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Correctly assessing diabetic foot ulceration

Lorna Hicks
DPodM
Lead Diabetes Specialist Podiatrist
Conwy and Denbighshire
NHS Trust
Glan Clwyd Hospital
Wales

Diabetic foot ulceration is a significant health problem worldwide. In the UK the estimated annual cost of ulceration, infection, osteomyelitis and amputation associated with diabetic peripheral neuropathy is £251.5 million.(1) Approximately 15% of people with diabetes develop at least one foot ulcer during their lifetime, and 75% of these cases have neuropathy. Up to 35% of the diabetic population have peripheral neuropathy; the majority are asymptomatic.(2) For these reasons neuropathy is the most important risk factor to assess for. The prevalence of peripheral neuropathy in type 2 diabetes is around double that found in type 1.(3)
However, foot ulcer risk and neuropathy are not the same thing; a third of patients may have neuropathy, but only a fifth of these at any one time have had a foot ulcer.(4) There are, however, other factors to consider.
Over the last 15 years there has been a huge increase in the amount of research and investigations into the causes and impact of diabetic neuropathy, and more is now known about what to assess and how the disease process is influenced by health interventions and patient actions. A recent literature review reveals the vast amount of information available to us for assessment and management of the foot in diabetes.(5) The patient's perception of his or her risk appears to be what drives behaviour.(6) Therefore the assessment and education provided for the patient needs to be carefully considered if it is to cause behavioural change that will preserve feet.

Factors to consider
There are a multitude of factors that indicate risk of ulceration. These may be classified as key or contributory factors (see Box 1).

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Essentially the difference is that contributory factors may exist but are unlikely to cause foot ulceration unless one or more of the key factors is present, for example corns and callus - the reason for their inclusion is that it should form part of the primary assessment because its presence is a reason for referral for treatment. Similarly, peripheral vascular disease - if it is present and the foot is otherwise unaffected - does not tend to precipitate ulceration. However, its presence may require further investigation or intervention. This is particularly the case when there are symptoms, and it is strongly linked to the risk of amputation as well as delayed healing, as wounds can occur resulting in chronic ischaemic ulcers.
These factors do not all contribute equally to the risk. How well these are assessed and graded will impact significantly on the success of any assessment, screening and prevention programme. It is vital to assess a person for presence or absence of risk factors, then identify their level of risk and provide education and intervention as appropriate.
Screening and assessment should be a key part of any prevention strategy. Expert observation of feet allows us to spot many of the key indicators of ischaemia or neuropathy. However, when these coexist the signs become confusing and symptoms may be masked.
Tests for peripheral neuropathy and peripheral arterial disease give quantitative results that are the foundation for future assessors and evaluation of the disease process.

Assessment

Neuropathy
Neuropathy is the most important factor to test for because it is involved in the majority of diabetic foot ulcerations, and merely identifying it and providing simple education can reduce the number or severity of ulcerations. There are several valid tools for assessment of this, such as the neuropathy symptom score and the neuropathy disability score.(7) It was observed that symptomatic peripheral neuropathy affects 10% of the diabetic population at any one time and is characterised by typical symptoms (see Box 2).(2) Up to a further 25% are asymptomatic, characterised by numbness and absence of feeling. Typical features of the neuropathic foot include claw toes, prominent metatarsal heads and marked callus formation, which is susceptible to ulceration (see Figure 1). Equipment that may be used for the physical assessment is listed in Table 1.

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[[NIP25_fig1_30]]

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It could be useful to find out what other healthcare staff in your area are doing or to approach your local diabetes service advisory group (LDSAG) for guidance on any existing local protocol. Using a common, repeatable system for assessment allows valuable audit that can improve effectiveness in future.
The monofilament test used alone has a direct correlation with risk of ulceration. Patients who could not feel a monofilament were 10 times more likely to ulcerate over a given period than those who could feel the monofilament.(10) The monofilament does not diagnose neuropathy on its own, but when used properly as a single test it accurately identified a person's risk status for ulceration. Put simply, if the patient can feel it then protective sensation is intact; if the patient cannot feel it then sensation is not good enough to protect their feet from injury. For example, patients may wear shoes that are too tight because they cannot feel the correct size shoe adequately. Sometimes the repetitive stress of walking has worn a hole in their foot under the callus that has not been removed because they could not feel the discomfort it would normally cause.
There are five sites to test on each foot.(2) The monofilament comes with instructions for this. The sites are the pulp of the great toes and one, two, three and five metatarsal heads. The test has failed if the subject feels eight or fewer sites. There has been recent debate about how many and which sites, but general consensus is that a calibrated 10g monofilament is important (see Table 1) as this produces accurate reproducible results. Experience tells us that common risk sites for pressure ulceration are the great toe and metatarsal heads.
Vibration perception threshold studies produced some of the earliest evidence that insensate feet were at increased risk of ulceration. The study showed a 7.7-fold increased risk of ulceration with an inability to feel 25V on a neurothesiometer test,(3) however, this is expensive equipment. A 128Hz tuning fork is simple to use with no replaceable parts and no need to charge up. It may produce satisfactory results.
If the results of your tests show sensory deficit then there is a need for detailed education and advice, which should include recommending the patient inspects their feet and footwear every day, as sensation is not capable of indicating whether there is something wrong.
Education around evidence of sensory deficit should be clear and easy to understand: for example, if it looks like it should be painful, then treat it as if it is painful. Patients should be advised to seek help and rest their foot until they get help.
Advice should be rephrased for the individual's needs. Scare tactics may frighten patients into inertia and not seeking help early enough. However, ambiguity should be avoided.
If sensory neuropathy has been detected then it is wise to refer for podiatry evaluation, particularly if callus is present. Plantar pressure evaluation would be the next step. Insoles, footwear and orthotic therapy need to be considered.

Elevated plantar pressure
Elevated plantar pressure is second only to neuropathy as a contributor to diabetic foot ulceration.(11,12) When combined with neuropathy the effect can be devastating if left undetected and therefore untreated (see Table 2). The study of a semiquantitative plantar pressure device for detection of elevated plantar pressure validated interobserver agreement and sensitivity reached 90% specificity.(13) The product they used was Podotrack, which is called Pressurestat(TM) in the UK. It is simple to use and produces a pressure map of the patient's foot that can form part of the patient's records. It may be folded without distorting the image. The map is in shades of grey, so it is easily photocopied to append to referrals. It has a semicalibrated scale; pressure areas more than 6kg/cm(2) are at high risk for ulcer development.

[[NIP25_table2_32]]

Corns and callus
Corns and callus contribute to elevated foot pressures.(14) Meticulous debridement is imperative to significantly reduce the pressure and thus avoid ulceration.(15) Simple inspection of feet for the presence of callus then referral to the podiatrist for further management will deal adequately with this factor. The podiatrist may prescribe insoles to reduce callus and corn formation and thus further reduce risk.

Foot deformity
Simple foot inspection will enable identification of foot deformity, and referral for footwear, insoles or orthoses may be arranged if required. The presence of foot deformity is a proven risk factor for ulceration.16 Extra-depth footwear is needed to prevent pressure ulcers on the dorsum of deformed insensate toes or to accommodate insoles or orthoses. These are needed to modify pressure distribution and prevent plantar ulcerations.

Peripheral vascular disease
The usual examination for this involves observation and palpation of dorsalis pedis and posterior tibial pulses. Observations should include colour and quality of the skin, soft tissues and nails, noting any atrophy, cyanosis or ischaemic rubor. Presence of hair is usually a good sign, but its absence may be normal for that individual.
Posterior tibial pulse is behind the medial malleolus. Dorsalis pedis pulse is on top of the arch of the foot lateral to the long extensor tendon of the great toe.
Symptoms such as intermittent claudication and rest pain may be masked by the presence of neuropathy.
Ankle brachial pressure index may be falsely elevated if there is arterial calcification.
Capillary refill time (CRT) should be less than four seconds. This is when pressure is applied to cause blanching of the skin. Pinch the toe then release and the time for colour to be restored is recorded as CRT. Prolonged refill times suggest the tissues are not well perfused and injuries would have prolonged healing times. Repair of injured tissues has five times greater demand on the arterial supply than maintenance of intact tissues. It is therefore essential to protect feet with impaired circulation from injuries (see Figure 2). The importance of protection should be conveyed without causing alarm.

[[NIP25_fig2_33]]

Education
Fear of amputation sometimes scares people into not seeking help; it may be seen as putting off the inevitable. However, the risk of ulceration needs to be explained. Any written information provided after assessment should be discussed.
Seeking help early is vital if serious complications are to be avoided. In order to get help early the problem needs to be detected in the first instance, which requires daily inspection of feet and footwear. The patient is more likely to check their footwear if they see their footwear and insoles checked as part of the assessment, and it elevates the importance of this simple task. If the footwear is not examined then important factors could be missed.
As well as written information, which has to be standardised to a degree, discussing and tailoring the information to the patient's needs and lifestyle can make the difference between healthy-living advice that gets ignored and behaviour-changing advice.
One-stop shops for assessing all aspects of diabetes are popular, but we need to be aware of information overload.
There is a need to revise information that is supplied in the same way a student revises for an exam. Pictures are more easily recalled, and illustrated advice is often better remembered.
The International Diabetes Federation recently published a book and data on issues surrounding diabetes and foot complications. There is guidance for patients, carers, clinicians, service providers and policymakers of all professions. There is also useful educational material available from this not-for-profit organisation.

Professional roles and boundaries
The complexity of the diabetic foot, its screening and treatment needs means there is often a blurring of doctor, nurse and podiatrist roles, whether they are specialists in secondary care centres or in a primary care setting. It would be fair to say that some skills are common to most practitioners in the diabetes field, so there is considerable overlap, whereas other skills are definitely within the scope of a particular profession.
Often the major driving forces behind delivery of a high-quality service are local professional interest and what the purchasers wish to pay for.
In some areas the initial screening of sensation and circulation is carried out by the practice nurse during the annual review, then the patient is referred to the podiatry department for further assessments and treatment requirements to be addressed. Further assessments may include some of the sensory testing described in this article if it is not performed in the annual review along with assessment of deformity, footwear, plantar pressures and biomechanics.
In other areas a podiatrist is part of the annual review team in the GP surgery; this allows a slightly different assessment to be done involving pressure analysis and biomechanical evaluation, which tend to be podiatry skills.
Some practice nurses have extended their skill base to cover all aspects of diabetic foot assessment but usually find they work quite closely with a podiatrist to deliver treatment needs.
Often it is the drive of an individual that awakens the latent interest in other professionals. It is useful to find out the extent of local services for onward referral, community services and secondary care services.
This takes some effort but is worthwhile in that it facilitates the formation of a robust network, ensuring that each professional can guide the patient's pathway through the various services. It also makes it easier to seek advice and guidance when more difficult cases are presented.
Ultimately, whichever model is adopted, it is important to ensure all aspects are dealt with but wasteful duplication is avoided.

Conclusion
There is still a great deal to be understood and discovered about diabetic foot problems, such as development of Charcot foot - a condition associated with neuropathy and most commonly seen in diabetes. It usually presents in the acute phase as a hot, red swollen joint, frequently in the foot, with no memorable cause and may look like a severe sprain or septic arthritis. The joint will in time deform and produce chronic pain or discomfort for the sufferer, often with associated ulceration at the load-bearing site of the deformity.
Early detection of neuropathic and/or vascular risk factors is vital in improving morbidity in the diabetic population.
While we cannot prevent all foot ulcerations, a simple quick foot assessment will allow early identification of those risk factors involved.
Time spent in the early stages providing assessment and education gives  patients the opportunity to avoid serious foot complications that may otherwise have threatened life and limb.
Two pivotal studies into complications - the UKPDS (1998)(17) and the DCCT (1993)(18) - demonstrated the impact of well-controlled diabetes, hypertension and cholesterol in reducing the incidence of all complications of diabetes. Furthermore, assessment of these three areas and taking the necessary action forms part of the NICE guidelines for foot care in type 2 diabetes.(19)

References

  1. Gordois A, et al. Diabetic Foot 2003;6(2):62-73.
  2. Young MJ, Matthews C. Diabetic Foot 1998;1(1):22-5.
  3. Young MJ, et al. Diabetologia 1993;36:150-4.
  4. Young MJ. Diabetic Foot 2003;6(2):58.
  5. Boulton AJM. Diabetologia 2004;47:1343-53.
  6. Vileikyte L. Psychological and behavioural issues in diabetic neuropathic foot ulceration. In Boulton AJM, Conner H, Cavanagh PR, editors. The foot in diabetes. 3rd ed. Chichester: Wiley; 2000. p. 121-30.
  7. Abbott CA, et al. Diabetic Med 2002;20:377-84.
  8. Booth J, Young M. Diabetes Care 2000;23(7):984-8.
  9. Young MJ, et al. Diabetes Care 1994;17:557-60.
  10. Rith-Najarian SJ, et al. Diabetes Care 1992;15:1386-9.
  11. Pham H, et al. Diabetes Care 2000;23(5):606-11.
  12. Frykberg R, et al. Diabetes Care 1998;21:1714-9.
  13. van Schie CHM, et al. Diabetic Med 1999;16:154-9.
  14. Murray HJ, Young MJ, Boulton AJM. Diabetic Med 1996;13:979-82.
  15. Petei DL, Foster A, Edmonds M. J Foot Ankle Surg 1999;38(4):251-5.
  16. Lavery L, et al. Arch Inter Med 1998;158:157-62.
  17. United Kingdom Prospective Diabetes Study Group. Lancet  1998;352(9131): 837-53.
  18. Diabetes control and complications trial research group. N Engl J Mrd 1993;329(14): 977-86.
  19. McIntosh A, et al. Prevention and management of foot problems in type 2 diabetes: clinical guidelines and evidence. Sheffield: University of Sheffield; 2003. Available from URL: http://www.rcgp.org.uk/nccpc/docs/guideline.pdf

Resources
International Diabetes
Federation
W:www.idf.org/home

Charcot in Diabetes UK
W:www.charcot.org.uk

World Diabetes Day
14th November 2005
W:www.world diabetesday.org

Edmonds ME, Foster AVM, Sanders L. Practical manual of diabetic foot care. London: Blackwell Publishing; 2004