Neuropathic Foot

Neuropathic Foot

Fig. 1.10 (a) Neuropathic foot with high medial longitudinal arch. In severe cases, pressure points develop over the apices and dorsal interphalangeal joints of claw toes, (b) Claw toes in neuropathic foot.

Fig. 1.10 (a) Neuropathic foot with high medial longitudinal arch. In severe cases, pressure points develop over the apices and dorsal interphalangeal joints of claw toes, (b) Claw toes in neuropathic foot.

buckles at a given force of 10 g. Ability to feel that level of pressure provides protective sensation against foot ulceration. It is helpful first to demonstrate the technique on the patient's forearm.

The number of sites used varies according to different protocols. Sites examined include the plantar aspects of the first toe, the first, third and fifth metatarsal heads, the plantar surface of the heel and the dorsum of the foot. The filament should not be applied at any site until callus has been removed. If the patient cannot feel the filament at any of the tested areas, then protective pain sensation is lost, indicating susceptibility to foot ulceration (Fig. 1.12). The 10-g monofilament may become overstrained and inaccurate after use on numerous occasions and should be replaced regularly. A recent study has assessed differences in the performance of commercially available 10-g

Autonomic Neuropathic
Fig. 1.11 Distended veins secondary to autonomic neuropathy.
Autonomic Neuropathy The Foot
Fig. 1.12 A monofilament is applied perpendicular to the foot and pressed until it buckles at a given force of 10 g.

monofilaments. Monofilaments were tested using a calibrated load cell. Each monofilament was subjected to 10 mechanical bucklings of 10 mm while the load cell detected the maximal buckling force. Longevity testing was performed on a subset of the monofilaments by subjecting them to continuous compression until the buckling force was less than 9 g. Longevity and recovery testing suggest that each monofilament would survive usage on 10 patients before needing a recovery time of 24 h before further usage.

If filaments are not available, then a simple clinical examination detecting sensation to light touch using a cotton wisp and vibration using a 128-Hz tuning fork will suffice. It is best to compare a proximal site with a distal site to confirm a symmetrical stocking-like distribution of the neuropathy, and to avoid the use of 'pin-prick' to detect sensory loss.

Other useful but simple and practical tests for detecting neuropathy, if health-care practitioners have no access to formal equipment, include the Achilles tendon pinch, and the application of vertical pressure onto the nail plate. In practice, any patient who walks on a foot with ulceration or heavy plantar callus without concern has significant neuropathy.

Footwear assessment

It is important to examine both shoes and socks.

Examination of patient's footwear

• Is the toe box broad and deep enough?

• Does the shoe fasten with a lace or strap? 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 whole of tread suggesting pes cavus?

Examination of patient's socks

• Are the socks large enough?

• Are the seams too prominent?

• Are the socks in good repair—no 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

• Eyes: Visual acuity Fundi.

(A patient lacking necessary visual acuity to give himself a

Optical Pedobarograph Device
Fig. 1.13 The neurothesiometer.

daily foot examination is a patient at risk, and his family or caregiver should help him.)

Investigations

Investigations include:

• Neurological

• Skin temperature

• Laboratory

• Radiological

Neurological

The degree of neuropathy can be quantified by the use of the biothesiometer or the more recentiy available neuro-thesiometer (Fig. 1.13). Both are devices which, when applied to the foot, deliver a vibratory stimulus, which increases as the voltage is raised. The vibration threshold increases with age, and for practical purposes, any patient unable to feel a vibratory stimulus of 25 volts is at risk of ulceration.

A small number of patients have a small-fibre neuropathy with impaired pain and temperature perception but with intact touch and vibration. They are prone to ulceration and thermal traumas but test normally with filaments and biothesiometer, and a clinical assessment of light touch and vibration is normal. As yet, there is no simple inexpensive method of detecting and quantifying small-fibre neuropathy. However, a simple temperature assessment of cold sensation can be made by placing a cold tuning fork on the patient's foot and leg.

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 and this has important implications for management, namely that macrovascular disease is not an important factor and further vascular investigations are not necessary.

Many diabetic patients have medial arterial calcification, giving an artificially elevated systolic pressure, even in the presence of ischaemia. It is thus difficult to assess the diabetic foot when the pulses are not palpable, but the pressure index is > 1. There are two explanations.

• The examiner may have missed the pulses, particularly in an oedematous foot, and should go back to palpate the foot after the arteries have been located by Doppler ultrasound

• If the pulses remain impalpable, then ischaemia probably exists in the presence of medial wall calcification. It is then necessary to use other methods to assess flow in the arteries of the foot, such as examining the pattern of the Doppler arterial waveform or measuring transcutaneous oxygen tension or toe systolic pressures. Furthermore, absence of foot pulses would be an indication to investigate popliteal and femoral arteries.

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 (Fig. 1.14). 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)

• Serum electrolytes, urea and creatinine (to assess baseline renal function)

• Serum bilirubin, alkaline phosphatase, gamma glutamyl transferase, aspartate transaminase (to assess baseline liver function)

Digital Skin Thermometer
Fig. 1.14 Digital skin thermometer.

• Blood glucose and HbAlc (to assess diabetic control)

• Serum cholesterol and triglycerides (to assess arterial disease risk factors).

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

Foot pressures

These techniques measure the pressure distribution on the plantar surface of the foot. There are two main methods: 'out-of-shoe'. and 'in-shoe'. The introduction of the optical pedobarograph considerably improved the accuracy of out-of-shoe pressure measurements. Developments in computer technology have led to microprocessor-like recording devices to quantify in-shoe foot pressures and these include the EMED system and the F Scan system. These systems have the possibility of identifying patients at risk of plantar neuropathic ulceration and give a basis for the implementation of footwear adjustments or surgical intervention. We have found that they are also useful educational tools as described in Chapter 3.

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Responses

  • melody
    How to use a neurothesiometer?
    7 years ago

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