Student Pages

Lecturer: Craig Payne

This lecture will cover:

Introduction to diabetic foot complications

Risk factors for diabetic foot complications

Pathophysiology of diabetic foot complications

Introduction to the Diabetic Foot

What is it?
“Infection, ulceration and/or destruction of deep tissues associated with neurological abnormalities and various degrees of peripheral vascular disease in the lower limb” (WHO, 1985)
“The term “diabetic” foot indicates that there are specific qualities about the feet of people with diabetes that sets this disease apart from other conditions that affect the lower extremity” (Habershaw & Chzran, 1995)

However, anything that affects the foot in those with diabetes can affect the foot in those without diabetes. So another definition could be “…the many different lesions of the skin, nails, bone and connective tissue in the foot which occur more often in diabetic patients than non-diabetic patients such as ulcers, neuropathic fractures, infections, gangrene and amputations”(De Heus-van Putten, 1994)

“The term ‘diabetic foot’ implies that the pathophysiological processes of diabetes mellitus does something to the foot that puts it at increased risk for tissue damage”. (Payne & Florkowski, 1998)

The diabetic foot is a group of conditions (or syndrome) in which these pathophysiological process lead to tissue breakdown and the resultant increase in morbidity and maybe amputation.

Natural history of the ‘diabetic foot’:
1. No evidence that the pathophysiological process of diabetes have put the foot at increased risk for tissue damage
2. Evidence that the pathophysiological process of diabetes have put the foot at increased risk for tissue damage
3. Tissue damage has occurred and the foot is at risk for end stage complications (ie amputation)

Of all the complications of the diabetes, those that occur in the foot are considered the most preventable.

Epidemiology:
- 50% of all LEA’s are diabetes related
- >70% of LEA’s are preceded by a foot ulcer
- 3-10% of those with diabetes have a foot ulcer
- 15% of all those with diabetes will, during their lifetime develop an ulcer
- 4/5 of foot ulcer are precipitated by external trauma

Amputations:
• up to 20% undergo an ipsilateral amputation within 12 months
• up to 50% undergo a contralateral amputation within 1-3 years; >50% within 5 years
• 3 year mortality after amputation is 20-50%

Most important risk factors:
- Loss of protective sensation
- Longer duration of diabetes
- Higher foot pressure

Online resources:

ePodiatry's links to diabetic foot websites

Pathophysiology of the diabetic foot

Diabetic foot ulcers

3 broad types:
• neuropathic
• ischaemic
• neuroischaemic

Anatomical distribution: ~50% of ulcers are on the toes; ~30-40% are on the plantar metatarsal head; ~10-15% are on the dorsum of the foot; ~5-10% are on the ankle; up to 10% are multiple ulcers.

Mechanisms of injury that destroy the foot (Tredwell, 1994):
1) Direct mechanical disruption of tissue (eg patient stepping on nail while barefoot abruptly breaking the skin barrier)
2) Small amount of force that is sustained over time that leads to ischaemia (eg tight shoe may lead to breakdown of bunion site)
3) Moderate amount of force that is repeated over and over leads to inflammation and enzymatic autolysis of tissue (eg plantar metatarsal ulceration)
4) Infection

KEY QUESTION:

How do the pathophysiological features of diabetes put the foot at increased risk for tissue damage?

A number of  precipitating events can initiate damage in the foot in those with diabetes that is at increased risk for tissue damage:
- Accidental cuts
- Shoe trauma
- Repetitive stress
- Thermal trauma
- Iatrogenic
- Vascular occlusion
- Skin or nail conditions

Demographic risk factors
- Age (older at greater risk)
- Gender (male is at 2x greater) (mechanism for gender diferences is not clear - maybe behavioural; maybe physiological)
- Ethnicity (some ethnic groups are at signifcantly increased risk for foot complications) (mechanism not clear - maybe behavioural; maybe cultural; maybe physiological; may be linked to socio-economic status; maybe access to health care)
- Social situation (living alone 2x greater risk)

Other risk factors

- Body weight (higher prevalance in those with type 2 diabetes) - however the link to increased plantar pressure is inconsistent; could be related to other DM complications (eg dyslipidaemia)
- Smoking (not linked to foot ulcer in multivariate analysis; Why??)

- Footwear - can be protective (if appropriate) or precipitating (if inappropriate)

Diabetes related risk factors
- Duration of diabetes - highly related to diabetic foot complications; it is highly correlated to other diabetes complications – so which one is really the risk factor?)
- Glycaemic control (univariate studies show a link; multivariate either don’t show a link or a weak link; why?)
- Loss of protective sensation - main risk factor; permissive of unperceived injury
- Motor neuropathy (muscle wasting and gait changes; the “intrinsic minus foot” – high arched, claw toes, intrinsic muscle wasting)
- Autonomic neuropathy - microvascular dysfunction; Anhidrotic, dry, cracked skin
- Peripheral vascular disease (4x more common in those with diabetes)

- Increased plantar pressures
- Limited joint mobility (AGE’s/glycation of collagen; restricts movement of key joints; related to increased plantar pressures; mechanism of increase in plantar pressures unclear; stronger relationship to foot ulcers and pressure in univariate than in multivariate studies)

- Immune/Defence mechanisms (infections are more common; the immune responses are impaird due to vascular supply factors, chemotatic factors and a reduced neutrophil response)

- Previous ulceration (this is THE main risk factor for ulceration)

Behavioural risk factors
Self management skills are highly correlated to the presence of diabetic foot complications

Why? - is it related to their perception of vulnerability, regardless of their actual vulnerability (risk status)

Interaction of risk factors:

Boyko et al, (1999):
“In conclusion, this study demonstrated that multiple mechanisms contribute to the development of diabetic foot ulcer. Because of the interrelatedness of many diabetic complications and associated factors, it may be misleading to consider individual potential risk factors for foot ulcer in future research, as demonstrated in this study, many predictors in univariate analysis will not be shown to have independent effects on ulcer risk”

Online resources:

ePodiatry's links to online articles on diabetic foot complications

Causal pathways for foot ulcers - full text artilce from Diabetes Care

Diabetic Foot Ulcers: Pathogenesis and Management - full text from the American Family Physician

A Review of Causes of Foot Ulceration in Patients with Diabetes Mellitus - full text article from the Journal of Prosthetics and Orthotics

Multicenter study of the incidence of and predictive risk factors for diabetic neuropathic foot ulceration - full text article from Diabetes Care

Diabetic Foot links from Medical Information Directory

Links to:

Lecture 1; Lecture 2 ; Lecture 3 ; Lecture 5 ; Lecture 6