l Therc is a&f considerable varietyof healing footwearavailable for bothforefoot and hind footrelief.

< A rational approachJ to the prescription oforthoses and shoes forthe diabetic foot isessential.

KEY WORDSo Prescriptione Footwearr Orthoseso Rockers

Wil l iam Munro is a Cl in icalAssociate at the National Centrefor Training and Education inProsthetics and Orthotics(NCTEPO), University ofStrathclyde.

ootwear should be provided on thebasis of verif ied clinical need. Amatr ix of possibi l i t ies can be

established to guide efforts to optimisetreatment. This matrix should beconstructed using the following criteria.

l) DeformityDeformity can be classified as 'significant'

or 'non-significant'. The author's definit ionof significant deformity is related to themechanical alignment of the foot with theheel, ball and toe aspects of a normal shoe.lf the foot does not l ine up within theseshoe parameters there will be potentialfriction, shear and pressure implications -

and the deformity will be 'significant'.

An example of a significant deformity isshown in Figure /. Rigid Pes Cavus, with anobvious retraction of the toes, creates asituation in which the forefoot from the ballto toe end is not in balance. Consequently,when the individual walks, the author hasobserved that inadequate toe depth in thetoe-off phase of gait will result in anincrease in plantar pressu re on themetatarsal heads. lt may also lead to dorsalpressure f rom twist ing in the uppermaterial of the shoe.

'Non-significant' deformity relates to afoot that has mechanical alignment with theheel, ball and toe end of the shoe, butwhich has hammer toes, hallux valgus orother manageable biomechanical anomalies.

2) Ambulatory statusIt is important to assess the magnitude andtype of ambulatory ability. This has beenobserved to range from an occupationallyactive level to one of sedentary disability.The durabil ity and effectiveness offootwear and foot orthoses will depend onthe wear during activity.

3) Biomechanical analysisThe extent of deformity is very often linkedto the adverse biomechanics found at thetalo-crural, sub-talar and mid-tarsal joints.

The concept of what is hoped to beachieved can be conveyed with an intuitivebiomechanical analysis, as detailed below.

In the author's opinion, it is important torecognise the relationship between thehind foot and forefoot in the three mainphases of the gait cycle. The foot complexcan be l ikened to a stable three-peg milkingstool in mid-stance, where the sub-talarjoint is neutral and the mid-tarsal joint

is maximally pronated (Figure 2). Anydeviation from this wil l result in an unstablemechanical foot structure. lf the forefoot ishypermobile through excess of pronation,it is necessary to realign the foot to allowthe plantar plane of the forefoot to beparallel with the plantar plane of the hindfoot. This can be achieved orthoticallythrough posting.

lf the forefoot is supinated and rigidity isa factor, the orthotic accommodation is

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ORTHOTIC PRESCRIPTION PROCESS FOR THE DIABETIC FOOT

I '

Figure 1. An exampleof a deformity judged assignfficunt: Rigid Pes Cavus.

Figure 2. A'milking stool'model of parts of the footcomplex (adapted from Rose,1e86).

required in the form of a cradle. Byreturning the foot to a stable, mechanical

state, pressure redistribution is optimised,

thereby reducing pressure and shear.

4) Neuropathic statusThe extent of neuropathy is normallydetermined at an annual screening. This

screening may use different methods toquantify the outcome; however, the main

factor is the loss of protective sensation,

as assessed using a l0S monofilament

and a Neurotip: (Owen Mumford,

Woodstock). The loss of protective

sensation considerably increases the risk of

breakdown from friction and shear forcebetween foot and shoe and must betaken into account when formulating aprescription.

5) lschaemic statusThe vascular status is also determined at

the annual screening, and this too has a

bearing on risk of breakdown and tissue

viabil ity (Chantelau et al, 1990; Edmonds

and Foster, 2005). Capillary refill time andthe status of dorsalis pedis and theposterior t ibial pulse are the main clinicalindicators here.

6) Environment

Consideration of the foot's environmentcovers a number of potential areas of

concern. As a result of leather production

processes, an allergy to chrome tanning

may be an issue and should be dealt with by

the use of vegetable tanning. The use of

latex and rubber solutions may also pose

some difficulties and avoiding these wouldrequire the hand sewing of the sole to the

upper during shoe manufacture.

In addition, the prevailing elements that

the patients are exposed to in terms of

climate and terrain must be considered in

view of fitness to purpose and durability.

Using a matrix of these factors allows for

individual patients' circumstances to be

taken into account and optimises the

rationale for prescription of the most

suitable form of footwear.

Options for shoesThere are three main options to choose from:

o stock shoes

o modular shoes

o bespoke shoes.

Stock shoesStock shoes currently account for some

70% of prescr ibed shoes (Audi t

Commission, 2000) and can offer a

mechanically viable solution as well as being

cosmetical ly acceptable.The important features of stock shoes

are the correct width, depth and lengths as

set out by the individual manufacturers, aswell as the design features of materials andpattern shapes. Foot orthoses should bemanufactured with shoe compatibility inmind to ensure optimised function. Model

styles should avoid rims and seams atvulnerable areas, such as the medial aspect

of the first metatarsal phalangeal joint.

ln some designs of stock shoes theweight or thickness of the leather used cansometimes be too light for the task it has toperform. This results in an over-torquing ofthe upper on the sole that then gives rise to

a badly misshapen shoe that may result in

trauma to the foot.

Modular shoesModular shoes offer a mid-way point

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ORTHOTIC PRESCRIPTION PROCESS F'OR THE DIABETIC FOOT

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 usually achieved by using a stock last

and style, and then adding extra features

such as bui ld-ups over jo ints, width

variances at joints and heels, and specific

toe depth build-ups. These extra featuresmay also be added at a 'rough fitting' stage

to facilitate more intimate fit solutions.

Bespoke shoes

Up until the mid- 1980s, bespoke was theonly way that footwear was produced forpatients. The technique for measurement

and production was based on a standard(BS 5943) of the Brit ish StandardsInstitution ( 1980). Manufacturing was, and

still is, largely centred on the hand skills of

craftsmen. ln the author's experience, onlyrecently have computer-aided design and

manufacturing systems started to play a

Figure 4. Examples offootorthoses.

greater role in footwear production and

design (whereby a foot is scanned, the scan

is analysed and the result is downloaded

onto the machine for manufacture).

The greatest challenge in producing

bespoke footwear is how to transfer

complicated foot shapes from a two-

dimensional set of measurements to a three-

dimensional shoe form in a cosmetically

and functionally acceptable way Careful,

methodical measurement is a fundamentalprerequisite for accurate manufacture and a

functionally satisfacto ry fit

It is believed that this is where most of

the challenges that create crit icism of

bespoke shoes wil l arise from.

Inappropriate facilities for measurement

and consultation, coupled with inadequate

consultation times, exacerbate the need for

the extreme concentration required to

produce what is a precise technical

specification. The measurements taken

should be to the standard that would be

expected of a surveyor.The use of computer-based scanners may

help produce more accurate measurements

over time. However, the hand skills required

to judge, for example, the density orpliability 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 knowledge to do so.

The benefit of bespoke shoes should be

their ability to optimise treatment options in

a way that ensures maximum protection for

an at-risk foot. This means that every aspect

of shoe design can be taken into account and

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; rockers are explained in more detail

below; and tab points are the points where

eyelets or velcro straps are attached.)In the bespoke shoe, the weight and

density of the upper can be more closely

control led, and the durabi l i ty of sole

materials and their construction can be

tuned to suit the data collected from

subsequent reviews.

In the author's opinion - whether stock,

modular or bespoke footwear is indicated -

consensus over the years has dictated

certain features (e.g. Tovey and Moss,

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ORTHOTIC PRESCRIPTION PROCESS FOR THE DIABETIC FOOT

Figure 5. Forefoot Reliefshoe (eft) und Heel Reliefshoe (right; IPOS, Kennesaw,GA).

1984), and the basis for a good diabeticshoe should have the following features(Figure 3):o rim toe puff (A)

O upper and lining weight over vamp (B) ofbetween 4and 8Um

o lateral edge (C) that is straighter fromwaist to toe end

o tabs that have a nylon strip (D) betweenthe lining and the upper to facilitate a gapbetween the tabs of approximately1 . 5 c m

o properly padded collars (E) to protectthe distal aspects of the malleoli andAchil les tendon

o leather or plush l inings, and not syntheticlinings that may fray and become brittle.From these factors, appropriate

prescription of footwear will follow alogical sequence'and allow for recognitionof a spectrum of activity that will match thepatient's clinical need.

Assessment of indiv iduals points totheir place on the prescription matrixand therefore indicates the functionalrequirements for foot orthoses andparticular adaptations. The functionalrequirements, in turn, point to the styleand design possibil i t ies. Although cosmesisis important and recent manufacturingapproaches have improved the range ofdesign possibil i t ies, function is sti l l theprimary driver of shoe design.

Certain features such as rocker soles willbe required for some patients whenindicated by the prescription matrix, but itis not a fundamental requirement for alldiabetic shoes to have a rocker sole.Patients who have neuropathy with minimal

biomechanical anomaly and who are at riskdo not require footwear with the samedesign features as patients who have plantar

ulceration and signifi cant deformity.

Foot orthosesThe challenge for footwear and footorthoses is a mechanical one that requiresthe management of several factors: theinterfaces between ground, shoe sole, footorthoses, skin and then bone (Pratt andTollafield, 199n. A harmonious combinationof foot orthoses and footwear will thenensure optimised treatment, whetherthe device is for prophylaxis or formaintenance of a previously ulcerated foot.It is therefore vital that, in the first instance,the interface between the foot and theshoe is designed to meet the needs of notonly the foot but the vehicle that carries it.

The manufacture of ficot orthoses, too, isrelated to the function of the individual feetthat are being examined. Material choices arecentred on supportive function, stabilisationor accommodation of deformities, relief ofexcessive plantar pressure, reduction ofpressure and shear, and the possiblelimitation of range of motion. Examples offoot orthoses are shown in Figure 4.

To facilitate the accurate manufacture ofthe orthoses it is necessary to have arepeatable patient casting procedure thatallows for control or manipulation of thelower l imb complex and optimises thebiomechanical evaluations (Janisse, | 993).

Appropriate material choice is vital. Byapplying Newtonian mechanics to thedesign principles initially outlined by Tovey( 1983) for use in Hansen's disease, changingthe core material from high-densityplastazote to medium-density EVAprevented the structural distortion thatwas often a problem after a short periodof use. Consequently, Nora (Algeos,

Liverpool) rubber shoe components are agood substitute for EVA; however, thepat ient 's mass and biomechanics wi l lultimately be the deciding factor.

Top cover materials such as Poron (RogersCorporation, Woodstock, CT) may beadopted, while Diabet bedding material(Algeos, Liverpool) can be used dependingon the skin viability or the density ofneuropathy. The author believes that Poron

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ORTHOTIC PRESCRIPTION PROCESS FOR THE DIABETIC FOOT

Figare 6. A pressure-relieving ankle foot orthosis(PRAFO).

94 makes a very good substance for pressurerelief windows, superseding injected siliconeor Dunlopillow (Algeos, Liverpool).

Rockers

It is the author's opinion that rockers(Figure 5), where required, should beconstructed as part of foot orthoses - afollow-through rocker using carbon fibremay be added to the outer sole to maintainthe harmonisation of the requiredmechanical effect. lt allows for a morecosmetic effect on the footwear, especiallywhen combined with a through sole, whichgives a wedge look to the shoe. lt also actsas a torque converter to the sole.

Much has been written about rockers andtheir effectiveness (e.g. Schaff and Cavanagh,1990). The base principle is the shorteningof the lever arm,that allows for the changein the timing, magnitude and direction, withrespect to the foot, of the gr.ound reactionforce over time. During the normal gaitcycle, the ground reaction force has a pointof theoretical application close to the heel atinitial contact of the limb in stance phase.This point of application, often termed the'centre of pressure', moves forward on thefoot as the gait cycle progresses.

The position and magnitude of a rockerwill have influence from mid-stance onwardsto toe-off on the stance limb. Moving theposition of the rocker posteriorly willshorten the stance phase and not allow thecentre of pressure to advance beyond therocker. This will have a protective effect ifthe metatarsal heads or areas of the foot atrisk are anterior to the rocker: The relativeheight of the rocker will also influence theeffective timing and duration of the stancephase of gait.

It is important to remember thatmodifications such as a rocker are made tothe shoe, and the relationship between theshoe and the foot will need to be specifiedunambiguously if the impact of the rocker isto be recorded in a controllable way.

This has to be achieved, the authorbelieves, on an individual basis, taking intoaccount the size and biomechanics of theindividual foot and the magnitude of therocker required. Plantar pressures changeaccording to how far behind the metatarsalheads the rocker is placed and what the

effective distance of the metatarsal heads isfrom the fulcrum of the rocker.

The author has found that if l0' of rockerhelps to heal a forefoot plantar ulcer, then itis good to build this amount of rocker intothe foot orthoses of the footwear made tomaintain the foot after healing. The upperlimit for a rocker would be 30 o, as this, inpractice, means an unsightly and somewhatunstable level to maintain that would alsorequire a compensatory raise on the contra-lateral side.

The heel height and pitch of a shoe arevery important as well, because a shoe witha heel height in excess of 2.5 cm and a pitchangle of over 30 " will result in an increasein weight on the metatarsal heads. This, inturn, will have a negative influence on theactions of the foot orthoses.

Additional orthoses that aidprevention and healing

There is a considerable variety of healingfootwear available for both forefoot andhind foot relief. Where feet are dressedand bandaged and lesions are on themargins or dorsal aspect, a trauma shoewith a standard heel height and pitchshould be used. On too many occasions,the author has found, secondary trauma isinitiated by the incorrect use of fracturecast shoes that are rockered in the mid-foot and subsequently transfer pressure toan inappropriate place.

Forefoot relief shoes come in varietieswith no forefoot plantar protection andthose with a follow-through sole. Theadvantage of the exposed forefoot is thatthere is no plantar pressure on the woundsite; however, the patient has to be verycareful not to traumatise the exposed areafurther. All of these shoes have a rocker tol0 o, and, as previously stated, this degreeof rocker should form the basis of anydevice once healing has been achieved. lt isalso possible to customise a foot orthosisto a shoe with a full sole to facilitateoptimised pressure redistribution. Hindfoot relief shoes should be used inconjunction with a pressure-relieving anklefoot orthosis (PRAFO) at the rehabilitationphase of treatment as daytime off-loading isnullified if recumbent relief is not used.

PRAFOs (Figure 5) should be used in the

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ORTHOTIC PRESCRIPTION PROCESS FOR THE DIABETIC FOOT

Figure 7. An Aircast walker.

Conflict of interestThe author, along with Dr Derek

Jones, was responsible for bringingpressure-relieving ankle footorthoses (PRAFOs) into use in theUK, and is now associated withthe rnarketing of PMFOs for thecompany Anatomical Concepts(UK) Ltd.

prevention and treatment of distalposterior border lesions of the heel and forlesions on the medial and lateral aspects ofthe hind foot and the malleoli.

To maximise the treatment potential it is

important to use the device in both

recumbent and ambulatory modalities. The

configuration and design of these devices isparamount to the safety and efficacy oftheir use.

In a retrospective study of three major

heel wound outcomes (Munro et al, 2005).

it was found that maintaining the foot in adorsiflexed position with a stable metal

upright that resisted plantar flexion, in

addition to the wound site being totallypressure-relieved, was a major benefit tohealing. The abil ity to walk with nopressure on the wound and have a heel

strike enhanced the secondary calf-pumpmechanism and al lowed an opt imumphysiological state to be maintained.

In the author's opinion, the PRAFOs APU

and Dual Action (Anatomical Concepts,

Clydebank) have the versati l i ty and

durability to allow these functions to beperformed. Devices that are made ofpreformed contoured polypropylene areuseful only in recumbent situations andgreat care should be taken to monitordeterioration of the plastic, which can lead

to plantar flexion of the foot with resultantincreases in forefoot plantar pressure.

The use of Aircast walkers (Aircast,

Summit, NJ; Figure 7) is now widespread andnot without some controversy (based onthe author's experience of a recentconference). The author believes that it is an

extremely useful device if customised to theindividual patient and that it can satisry theneed ficr immediate immobilisation of an

early-stage Charcot foot. The ability to usethe air cells for graduated compressionallows oedema control to take place safely

with little chance of tissue damage. The use

of a customised foot bed further enhancesthe plantar pressure relief role. Howeve[ it

must be stressed that a high degree ofpatient educational input is the key tosuccessful safe use, and in the early stages ofuse frequent follow-up and counselling isdesirable.

Bespoke plastic or carbon fibre devices

can also achieve axial off-loading;these may

also be described as a Charcot Restraint

Orthotic Walker (CROW; Edmonds et al,

2004). The design and fit is specific to theneeds of the patient, although these devices

should always have a full foot plate and besuitably padded to protect tissue viability.

Conclusions

A rational approach to the prescription oforthoses and shoes for the diabetic foot is

essential. A matrix of treatment strategies

has been presented. Use of this allowspatient need and level of risk to beorthotically matched to ensure optimisedprevention or healing.

Shoe design and manufacture and

orthoses need to be considered bothindividually and collectively. A harmonious

combination of foot orthosis and shoe is

required both for function and cosmetics.Education and counsell ing is also very

important. The clinical and psychological

expectations of patients and the clinic team

have to be met.

AcknowledgmentDr DerekJones, a friend and colleague of the author,provided support and advice in reviewing this article.

Audit Commission (2000) Fully Equipped report onprostheilc and orthotic seryices. Audit CommissionPu bl ications, Wetherby

British Standards lnstitution ( 1980) Methods forMeasurement and Recording for Orthopaedic Footweor(BS se43)

Chantelau E, Kushner T, Spraul M ( 1990) Howeffective is cushioned therapeutic footwear inprotecting diabetic feet. Diobetic Medicine 7(4):355-9

Edmonds ME, Foster AVM (2005) Monoging theDiobetic FootZnd edition. Blackwell Science, Oxford

Edmonds ME, Foster AVM, Sanders L (2004) ProdicalMonuol of Diabetic Foot Care. Blackwell Science,Oxford

Janisse DJ ( 1993) A scientif ic approach to insole designfor the diabetic foot. The Foot 3(3): 105-8

Munro WA, Jones Q Stang D Benbow S (2005)Clinical experience of the PRAFO in themanagement of the diabetic foot. Allied HealthProfessions Clinicol Eflbctiveness Meeting, Scotland

Pratt DJ, Tollafield DR (1997) An introduction tomechanical therapeutics. ln: DR Tollafield, LMMerriman, eds. Clinicol Skills in Treoting the FootChurchill Livingstone, London

Rose GK (1986) Orthotics: principles ond procilce.Heinemann Medical Books, London

Schaff PS, Cavanagh PR (1990) Shoes for theinsensitive foot the effect of a "rocker bottom"shoe modification on plantar pressure distribution.Foot ond Ankle I l(3): 129-40

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Tovey Fl, Moss MJ (1984) Manufacturing diabeticfootwear. Core, Science ond Prodice 4(2): l7-2

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