Diabetic Foot Gangrene: Causes and Amputation Risk

Diabetic foot gangrene means an area of tissue in your foot has died. This is most often because its blood supply is blocked, because of infection, or both.¹² It is serious, but understanding it can help you act quickly and make sense of any treatment you are offered. This article is part of our diabetic foot infection guide. It explains gangrene, why amputations happen and how care teams work to save limbs.

What is diabetic foot gangrene?

Gangrene happens when body tissue dies because it is not getting enough blood, because of infection or because of an injury.¹ Dead tissue is also called necrosis. In the foot, gangrene most often affects the toes, the heel or the edges of an ulcer.

The NHS lists these symptoms²:

• skin turning dark red, purple or black, which can be harder to see on brown or black skin
• nearby skin that feels numb or cold, sometimes with swelling
• pain that builds slowly, or comes on suddenly and is severe
• blisters or sores that leak foul-smelling pus or blood

Long-term high blood glucose, peripheral arterial disease (narrowed leg arteries) and a weakened immune system all raise your risk.²

Dry or wet diabetic foot gangrene: what is the difference?

These descriptions follow IWGDF definitions and NHS advice.¹² In wet gangrene the dead tissue is infected and starts to decay (putrefaction), so it can spread and make you seriously ill.

How poor blood flow and infection lead to tissue death

Most foot ulcers in diabetes are caused by nerve damage, poor blood flow (ischaemia) or both.³ Up to half of people with a foot ulcer have peripheral artery disease. It is an important risk factor for slow healing, gangrene and amputation.³ Without enough blood, tissue cannot heal or fight infection.

Infection makes things worse. Infection and artery disease together are linked with a much higher risk of poor healing and amputation.⁴ Infection can also cause fast, destructive (necrotising) damage to the soft tissues, which needs urgent surgery.⁴

Why does diabetes lead to foot amputations?

NICE, which sets guidance for the NHS, notes that diabetes is the most common cause of amputations that are not caused by an injury. It also notes that diabetic foot ulcers come before more than 80% of amputations in people with diabetes.⁵ In the UK, more than 7,000 diabetes-related amputations are reported each year.⁵ Foot infections are the most common event leading directly to a lower-limb amputation.⁴

The hopeful message is that most amputations start with a problem that can be spotted and treated: an ulcer. Getting ulcers and infections treated quickly is the main way to lower this risk.³

Limb salvage: how fast team care protects the foot

Limb salvage means using every suitable treatment to keep as much of the leg and foot as possible. NICE treats some problems as a threat to the limb or to life. These include gangrene, an ulcer with a very poor blood supply (limb ischaemia), deep infection and an ulcer with signs of sepsis. They need immediate referral to hospital emergency care and to the hospital foot team (the multidisciplinary foot care service).⁶

The main parts of care are:

• urgent assessment by a surgeon and a vascular (blood vessel) specialist when infection or gangrene comes with artery disease, to plan drainage and any procedure to restore blood flow (revascularisation)⁴
• removing dead and infected tissue quickly, with early surgery considered within 24 to 48 hours for a moderate or severe infection⁴
• antibiotics guided by tissue samples (cultures), together with taking pressure off the foot (offloading) and wound care, as described in our guide to diabetic foot ulcer treatment

The IWGDF reports that putting these prevention and treatment principles into practice is linked with fewer diabetes-related amputations.³

Minor and major amputation

With diabetic foot gangrene, removing tissue is sometimes the safest way to control infection or let the wound heal. The IWGDF defines two levels¹:

• Minor amputation: any removal through or below the ankle, such as part of a toe, a whole toe or part of the foot.
• Major amputation: any removal above the ankle, such as a below-knee or above-knee amputation.

A minor amputation can help you keep walking and avoid a bigger operation. The NHS says amputation is considered when other treatments have not worked or are unlikely to help.²

Life after amputation and protecting the other foot

After an amputation for diabetic foot gangrene, rehabilitation usually starts the day after surgery, with physiotherapy and occupational therapy. A prosthetist (a specialist in artificial limbs) will talk to you about the options, although an artificial limb does not suit everyone.⁷ Phantom limb pain, and feelings such as grief or low mood, are common and can be treated. Talk to your care team about them.⁷

Looking after your other foot matters, especially if diabetes was the cause. The NHS advises avoiding injury to your remaining leg, wearing well-fitting footwear and seeing a podiatrist regularly.⁷ After a first amputation, people with diabetes are twice as likely as people without diabetes to need another.⁵ That is why regular foot checks matter.