Assessment of Diabetic Foot

In most patients, peripheral neuropathy and peripheral arterial disease (PAD) (or both) play a central role and Diabetic Foot Ulcers are therefore commonly classified as :

  • Neuropathic
  • Ischaemic
  • Neuroischaemic

PERIPHERAL NEUROPATHY

Peripheral neuropathy may predispose the foot to ulceration through its effects on the sensory, motor and autonomic nerves:

  • The loss of protective sensation experienced by patients with sensory neuropathy renders them vulnerable to physical, chemical and thermal trauma
  • Motor neuropathy can cause foot deformities (such as hammer toes and claw foot), which may result in abnormal pressures over bony prominences
  • Autonomic neuropathy is typically associated with dry skin, which can result in fissures, cracking and callus. Another feature is bounding pulses, which is often misinterpreted as indicating a good circulation

PERIPHERAL ARTERIAL DISEASE

People with diabetes are twice as likely to have PAD as those without diabetes. It is also a key risk factor for lower extremity amputation. The proportion of patients with an ischaemic component to their DFU is increasing and it is reported to be a contributory factor in the development of DFUs in up to 50% of patients. It is important to remember that even in the absence of a poor arterial supply, microngiopathy (small vessel dysfunction) contributes to poor ulcer healing in neuroischaemic DFUs. Decreased perfusion in the diabetic foot is a complex scenario and is characterised by various factors relating to microvascular dysfunction in addition to PAD. DFUs usually result from two or more risk factors occurring together. Intrinsic elements such as neuropathy, PAD and foot deformity (resulting, for example, from neuropathic structural changes), accompanied by an external trauma such as poorly fitting foot-wear or an injury to the foot can, over time, lead to a DFU.

 

 

Feature Neuropathic Ischaemic Neuroischaemic
Sensation

 

Sensory loss

 

Painful

 

Degree of sensory

loss

Callus/necrosis

 

Callus present and

often thick

 

Necrosis common

 

Minimal callus

Prone to necrosis

Wound bed

 

Pink and granulating, surrounded by

callus

 

Pale and sloughy

with poor

granulation

 

Poor granulation
Foot temperature

and pulses

 

Warm with bounding pulses

 

Cool with absent

pulses

 

Cool with absent

pulses

Other

 

Dry skin and

fissuring

 

Delayed healing

 

High risk of

infection

Typical location

 

Weight-bearing

areas of the foot,

such as metatarsal

heads, the heel and

over the dorsum of

clawed toes

 

Tips of toes, nail

edges and between

the toes and lateral

borders of the foot

 

Margins of the

foot and toes

Prevalence

 

35% 15% 50%

 

By applying the staging process to all diabetic foot patients it is possible, through one simple assessment, to detect the conditions that need addressing and plan their treatment using simple but fundamental principles.

 

  1. Practical assessment, which consists of history-taking, examination and investigations.

 

  1. Classification of the diabetic foot into the neuropathic, ischemic and neuroischaemic foot.

 

  1. Staging the foot. The six specific stages in the natural history of the diabetic foot.

 

Stage l Normal foot

Stage 2 High-risk foot

Stage 3 Ulcerated foot

Stage 4 Infected foot

Stage 5 Necrotic foot

Stage 6 Unsalvageable foot

 

PRACTICAL ASSESSMENT

This can be divided into three parts:

  • History-taking
  • Examination
  • Investigations

History

The history can be divided into the following sections:

  • Presenting complaint: Skin breakdown, Oedema, Colour change, Pain, discomfort and abnormal, Ulcer sensations.
  • Past foot history: Previous ulcers and treatment, Amputations:Major,Minor, Peripheral angioplasties,Peripheral arterial bypasses.
  • Diabetic history: Type, Duration, Treatment.
  • Past medical history: Trauma, previous hospital admissions, surgeries, Associated co mordidities.
  • Drug history: History of allergy, current medications NSAIDS.
  • Family history:
  • Psychosocial history: Occupation, Number of cigarettes smoked per day, Number of units of alcohol per day, Psychiatric illness; drug or alcohol dependency, etc. Home circumstances: Type of accommodation.

 

The examination should be performed systematically.

It consists of five parts:

  • Inspection
  • Palpation
  • Neurological assessment
  • Footwear assessment
  • General examination.

 

Inspection

The feet should be fully examined in a systematic fashion: first the right and then the left, including dorsum, sole, medial border, lateral border, back of the heel, malleoli and interdigital areas, with a full assessment of the following:

  • Skin:
  • Corns and callus
  • Nails
  • Oedema
  • Deformity
  • Limited joint mobility
  • Colour
  • Necrosis.

Inlow’S

60-second Diabetic Foot Screen Screening Tool

Question/Test SCORE
  Rt Lt
1. Skin

0 =  intact and healthy

1 =  dry with fungus or light callus

2 =  heavy callus build up

3 =  open ulceration or history of previous ulcer

   
2. Nails

0 =  well-kept

1 =  unkempt and ragged

2 =  thick, damaged, or infected

   
3. Deformity

0 =  no deformity

2 =  mild deformity

4 =  major deformity

   
4. Footwear

0 =  appropriate

1 =  inappropriate

2 =  causing trauma

   
5. Temperature – Cold

0 =  foot warm

1 =  foot is cold

   
6. Temperature – Hot

0 =  foot is warm

1 =  foot is hot

   
7. Range of Motion

0 =  full range to hallux

1 =  hallux limitus

2 =  hallux rigidus

3 =  hallux amputation

   
8. Sensation – Monoflament Testing

0 =  10 sites detected

2 =  7 to 9 sites detected

4 =  0 to 6 sites detected

   
9. Sensation – Ask 4 Questions:

i.    Are your feet ever numb?

ii.   Do they ever tingle?

iii. Do they ever burn?

iv.   Do they ever feel like insects are crawling on them?

0 =  no to all questions

2 =  yes to any of the questions

   
10. Pedal Pulses

0 =  present

1 =  absent

   
11. Dependent Rubor

0 =  no

1 =  yes

   
12. Erythema

0 =  no

1 =  yes

   
 Total Score  

Screening for foot ulcers and/or limb-threatening complications. Use the highest score from left or right foot.

Score = 0 to 6 → Recommend screening yearly

Score = 7 to 12 → Recommend screening every 6 months

Score = 13 to 19 → Recommend screening every 3 months

Score = 20 to 25 → Recommend screening every 1 to 3 months.

 

 

Palpation

Palpation should take place to assess:

  • Pulses
  • Temperature of the foot
  • Oedema
  • Crepitus.

Pulses

The most important manoeuvre to detect ischaemia is the palpation of foot pulses, an examination which is often undervalued.

  • The dorsalis pedis pulse is palpated, using the index, middle and ring fingertips together, lateral to the extensor hallucis longus tendon on the dorsum of the foot
  • The posterior tibial pulse is palpated below and behind the medial malleolus

If either of these foot pulses can be felt then it is highly unlikely that there is significant ischaemia in the foot. If both pulses are absent, the patient should undergo Doppler examination to measure the ankle brachial pressure index and to record the blood velocity profile or sonogram.

Temperature of the foot

Skin temperature is compared between both feet with the back of the examining hand. Normally any one area on a foot will be within 2°C of the corresponding area on the other foot. Warm areas or hot spots outside this range indicate inflammation which may be due to infection, fracture, Charcot’s osteoarthropathy or soft tissue trauma. An increase in unilateral pedal temperature, especially in the absence of ulceration, is best presumed to be Charcot’s osteoarthropathy.

Causes of the hot foot

  • Soft tissue injury or fracture
  • Cellulitis
  • Charcot foot
  • Gout
  • Deep vein thrombosis.

Causes of the cold foot

  • Chronic ischaemia
  • Acute ischaemia
  • Cardiac failure.

 

TESTING FOR LOSS OF SENSATION

Two simple and effective tests for peripheral neuropathy are commonly used:

  • 10g (Semmes-Weinstein) monofilament
  • Standard 128Hz tuning fork.

The 10g monofilament is the most frequently used screening tool to determine the presence of neuropathy in patients with diabetes.  It should be applied at various sites along the plantar aspect of the foot. Guidelines vary in the number of sites advocated, but the international consensus is to test at three sites. A positive result is the inability to feel the monofilament when it is pressed against the foot with enough force to bend it.

Neuropathy is also demonstrated by an inability to sense vibration from a standard tuning fork. Other tests are available, such as the biothesiometer and neurothesiometer, which are more complex handheld devices for assessing the perception of vibration.

The International Working Group on the Diabetic Foot (IWGDF) recommends the following procedure for carrying out the  monofilament test.

  • The sensory examination should be carried out in a quiet and relaxed setting
  • The patient should close their eyes so as not to see whether or where the examiner applies the monofilament
  • The patient should sit supine with both feet level
  • First apply the monofilament on the patient’s hands or on the inside of the arm so they know what to expect
  • Apply the monofilament perpendicular to the skin surface with sufficient force to bend or buckle the monofilament
  • Ask the patient:

— Whether they feel the pressure applied (yes/no)

— Where they feel the pressure (left foot/right foot)

  • Apply the monofilament along the perimeter of (not on) the ulcer site
  • Do not allow the monofilament to slide across the skin or make repetitive contact at the test site
  • The total duration of the approach (skin contact and removal of the monofilament) should be around 2 seconds
  • Apply the monofilament to each site three times, including at least one additional ‘mock’ application in which no filament is applied
  • Encourage the patient during testing by giving positive feedback

— Protective sensation is present at each site if the patient correctly answers two

out of three applications

— Protective sensation is absent with two out of three incorrect answers

 

 

Footwear assessment

It is important to examine both shoes and socks.

Examination of patient’s footwear

  • Is the shoe long enough?
  • Is the toe box broad and deep enough?
  • Are the heels low (below 5 cm)?
  • Does the shoe fasten with a lace or strap to prevent friction? Slip-ons are unsuitable for everyday wear.
  • Is the sole thick enough to provide protection from puncture wounds?
  • Is the shoe lining worn, with rough areas that may prove irritating and warrant replacement?
  • Are there foreign bodies within the shoes?
  • Is there excessive wear under hallux suggesting a hallux rigidus?
  • Is there wear across the whole of the tread suggesting pes cavus?
  • Does the shoe avoid pressure points over the toes or margins of the feet?
  • Does the heel cup fit snugly round the heel?
  • What other types of shoes does the patient wear and when? Patients should be advised not to wear slippers around the house.

Examination of patient’s socks

  • Are the socks large enough?
  • Are the seams too prominent?
  • Is there a tight band at the top?
  • Are the socks in good repairano holes or lumpy darns?
  • Are the socks made of absorbent material?
  • Are the socks very thick, taking up too much space in the shoe?

 

General examination

As part of the diabetic foot assessment, and indeed the

diabetic assessment, all patients should have a physical

examination including the following systems:

  • Cardiovascular
  • Respiratory
  • Abdomen
  • Eyes: Visual acuity Fundi.

Investigations

Investigations include:

  • Neurological
  • Vascular
  • Skin temperature
  • Laboratory
  • Radiological
  • Foot pressures.

 

Vascular

A small hand-held Doppler can be used to quantify the vascular status. Used together with a sphygmomanometer, the brachial systolic pressure and ankle systolic pressure can be measured, and the pressure index, which is the ratio of ankle systolic pressure to brachial systolic pressure, can be calculated. In normal subjects, the pressure index is usually > 1, but in the presence of ischaemia is < 1. Thus, absent pulses and a pressure index of <  1 confirms ischaemia. Conversely, the presence of pulses and a pressure index of > 1 rules out ischaemia; this has important implications for management, namely that macrovascular disease is not an important factor and further vascular investigations are not necessary.

Skin temperature

It is helpful to follow-up the clinical assessment of skin temperature with the use of a digital skin thermometer. An infrared thermometer is ideal and skin temperatures are compared between similar areas on each foot. This is particularly helpful in the management of the Charcot foot.

Laboratory

Laboratory investigations are determined by clinical findings, but the following investigations are useful as a baseline in most patients:

  • Full blood count (to detect anaemia or polycythaemia),and white blood cell count (to reflect the presence of infection)
  • Serum electrolytes, urea and creatinine (to assess baseline renal function
  • Serum bilirubin, alkaline phosphatase, gamma glutamyl transferase, aspartate transaminase (to assess baseline liver function
  • Blood glucose and HbA1c (to assess diabetic control
  • Serum cholesterol and triglycerides (to assess arterial disease risk factors
  • C-reactive protein (as an acute inflammatory marker).

Radiological

These will be determined by the clinical presentation, and may not always be necessary. However, in most cases, an X-ray of the foot will be required to detect:

  • Osteomyelitis
  • Fracture/dislocation
  • Charcot foot
  • Gas in soft tissues
  • Foreign body.

CLASSIFICATION AND STAGING

After completing this basic assessment, it will now be possible to classify the diabetic foot and distinguish between the neuropathic foot and the neuroischaemic foot, as for practical purposes, the diabetic foot can be divided into these two distinct entities.

Neuropathic foot

  • The neuropathic foot is a warm, well-perfused foot with bounding pulses and distended dorsal veins due toarteriovenous shunting
  • Sweating is diminished so skin and any callus tend to be hard and dry and prone to fissuring
  • Toes are clawed and the arch of the foot may be raised
  • Ulceration commonly develops on the sole of the foot,associated with neglected callus and high plantar pressures
  • Despite the good circulation, necrosis can develop secondary to severe infection
  • The neuropathic foot is also prone to bone and joint problems which we refer to as Charcot’s osteoarthropathy

Neuroischaemic foot

  • The neuroischaemic foot is a cool, pulseless foot with poor perfusion and almost invariably also has neuropathy.
  • The colour of the severely ischaemic foot can be a deceptively healthy pink or red caused by dilatation of capillaries in an attempt to improve perfusion
  • The neuroischaemic foot may be complicated by oedema, often secondary to cardiac failure or renal impairment
  • Ischaemic ulcers are commonly seen around the edges of the foot, including the apices of the toes and the back of the heel, and are associated with trauma or wearing unsuitable shoes
  • The neuroischaemic foot develops necrosis in the presence of infection or if tissue perfusion is critically diminished
  • Even if neuropathy is present and plantar pressures are high, plantar ulceration is rare. This is probably because the foot does not develop heavy callus, which requires good blood flow.

 

After classification of the diabetic foot, it is necessary to make the appropriate staging in its natural history. The natural history of the diabetic foot can be divided into six stages as shown:

  • Stage 1: Normal foot
  • Stage 2: High-risk foot
  • Stage 3: Ulcerated foot
  • Stage 4: Infected foot
  • Stage 5: Necrotic foot
  • Stage 6: Unsalvageable foot.

 

Stage 1

At this stage, the patient does not have the risk factors of neuropathy, ischaemia, deformity, callus and oedema. The patient is not vulnerable to foot ulcers. The patient’s foot is free of diabetic complications but may be affected by other foot pathologies that occur in the general population. The foot is usually asymptomatic and any problems, including pain, are non-diabetic in nature.

Stage 2

The patient has developed one or more of the risk factors for foot ulceration including neuropathy, ischaemia,deformity, callus and oedema. The major risk factors are neuropathy and ischaemia and it is rare for the other three to cause problems when neuropathy and ischaemia are absent. When they are present, however, all these risk factors need addressing to reduce susceptibility to ulceration. Patients without current active foot ulceration but with a history of previous ulceration should be regarded as at risk.

Within stage 2, there are specific conditions which are non-ulcerative but require treatment. These include:

  • Severe chronic ischaemia
  • Acute ischaemia.

There are also specific complications of neuropathy:

  • Charcot’s osteoarthropathy, including neuropathic fractures
  • Painful neuropathy.

Stage 3

The foot has a skin breakdown. Although this is usually an ulcer, it is important not to underestimate apparently minor injuries such as blisters, skin fissures or grazes, all of which have a propensity to become ulcers if they are not treated correctly and fail to heal quickly. Ulceration is usually on the plantar surface in the neuropathic foot and on the margins in the neuroischaemic foot .

Stage 4

The foot has developed infection, which can complicate both the neuropathic foot  and the neuroischaemic foot .

Stage 5

Necrosis has supervened. In the neuropathic foot, infection is usually the cause. In the neuroischaemic foot, infection is still the most common reason for tissue destruction although ischaemia contributes . In some cases ischaemia alone can lead to necrosis of a previously intact foot, with slow onset of dry necrosis and necrotic toes which appear shrivelled . The diabetic foot in the patient with renal failure (the so-called renal foot) is very prone to develop necrosis, even in the absence of infection.

Stage 6

The foot cannot be saved and will need a major amputation.

Reasons for major amputation:

  • Extensive necrosis which has destroyed the foot
  • Severe infection which puts the patient’s life at risk
  • Agonizing ischaemic pain which cannot be relieved Unstable foot and ankle, usually secondary to Charcot’s osteoarthropathy, which does not respond to external or internal fixation.