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A user’s guide to foot screening. Part 2: Peripheral arterial disease

Duncan Fowler, Singhan Murali-Krishnan, Neil Baker

This article is the second of a series of three that aims to provide a clear, simple and practical approach to diabetic foot assessment. Each of the three articles will focus upon a particular aspect of foot examination and, although they will appear individually, they should be combined to give an overall approach to foot examinations. This article focuses upon identifying the at-risk foot due to peripheral arterial disease. The intention is to provide a simple guide to foot examination for everyday use by clinicians that is derived from evidence-based literature.

Peripheral arterial disease (PAD) can be defined as lower extremity atherosclerosis (see Appendix 1 for a definition), which is more common in people with type 2 diabetes, as are other cardiovascular disease pathologies (for example ischaemic heart disease, myocardial infarction and cerebrovascular disease), compared with those without diabetes (MacGregor et al, 1999; Murabito et al, 1997). PAD occurs 20 times more often in people with diabetes compared with the general population (Shaw and Boulton, 2001). It has been reported  that PAD is the single most likely cause of lower extremity amputations in people with diabetes (Pecoraro et al, 1990; Apelqvist et al, 1992; Bird et al, 1999); and, importantly, it is more rapid in its progression and occurs at a younger age compared with cases of such amputations in people without diabetes (Brand et al, 1989; Strandness et al, 1964).

Pure ischaemia in patients with diabetes is not common; however, the presence of reduced arterial supply in combination with neuropathy (neuro-ischaemia) is common, affecting up to 45% of patients with foot ulceration (Shaw and Boulton, 2001; Thomson et al, 1991). With an ageing population and a rising prevalence of type 2 diabetes, an increase in the incidence of neuro-ischaemic ulcers may be anticipated.

Arterial assessment
Arterial occlusive lesions causing ischaemia vary from aortoiliac disease to multi-segmental diffuse lesions extending to the ankle and foot (Hamy and Allen, 2001). Arterial insufficiency is not always easily recognisable until it is quite advanced.

Arterial assessment should be grounded in a clear knowledge of anatomy and pathophysiology, together with the ability to take a comprehensive patient history. Some basic points to remember when taking a patient history in order to assess the diabetic foot are as follows.

Always explain what you are going to do to a patient and why. The time spent examining the foot is a golden opportunity to discuss health education and explore a patient’s beliefs, understanding and fears relating to diabetes and blood flow.

  • Always inform the patient of your findings and what these mean in terms that they can relate to.
  • Reduced arterial blood flow results in poor oxygenation, malnutrition and poor healing capacity of the skin.
  • Screening for contributing factors, particularly smoking, hyperlipidaemia, hypertension and hyperglycaemia, is essential.
  • It is unwise to suggest a diagnosis of PAD based upon one clinical test or observation, such as an absent foot pulse, or cold skin.

In order to undertake a thorough vascular assessment it is essential to have a clear working knowledge and understanding of basic arterial anatomy. Figure 1a illustrates the major arteries of the lower limb, from the division of the aorta into the left and right common iliac arteries to the smaller arteries at the lowest extremity of the foot.

Rationale for vascular assessment of the foot

Why should we regularly test for the presence of arterial disease in people with diabetes? Identification of ischaemia allows intervention strategies to be implemented. These should include appropriate podiatry provision, especially good nail and skin care; targeted education; and, more holistically, a full and prompt review of cardiovascular protection measures such as management of hypertension, hyperlipidaemia, glycaemic control and antiplatelet therapy.

Additionally, if vascular assessment is performed annually in a standardised way, any deterioration in the patient’s circulation can be promptly identified.

History taking
Comprehensive history taking is vital to assess the vascular status and general fitness of the patient. General vascular history includes asking about previous heart attacks and angina, other diabetes-related complications (for example, eye disease, renal disease and neuropathy), current medication, and general fitness including exercise tolerance. his is important because many older people with arterial disease have serious co-existing conditions which may influence future decisions about treatment.

Presence of other concomitant risk factors for PAD such as the use of tobacco, excessive alcohol  consumption and hyperlipidaemia should be elucidated.

More specifically, history to determine intermittent claudication and/or rest pain should be ascertained as it is important to distinguish this from other pain aetiologies like neuropathy, plantar fascitis, meralgia and Morton’s metatarsalgia (Table 1).

Clinical manifestations of PAD
Remember, if the skin looks healthy, then it probably is! When examining feet it is good practice not to be drawn to the most obvious clinical feature, taking time to systematically examine the lower leg and the whole foot making note of any features that may be observed. Only when all of the presenting features are put together should an opinion be reached regarding the status of the patient’s arterial blood supply. The most commonly occurring clinical features of reduced arterial supply are discussed below (see also Table 2).

Nail dystrophies
The toenails are generally of poor quality and are either very thin or yellowed and thick. They may be hard to cut or quite brittle and characteristically they are very slow growing. It is not uncommon for ulcers to occur under the nail plate, especially when the nails are thick.

Skin condition
Characteristically the skin condition is very poor with a general loss of substance. This is clearly demonstrated by gently pressing the skin at the end of a toe; in a healthy state the skin will spring back, but, in patients with ischaemia the skin remains depressed. It can be likened to ‘a grape that has been in the fruit bowl too long!’ The skin may be very dry with hair loss and, not uncommonly, multiple small skin fissures or increased skin creases are observed, particularly in the arch and around the heels.

Callused/hard skin
If one or more calluses are present, they are often very thin and hard, occurring in small isolated areas unlike the diffuse thick calluses seen in patients with neuropathy. Calluses in patients with ischaemia may be described as appearing like ‘onion skins’.

Skin colour
The colour of the skin is determined by the amount and condition of the blood flowing through it; therefore it may vary in colour significantly. Generally the skin is more pallid than normal but can range from intense deep pink to dusky red to mauve/purple.

Skin temperature
The skin temperature is determined by the amount of blood flowing through it and, therefore, may vary. This is particularly true during cold or wet weather. Localised areas of increased skin temperature should alert the examiner to the possibility of disease processes such as infection or gout.

Toes
The toes of patients with significant arterial disease are often slightly swollen and dark pink in colour, resembling ‘beef chipolata sausages’. However, if an individual toe has this appearance and ulceration is present, osteomyelitis should be suspected.

Ulceration and gangrene
Ulceration due to pure ischaemia is nearly always located on the dorsum of the foot and is rare. It is characteristically painful and can deteriorate very rapidly, exposing tendons and bone. The surrounding tissue is very devitalised and the wound base has no substance.

The vast majority of ulcers can be described as ‘neuro-ischaemic’ and, as their name suggests, have both neurological and arterial components. Characteristically they occur on the margins of the feet, especially around the heels, resulting from skin fissures, or at the sides of the first and fifth metatarsal heads. They can also occur over the dorsal toe joints or tips (Figure 2).

The ulcers tend to have a ‘punched out’ appearance with thin ‘glassy’ surrounding callus. The ulcer bases are very frequently sloughy with interspersed light granulation tissue. Characteristically these lesions are very slow to heal and are prone to frequent low-grade infections.

Gangrene is the result of either insufficient blood flow to sustain any life (leading to mummification of tissue, most commonly seen in the digits [Figure 3]) or infection, or a combination of both. In the presence of infection, gangrene can spread to neighbouring toes or through larger areas of the foot.

Vascular assessment
It is recommended that in patients with diabetes an annual inspection of vascular status should involve:

  • identification of symptoms related to ischaemia
  • examining the foot for clinical manifestations of ischaemia
  • palpation of foot pulses in both feet.

Additional tests that may be required include:

  • palpation of popliteal and femoral pulses if foot pulses are reduced or absent
  • using hand-held Doppler to locate non-palpated pulses
  • ankle systolic pressures/ankle brachial pressure indices (ABPIs)
  • Buerger’s test – elevation and dependency
  • toe pressures
  • transcutaneous oximetry.

Where possible, one must try to ensure that patients are put at ease, examined in a warm room, and an explanation of what is being done and why given.

It must be remembered that small arteries are very vaso-active and will, therefore, constrict easily and so may affect some assessment tests, especially Doppler signals.

Clinical examination: Pulse
A pulse is a reflection of the pressure wave generated by ventricular contraction and relaxation during the cardiac cycle and is a means of clinically determining arterial inflow to the lower extremity. Heart rhythm and output, ambient temperature and degree of arterial stenosis or occlusion are factors that influence the amplitude of a palpated pulse (Baker and Rayman, 1999).

It is a common misunderstanding that a palpable pulse equates to good perfusion (Andros et al, 1988). Markers such as intermittent claudication and rest pain may be dulled or confused with other causes such as painful neuropathy or spinal stenosis.

Feeling for the pulses
Place your first and second fingers lightly on the patient’s skin overlying the pulse site you are examining. You should feel a regular light beating under the pulps of your fingers. If you cannot feel a pulse, move your fingers slightly to the adjacent skin until you can locate one. If you still cannot feel a pulse try the next site and then return to this one afterwards and try again. Reasons for difficulty in obtaining a pulse can include:

  • oedema
  • poor technique
  • abnormal position of arteries
  • diseased or absent arteries
  • low cardiac output.

In most instances it is sufficient to record pulses as being present or absent, but they can also be further clarified as weak or strong and regular or irregular.

Palpation of dorsalis pedis
The dorsalis pedis pulse is located on the dorsum of the foot running along the lateral side of the first metatarsal shaft at approximately the mid-point (Figure 1b). This artery is congenitally absent in approximately 10% of the population and may also deviate slightly more laterally than stated above.

Palpation of posterior tibial pulses
The posterior tibial pulse is considered to be more anatomically constant and is usually located just behind the medial malleolus at the level of the ankle joint (Figure 1c).

When the foot pulses cannot be palpated, a hand-held Doppler can be used to detect the arteries. Additionally, it is important that if the pedal pulses cannot be palpated, an examination of the popliteal and the femoral arteries should be performed to delineate the level of stenosing disease.

Popliteal pulse palpation
The popliteal artery is located behind the knee in the popliteal fossa and is located just lateral to the midline of the knee. This pulse is not an easy one to palpate and requires considerable practice. The patient should be either seated with legs extended or lying down, with the knee bent to approximateley 60º and the foot flat on the couch. Hands should be placed either side of the knee so that the fingers meet in the middle at the back of the popliteal fossa with the thumbs gently pressing either side of the kneecap at the front of the knee. In this position the examiner’s fingers should be able to feel a pulse, although the fingers may have to be moved slightly sideways. If the popliteal is very easy to palpate and seems wider than a normal pulse it is possible that you are palpating a popliteal aneurysm.

Femoral pulse palpation
As the femoral artery is felt in the groin it is essential that a chaperone is present when palpating it. The artery is located midway along the groin crease and is usually quite easy to feel. The patient should be lying as flat as possible with the legs extended when feeling for this artery. You will also have to press reasonably firmly if the patient is not thin.

Doppler examinations
The use of a hand-held doppler to examine lower limb pulses and particularly to obtain systolic ankle pressures is becoming more commonplace. Doppler signals can be very useful for locating non-palpable arteries, patient education and quantifying disease progression, especially when waveform analysis is performed. Additionally, they can prove a useful surveillance tool following vascular surgery or angioplasty. Many resources have been produced on the use and interpretation of hand-held Dopplers such as ‘Dopplers and the diabetic foot’ (Vowden et al, 1999) and ‘Examination of the diabetic foot’ (video; Huntleigh Diagnostics, Cardiff).

However, in brief, a normal Doppler arterial signal should be multi-phasic with three distinct audible components (triphasic signal) relating to forward flow in peak systole followed by reverse flow in diastole and lastly forward diastolic flow. A two-component signal (biphasic), generally loss of reverse flow, is also considered to be a ‘normal’ arterial signal, but a degree of arterial obstruction may be present. A single component signal (monophasic), forward flow only, signifies a moderate to severe degree of ischaemia. As a general rule if the signal is of low pitch and muffled, significant arterial disease is likely to be present.

Ankle pressures
Using a hand-held Doppler (Figure 4) and a sphygmomanometer an ankle systolic pressure measurement can be obtained. This is achieved by placing a standard arm sphygmomanometer cuff around the ankle, which is inflated after a pedal pulse is identified with a Doppler probe. The cuff is inflated to occlude the arterial signal and then slowly deflated. The point at which the arterial signal can be heard again is the systolic pressure. This is then repeated at the other pedal pulse sites. The brachial systolic pressure is then obtained and divided into each of the pedal pulse values. The figure obtained for each site is the ABPI (Table 3).

Pressure in the toes can also be measured and is considered to be more reliable as they are less affected by arterial calcification. However, this is not easy to perform in a normal clinical setting.

It is, however, important to stress that, although ankle pressures are very useful, they should be used in conjunction with a good clinical examination, especially for referral criteria and as a means of determining likely outcomes of healing (Apelqvist et al, 1989).

Beurger’s test: Elevation and dependency
Beurgers test is a very useful clinical method to determine whether there is significant arterial disease, especially if arterial calcification is strongly suspected when calculating an ABPI. The principle of this test is that there should be sufficient pressure within the arterial tree to maintain adequate blood flow through the limb when elevated to an angle of 30º from the horizontal or 30cm above the level of the heart. A positive result, signifying arterial disease, is observed when the elevated limb becomes pale and a dusky ‘sunset’ red when placed in a dependent position. The elevation test can be supplemented by listening to the Doppler signal while elevating the limb. If the signal fades or disappears, some arterial obstruction is present and the lower the raised limb is when this occurs the more significant the disease; this is called the ‘pole’ test (Smith et al, 1994).

Buerger’s test method is as follows.

  • The patient is laid as flat as possible.
  • The leg is supported and lifted by the examiner either to a height of 30cm above the heart or to an angle of 30º from the horizontal (slightly higher if the patient is not laying flat) and held for 2–3 minutes.
  • The colour of the leg is observed. If the limb or foot becomes pale there is a reduced arterial pressure and thus restricted flow.
  • The limb is then lowered over the side of the couch into a dependent position and observed for colour changes. If a deep red colour is observed in the toes which then spreads proximally, significant arterial disease is likely to be present.
  • The time taken for these changes to occur signifies the severity of the disease.

Pathways of care
For suggested pathways of care following lower limb assessment see Table 4.

Once PAD has been diagnosed, patients need to be given clear and relevant advice. Below is some patient’s advice that may be useful.

  • Avoid extreme cold; keep legs and ankles warm in the winter by wearing thermal hosiery or long johns.
  • Apply emollients at least once daily, massaging well into the skin (not between the toes).
  • Avoid slip-on shoes and slippers no matter how soft the uppers may be.
  • File any rough edges on toenails and cut them carefully to follow the shape of the end of the toe, if they are not being cut professionally.
  • If any cracks to live tissue, oozing around/under nails or between toes are observed seek advice.
  • Try to take exercise daily as long as pressure relief is accounted for.

Conclusion
This simple approach to screening for PAD in people with diabetes relies upon good history taking, careful foot observation and clinical examination. It is intended that this article will act as a basis to develop further understanding, skills and expertise to identify PAD as early as possible and help prevent some of its devastating potential consequences in diabetic foot disease.

REFERENCES:

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Apelqvist J, Castenfors J, Larsson J, Stenstrom A, Agardh CD (1989) Prognostic value of systolic ankle and toe blood pressure levels in outcome of diabetic foot ulcer. Diabetes Care 12(6): 373–8
Apelqvist J, Larsson J, Agardh CD (1992) Medical risk factors in diabetic patients with foot ulcers and severe peripheral vascular disease and their influence on outcome. Journal of Diabetes and its Complications 6(3): 167–74
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Pecoraro RE, Reiber GE, Burgess EM (1990) Pathways to diabetic limb amputation. Basis for prevention. Diabetes Care 13(5): 513–21
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Smith FC, Shearman CP, Simms MH, Gwynn BR (1994) Falsely elevated ankle pressures in severe leg ischaemia: the pole test – an alternative approach. European Journal of Vascular Surgery 8(4): 408–12
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