Orthotic Management of the Diabetic Foot

Diabetic Foot Care

Issues Orthotic Management of the Diabetic Foot Derek Jones Ph.D, M.B.A; William A. Munro, MBAPO Introduction Within the spectrum of challenges presented by diabetes, foot care has rightly become a major area of interest. This article looks at just one aspect of diabetic foot care. Properly prescribed orthotic devices and shoes are critical to diabetic foot care and yet those at the sharp end of providing overall care often poorly understand them.

The number of publications on the diabetic foot has grown dramatically since the 1980’s. However, there is a dearth of evidence for treatments applied to the diabetic foot (1). Evidence that does exist is often based on consensus and rarely comes from large, structured or controlled trials.

In relation to shoes and orthoses this is problem-

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atic and the literature rarely gives specific enough information to allow effectiveness to be determined. Despite this there, is much clinical experience to draw on. International consensus has enabled practical guidelines to be established which can guide multidisciplinary teams wishing to set up a diabetic foot service, no matter where or under whatever conditions they need to work.

It is not what you put on a diabetic foot wound – but what you take off that counts.

Orthotic management is a mechanical challenge as much if not more than a medical one Prescription of orthoses and shoes should be based on the level of risk

This article examines

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why diabetic foot problems are of significance, why orthoses and shoes need to be prescribed with an understanding of the level of risk of a particular individual and offers a framework to determine this risk. It is important that effort is made to protect and preserve the foot from ulceration whilst the patient is at low risk. If breakdown should occur, attention to healing is still economically and socially the right choice and a range of devices are available to assist with healing and ongoing preservation.

Global health issue Diabetes is well understood to be a major and global public health problem that kills 3.8 million people worldwide each year; about the same number of people as HIV and AIDS. In particular, the epidemic of type 2 diabetes is imposing a growing burden on health care systems as the number of people affected around the world is predicted to rise from 151 million in the year 2000 to 300 million by 2025 (2). A great deal of that growth will be in the developing countries of the world that are perhaps not adequately resourced to deal with the challenges that will result.

Since diabetic complications have a great impact on the foot, it is perhaps not surprising that foot problems account for more hospital inpatient days than do any other diabetic problem. Diabetic foot problems can develop extremely quickly, with tissue breakdown occurring rapidly and often complicated by infection (3,4). For this reason it is important to do everything possible to prevent breakdown though good medicine and effective therapeutic footwear that is selected according to the person’s level of risk.

Once ulcers are formed, they are often slow to heal. Orthoses and shoes also have a major role to play in accomplishing and maintaining healing as they deal with the mechanical environment that can contribute to ulceration. To paraphrase Armstrong (5) “It is not what you put on a diabetic foot ulcer – but what you take off.” Even though attention to infection, tissue viability and blood glucose regulation is obviously vital, techniques that assist to reduce the mechanical loads at the foot are critical if breakdown is to be avoided or wound healing is to be accomplished.

In recent years there has been a consensus that the altered wound healing process in diabetes contributes to the development of diabetic foot

ulcers and their delayed healing (6). The normal course of wound healing in people with diabetes appears to be hindered by many factors, including specific metabolic deficiencies and impaired physiological responses (7; 8) Diabetes is therefore an insidious disease and almost every component of the spectrum of hyperglycaemic complications is involved in creating foot lesions. There may be dramatic alterations in all components of the peripheral nerves, the mechanical characteristics of the bones and soft-tissues, altered gait, and changed vascular structure and immune system. All of this together with the compromised process of wound healing, mean that treatments have to deal with both the biological and the mechanical aspects of the problem (9). Long ago, Paul Brand, speaking of the neuropathic foot said, “The whole problem is one of mechanics, not of medicine.

The biological responses to these denervated limbs are qualitatively similar to those of normal limbs. It is the permitted pattern of mechanical stress that is different” Of the broad range of diabetic foot problems, the most important problems clinically are ulceration, amputation and Charcot neuropathy. Foot ulceration is a sign of systemic disease and should never be regarded as trivial (4). Research has shown neuropathy to be the predominant causative factor in the development of foot ulceration (10; 11; 7; 12). In combination with repeated minor trauma, it is the primary cause of diabetic foot ulceration, rather than ischaemia (13).

Since the 1980’s a great deal has been learned about why diabetic feet go wrong and what can be done to prevent and treat problems. In the opinion of some, diabetic foot problems should, of all the complications of diabetes, be the simplest to treat. Despite this, orthoses and shoes are often not well understood by all members of the clinic team.

Why should we care? The consequences of diabetic foot lesions Although foot complications should be simple to treat, the reality is that in addition to causing suffering and morbidity, foot lesions have substantial economic consequences. Of the broad range of diabetic foot problems, the most important clinically are ulceration, amputation and Charcot neuropathy. Bakker (14) reported that worldwide

amputation due to complications of diabetes were estimated at 500,000 per year; representing a rate of one amputation per minute. In a study of the health economics of diabetic foot lesions, Tennvall and Apelqvist (15) report estimates of the total direct cost of a lower-extremity amputation as between $30,000 - $33,500 (in 1998 US dollars) depending on the level, whereas the total direct cost for healing infected foot ulcers not needing amputation as approximately $17,500.

There are therefore clear economic as well as social reasons to aim for prevention and healing.

Orthoses and shoes – the mechanical factors To be effective, orthoses intended for the prevention and treatment of diabetic foot lesions require multi-disciplinary considerations of the prescription process. It is not acceptable to use generic prescription approaches when presented with this complex spectrum of management issues.

The approach one takes should be based on individual risk and clinical need.

Knowing that pressure and shear at the interface between the foot and components of a shoe contribute to breakdown in the neuro-ischemic foot is not enough to know how to design an orthosis or shoe. The overall process is a mechanical challenge in which the external loads applied to the foot are modified and attenuated by the characteristics of a series of interfaces which overlap.

Consider that we actually have interfaces between 1. The ground and outer sole of the shoe 2. The inner sole of the shoe and the foot orthosis 3. The foot orthosis and soft tissue of the plantar surface of the foot 4. The soft tissues of the plantar surface of the foot and bone There is an important message here. Although it is tempting to think that by providing a “tissuelike” material in contact with the plantar surface of the foot, risk of breakdown can be eliminated, this may not always be true. In fact all of the above interfaces and how they work together may need to be considered. The foot orthosis and shoe should be designed “as a unit” and their mechanical characteristics matched so that they work together; recognising the loads that result from ambulation and their effect on the foot and the shoe and orthosis.

Orthoses and shoes can provide • Protection • Prophylaxis • Ambulant pressure relief at areas of risk on the foot In order to determine a prescription for footwear it is important to assess an individuals level of risk.

One simple way to start to think of footwear design criteria is to consider the spectrum of activity that relates to risk. At the lower risk end of the spectrum we might have a newly screened, neuropathic foot, which is non-ulcerated and at the high risk end of the spectrum a deformed neuroischaemic foot that is ulcerated or has had previous breakdowns. Munro (16) set out an approach to the use of orthoses in prophylaxis, treatment and the maintenance of at-risk neuropathic and neuro-ischaemic lesions.

The low-risk foot may indeed be accommodated with “stock footwear or modular footwear. Stock footwear is that which has had no modifications made to its overall size or shape and is made in a material conforming to a catalogue specification.

Modular footwear is that which is modified from catalogue specification but will not be able to accommodate grossly deformed feet or those requiring equinus raises over 15mm. Custom/ bespoke footwear used for the at risk patient will most often be made to a cast of the foot, matched to a last which is modified to accommodate the shape and limitations of the foot. The choice between stock, modular and bespoke shoe should always be based on patient risk rather than fiscal matters. The aim should always be to prevent breakdown and measures to achieve this will always be less expensive in the long term. So how can one decide on the level of risk with an individual?

Prescription matrix for footwear.

A matrix of possibilities can be established to guide the team in their efforts to optimise treatment based on risk. Munro proposed that the matrix could be constructed from the following criteria: 1. Deformity 2. Ambulatory status 3. Biomechanical analysis

4. Neuropathic status 5. Ischemic status 6. Environmental factors It is the nature of this prescription matrix that shapes the function of the shoe and it is the functional requirement of the shoe that defines and constrains the style and design requirements.

Deformity Deformity at the foot and ankle can be classified as Significant or Non Significant.

This definition of significant deformity is related to the balance of the foot between the heel, ball and toe aspects of a normal shoe. If the foot does not line up within these shoe parameters there will be potential friction, shear and pressure implications.

An example of a significant deformity is shown in Figure 1. Rigid Pes Cavus, with an obvious retraction of the toes, creates a situation in which the forefoot from the ball to toe end is not in balance.

Subsequently, when the individual walks, inadequate toe depth within a shoe in the toe off phase of gait will result in an increase in plantar pressure on the metatarsal heads. It may also lead

to dorsal pressure from twisting in the upper material of the shoe.

Non-significant deformity is related to a foot where the balance of heel, ball and toe end does match the balance of the shoe, but where the foot has hammer toes, hallux valgus or other manageable biomechanical anomalies. As described above the presence of a significant deformity will alone rule out the use of stock and modular footwear.

Ambulatory Status

It is important to assess the magnitude and type of ambulatory ability. This may range from an occupationally active level to one of sedentary disabled. The durability and effectiveness of footwear and foot orthoses will be dependant on the punishment meted out to them during activity.

Biomechanical Analysis The extent of deformity is very often linked to the adverse structural biomechanics found at the talo crural, sub talar and midtarsal joints. The concept of what we wish to achieve can be conveyed with an intuitive biomechanical analysis.

It is important to recognise the relationship between the hind foot and forefoot in the three main phases of the gait cycle. The foot complex can be likened to a stable three-peg milking stool in mid stance; where the sub talar joint is neutral and the mid tarsal joint is maximally pronated (Figure 2). Any deviation from this will result in an unstable mechanical foot structure. If the forefoot is hypermobile through an excess of pronation, it is necessary to realign the foot to allow the plantar plane of the forefoot to be parallel with the plantar plane of the hind foot. This can be

achieved orthotically through a process known as posting.

If the forefoot is supinated and rigidity is a factor, orthotic accommodation is required in the form of a cradle. By returning the foot to a stable, mechanical state, pressure redistribution is optimised, thereby reducing pressure and shear.

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. The loss of protective sensation significantly increases the risk of breakdown from friction and shear force between foot and shoe and must be taken into account when formulating a prescription.

Ischemic status The vascular status is also determined at the annual screening, and this too has a bearing on risk of breakdown and tissue viability. Capillary refill time and the status of dorsalis pedis and the posterior tibial pulse are the main clinical indicators here.

Forefoot relief shoes come in varieties with no forefoot plantar protection and those with a follow through sole. The advantage of an exposed forefoot is that there is no plantar pressure on the wound site, however the patient must take care not to damage exposed toes. The design pictured here was created by us to eliminate some of the disadvantages we experienced in practice with these shoes. The design has many of the characteristics of a normal shoe with a through sole and a well-formed heel counter. A carbon fibre keel ensures that the structure does not deform with the twisting loads generated by gait and a custom foot bed can easily be accommodated (Figure 3)

Environment Consideration of the environment covers 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 this would require the hand sewing of the sole to the uppers 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.

Offloading orthoses A wide range of devices are available to assist with the resolution of ulceration. These devices may offload either the forefoot or the hindfoot tissues to relieve or ideally eliminate pressure and shear on the affected area of the foot. Care is needed in the selection and use of the appropriate device. 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 may be used. On too many occasions secondary trauma is initiated by the incorrect use of fracture cast shoes that are rockered in the mid foot and subsequently transfer pressure just where it is not wanted.

The pivot point on the sole is positioned behind the metatarsal heads.

These shoes typically have a rocker to 10 degrees, and our view is that this degree of rocker should form the basis of any device once healing has been achieved. It is also possible to customise a foot orthoses within such a shoe to facilitate optimised pressure redistribution.

Hind foot relief shoes should be used in conjunction with a pressure relieving ankle foot orthoses at the rehabilitation phase of treatment as day time off-loading is nullified if recumbent relief is not also used.

Pressure relieving ankle foot orthoses such as the PRAFO®, (Figure 4) can be used in the prevention and treatment of distal posterior border lesions of the heel and for lesions on the medial and lateral aspects of the 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 is paramount to the safety and efficacy of their use.

In a retrospective study of three major heel wound outcomes it was found that the ability to maintain the foot in a dorsiflexed position with a stable metal upright that resisted plantar flexion was a major benefit to healing, in addition to the wound site being totally pressure relieved. (17) Some patience is certainly needed in diabetic foot care and the wound shown in Figure 5 took 18 months to reach the point shown in Figure 6.

Devices that are preformed contoured polypropylene are useful only in recumbent situations and great care should be taken to monitor deterioration of the plastic which can result in plantar flexion of the foot with resultant increases in forefoot plantar pressure.

The use of Aircast® boots is now widespread and not

without some controversy. We believe it is an extremely useful device if customised to the individual patient and it can satisfy the need for immediate immobilisation of an early stage Charcot.

The ability to use the air cells for graduated compression allows oedema control to take place safely with little chance of damage to tissue viability. The use of a customised foot bed further enhances the plantar pressure relief role. However, it must be stressed that a high degree of patient educational input is the key to successful safe use and in the early stages of use frequent follow up and counselling is desirable.

Bespoke plastic or carbon fibre devices can also achieve axial offloading; these may also be described as CRO or Charcot restraining orthoses. (Figures 7 and 8) The design and fit is individual to the needs of the patient, although these devices should always have a full footplate and be suitably lined and padded to protect tissue viability.

Conclusion

There are strong economic and social reasons to preserve the diabetic foot. Whilst good medical management is essential, the problem of preservation of the foot is actually a mechanical challenge to reduce or eliminate pressure or shear at the interfaces between shoe/orthosis and the foot. There is good consensus about what determines the level of risk with an individual patient and this risk determination should always be the starting point for an orthotic management strategy. This risk determines the choice between stock, modular and bespoke shoes as well as the specification of these. In the event of tissue breakdown, whilst much attention must be given to dressings, antibiotics and other medical matters it is mechanical offloading that will constitute the foundation for healing.

References (1) Edmunds, ME; Foster, AVM; Sanders, LJ (2004) “A practical manual of diabetic footcare” Blackwell Pulishing, 2004. ISBN 1-4051-0715-4 (2) Zimmet, P; Alberti, KCGM; Shaw J “Global and societal implications of the diabetes epidemic” Nature 2001; 414:782-7 (3) Edmonds ME, Blundell MP, Morris HE et al (1986) “The diabetic foot: impact of a foot clinic. “ The Quarterly Journal of Medicine 232: 763-71 (4) Edmunds, ME; Foster, AVM (2006) “ABC of Wound healing: Diabetic foot ulcers” BMJ 2006;332;407-410 (5) Armstrong, DG; Lavery, LA; Nixon, BP; Boulton, AJM (2004) “It’s not what you put on, but what you take off: techniques for debriding and off-loading the diabetic foot wound” Clinical Infectious Diseases, Vol 39, p S92-S99 (6) Veves A, Falanga V, Armstrong DG, Sabolinski ML (2000) Graftskin, a human equivalent, is effective in the management of neuropathic diabetic foot ulcers.

Diabetes Care 24(2): 290-5 (7) Boulton AMJ (1998) “Lowering the risk of neuropathy, foot ulcers and amputation.”

Diabetic Medicine 15 (Suppl 4): S57-9

(8) Pecoraro RE, Ahroni JH, Boyko EJ et al (1991) Chronology and extremities of tissue repair in diabetic lower-extremity ulcers. Diabetes 40: 1305-13 (9) Guyton, GP; Saltzman, CL (2006) “The diabetic foot: Basic mechanisms of disease” J. Bone Joint Surg. Am. 83: 1083-1096, 2006 (10) Walters DP, Gatling W, Mullee MA et al (1992) The distribution and severity of diabetic foot disease: a community study with comparison to a non-diabetic group.

Diabetic Medicine 9(4): 354-8 (11) Levin ME (1995) “Preventing amputation in the diabetic patient.”

Diabetes Care 18:1383-94 (12) De P, Kunze G, Gibby OM, Harding K (2001) “Outcome of diabetic foot ulcers in a specialist foot clinic.”

The Diabetic Foot 4(3): 131-6 (13) Pecoraro PE, Reiber GE, Burgess EM (1990) Pathways to diabetic limb amputation: basis for prevention.

Diabetes Care 13: 516-21 (14) Bakker, K (2004) “The importance of the multidisciplinary diabetic foot team” O Pe Diabetico Conference Porto, Portugal, 4-5th November 2004 (15) Tennvall, GR; Apelqvist, J (2004) “Health-economic consequences of diabetic foot lesions” Clinical Infectious Diseases 2004:39: S132-9 (Suppl 2) (16) Munro, WAM (2005) “Orthotic prescription process for the diabetic foot” The Diabetic Foot, Vol 8, No 2, Summer 2005 (17) Munro, WAM; Jones D “Clinical experience of neuropathic and neuroischemic feet” First Prize for a Poster Presentation. Annual Clinical Effectiveness and Practice Development Conference for AHP’s, Polmont, Scotland, March 2005

Take Away Points

Figures

Author Biography Derek Jones, PhD., MBA is a Bioengineer and Director of Anatomical Concepts (UK) Ltd, and an Associate Professor at the University of Strathclyde in Glasgow, Scotland William Munro MBAPO is an Orthotist, a Director of Anatomical Concepts (UK) Ltd, and a Clinical Associate at the University of Strathclyde in Glasgow, Scotland

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1) A foot with significant deformity – rigid pes cavus 2) A representation of the foot as a three-leg stool 3) A new design of forefoot relief shoe 4) A PRAFO® 5) Severe wound at the calcaneal area 6) Wound in Figure 5 after 18 months pressure relief, debridement and antibiotic management 7) Deformity following Charcot episode 8) A custom Charcot restraining orthosis

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