Diabetes is a systemic disease that affects the vascular, nervous, integumentary & immune systems
Epidemiology
At any one time, 3-4% of patients with DM have a foot ulcer. 15% develop a foot ulcer over their lifetime
When a foot ulcer develops the chance of going on to amputation ↑ 8 fold
P>Pathophysiology
N>Nervous system
Diabetic neuropathy is most common in patients with poor glycaemic control. All branches of the nervous system are affected. Both myelinated & non-myelinated fibres are involved
Sensory neuropathy
predominates
appearing distally in a glove & stocking distribution & progressing proximally
Loss of sensation leads to an inability to respond to mechanical stress
major cause of tissue breakdown in the insensate foot is shear force.
ultimate tensile strength of normal plantar skin is 1200 lb/sq inch. In normal walking average pressures do not exceed 75 lb/sq inch in a barefoot person, 50 lb/sq inch in a person in leather soled shoes, & 25 lb/sq inch in a person using padded, molded inserts.
Pressures as low as 20 lb/sq inch at 10 000 reps/day progressive inflammation develops by day 3 & true ulceration by day 8. Normal people feel pain early in the inflammatory phase & remove the foot, but insensate patients are not able to do this
Pressures as low as 1-2lb/sq inch can block capillary flow, resulting in ischaemia, & these pressures are easily achieved in poor fitting shoes
Autonomic dysfunction
results in a ↓ in sweating. This results in dry, cracked skin. Cracking may allow bacteria to penetrate the skin
Neuropathic skin
tends to produce excessive keratin. Hard callus can form which damages underlying tissues by causing local ↑ in pressure
Motor loss
less common & can affect both the nerve & the motor endplate. Motor loss affects the distal motor nerves most, leading to atrophy of the small muscles of the foot, which becomes manifest as claw toes, with high arches. This results in abnormal pressure distribution which predisposes to plantar ulceration under the prominent metatarsal heads, & corns over the prominent PIPJ
Vascu>Vascular system
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Atherosclerosis
is more common in diabetics, occurs earlier, & affects a higher percentage of women
involvement is more diffuse, more often bilateral & more rapidly progressive
Because the disease is more rapidly progressive, there is less time to develop collateral circulation
Disease affects both small & large vessels.
basement membrane is thicker in the capillaries
large vessels are often occluded at sites of bifurcation or passage through a hiatus, thus at the aortic bifurcation, iliac bifurcation, femoral artery bifurcation & passage through the adductor hiatus. The arteries become calcified & non compressible
Note that the blood supply necessary to allow healing of an ulcer is greater than that needed to maintain intact skin
Immun>Immune system
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Diabetics have altered white cell function, with impaired chemotaxis
They have altered fibroblastic function & ↓ collagen production & strength, which results in impaired wound healing
Osteopo>Osteoporosis
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Generalized osteoporosis of the feet may predispose to insufficiency fractures around the ankle or in the metatarsals
Evaluat>Evaluation
he skin reflects the functional level of circulation & sensation.
Sensati>Sensation
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Qualitative measures of skin sensation
light touch & pin prick sensation
two point discrimination
proprio-ception
Quantitative measures
Semmes Weinstein monofilaments
Semmes Weinstein monofilament 5.07 (represents 10g of pressure) will predict most accurately the likelihood of a patient developing an ulcer
90% of patients that can feel this monofilament will not develop ulcers
However, if the patient has previously had an ulcer, this is the best predictor of the likelihood of developing another
Biothesiometer
a device that delivers a measured reproducible vibratory stimulus, but has problems with inconstant applied pressures
Vascula>Vascular
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Qualitative measures
evaluation of the skin temperature
capillary refill
pulses
hair & nail growth
Quantitative measures
measurement of the ankle brachial indices, s
skin perfusion pressure
transcutaneous oxygen diffusion
Arterial Doppler measurements
If a patient obviously has ischaemia but the ABI (ankle to brachial arterial index) is 1.0 or higher this suggests stiffening of the vessel wall by calcification rather than good flow. There should be a level of 0.45 or greater
Doppler flow study will also show pulsatile flow tracings & not the normal triphasic wave forms seen in non calcified vessels
Skin perfusion pressure can be measured using a photodetector pressed against the skin by a manometer. The pressure is read at the time of skin reddening as the pressure is released. Pressures of 31-40mmHg have been associated with an 85% rate of healing
Transcutaneous PO2 measurements are probably the best measurement of healing potential. They are performed at standardized points on the foot using a neonatal sats probe. Prior to performing the test the skin should be heated to 45° for 10 minutes
Levels below 20mmHg indicate a poor healing potential (less than 50%)
Levels from 20-29 mm Hg have a 75% healing rate
Levels greater than 30mmHg have a 92% healing rate
Given a PO2 of 35mmHg at mid foot a transmetatarsal ampu-tation should heal
TcPO2 level is adversely affected by cellulitis & oedema
Charcot >Charcot joints
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occur in less than 1% of diabetic patients
(but diabetes is the commonest cause of a neuropathic joint in western countries, leprosy & tertiary syphilis being more common worldwide)
Affected patients are more likely to be insulin dependent
30% of cases are bilateral
most commonly affected joints are the midfoot (60%) then the hindfoot (30%).
In the hindfoot, the typical deformity is in varus, which makes the lateral malleolus prominent
presentation may be insidious, with a progressive flatfoot deformity, or may be acute, mimicking infection
The differentiation can be made by elevating the foot above heart level, when the swelling & erythema secondary to the Charcot joint should rapidly settle, & by following the inflammatory markers
diagnosis can also be helped by using a combination of technetium & indium-111 scans
Treatmen>Treatment
lass="wp-block-heading">Diabetic>Diabetic foot caree most important component of diabetic foot care is patient education.
Regular inspection of the foot to rule out ulcers/callosities/bruises/cuts
Feel the limb for any warmth or heat
Hydration of skin
15-20 minute soaks, plain water, room temperature
Oiling of skin (lanolin best). This will help to keep the skin hydrated, & callus moist & thereby supple
Debridement of callus
This should be done daily by the patient & may need to be done fortnightly or monthly by the podiatrist
digits need to be put through a range of motion to prevent contracture
Other pointers in diabetic foot care
Adequate shoes – no patient with a neuropathic foot should go without shoes. Grace Warren says the best insole is 150 shore microcellular rubber (MCR), ideally 6mm thick
Use white socks; this makes it easier for the patient to see areas of discharge
Positional adjustments are necessary
Management>Management of ulceration
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Ulceration is caused by a combination of pressure & neuropathy
pressure is often applied to a bony prominence
When neuropathic ulcers are unroofed the underlying granulation tissue is usually healthy
Ischaemic ulcers often have necrotic tissue in their bases, & patients with ischaemic ulcers need a vascular consultation to see if the limb can be saved. Ischaemic ulcers typically need angioplasty or bypass surgery to achieve healing
70-90% of neuropathic ulcers occur in the forefoot
first step in the management of diabetic foot ulcers is optical medical management of the diabetes with good glycaemic control
Grade O “ulcers”
treated by pressure relief
Surgical excision of bony prominences should be considered if non-operative measures are inadequate, assuming the patient has adequate blood supply to allow healing
Grade 1 & 2 lesions
can be treated with a total contact cast
Myerson used the total contact cast in the treatment of these lesions with a 90% healing rate at 6 weeks
There was however a 30% relapse rate over the 18 month followup period, but 80% of these ulcers healed in a second cast after two weeks of treatment
Role of hyperbaric oxygen therapy
Use is controversial, but has been shown to be beneficial in patients with a positive oxygen challenge (↑ in transcutaneous oxygen tension when breathing 100% oxygen)
Achilles tenotomy
Patients often develop an Achilles contracture which leads to ↑ forefoot pressures. Tenotomy may benefit these patients
Infection
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commonest organisms are S. aureus, Streptococcus species, Enterococcus organisms & S. epidermidis
Commonly isolated gram negative organisms include Proteus & Pseudomonas
Anaerobes are cultured in around 1/3
most specific investigation for osteomyelitis is an Indium 111 labeled white cell scan
In treating infections, the appropriate antibiotics plus or minus surgery are used
Areas that are poorly vascularized or necrotic need to be debrided/amputated to the level of viable tissue
characterized by fragmentation & presents as a fracture, or ligamentous disruption. Treatment should be by elevation for 1-2 days, then total contact casting. Weight bearing is not allowed until the inflammatory phase is over, which takes several months
Stage II
characterized by coalescence. Fragmentation gradually stops on a series of X-rays. The patient is allowed to progress to weight bearing in a total contact cast
Stage III
characterized by bone consolidation & healing. Stages II & III typically last 18-24 months.
Management of calc>Management of calcaneal osteomyelitis
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This depends on adequate blood flow
If there is adequate blood flow, debridement, IV ABs & total contact cast
If there is not, below knee amputation. Symes or Boyd amputation is contra-indicated
Management of frac>Management of fractures
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Most common fracture is of the Lisfranc joint
Fractures should be managed closed if possible with a full contact cast extending to past the toes, until there is demonstration of healing & tissue homeostasis is returning
