Diabetic Foot Ulcers: Causes, Risks and Treatment

A diabetic foot ulcer is an open wound on the foot of someone with diabetes. The skin has broken down through at least its top layer. Most are caused by nerve damage, poor circulation or both, and they can become serious quickly if infected. Below, we explain causes, types, checks and treatment.

What is a diabetic foot ulcer?

A foot ulcer is a break in the skin of the foot. It goes through the outer layer (the epidermis) and into at least part of the layer beneath (the dermis).³ In diabetes, it usually comes with nerve damage in the feet (peripheral neuropathy), narrowed leg arteries (peripheral artery disease) or both.³

A superficial ulcer stays within the skin. A deep ulcer reaches tissue underneath, such as fascia (a tough sheet of tissue), muscle, tendon or bone.³ NICE, which sets guidance for the NHS, counts an ulcer as an 'active diabetic foot problem'. So are infection, gangrene (dead tissue) and a suspected Charcot foot.¹

Some warning signs can come before an ulcer: bleeding into or under the skin, a blister, or a shallow crack that has not yet reached the deeper layer.³ Our guide to blisters, calluses and other skin warning signs explains how to deal with them safely.

Why do foot ulcers form in diabetes?

Most ulcers start when an at-risk foot meets a trigger, such as a rubbing shoe or stepping on something sharp.² Over time, high blood sugar can damage the small blood vessels and nerves in your feet. So you may not feel an injury, and wounds may heal more slowly.⁵

It often happens like this²:

1. Nerve damage leaves the foot numb and can sometimes change its shape.
2. Numbness, a change in foot shape and stiff joints put extra pressure on parts of the sole.
3. The pressure causes hard skin (callus), which adds more pressure.
4. Bleeding starts under the callus, then the skin breaks down into an ulcer.

Walking on a foot you cannot feel keeps pressure on the wound and slows healing.² Narrowed leg arteries affect up to half of people with a diabetes-related foot ulcer. They make poor healing, gangrene and amputation more likely.²

Neuropathic, ischaemic and neuroischaemic ulcers

Ulcers are grouped by their cause, because this affects treatment. Neuropathic means caused by nerve damage. Ischaemia means reduced blood supply.

These groups come from international guidance.²³ A painless ulcer is not a minor ulcer. In neuroischaemic ulcers, nerve damage can hide the warning signs even when blood flow is badly reduced.²

Where on the foot do ulcers appear?

Ulcers form where your foot takes the most pressure or rubbing. Common places are the ball of the foot (over the metatarsal heads), the big toe, the tips of clawed or hammer toes, and the heel. Ulcers on the sides or top of the foot are often caused by shoes rubbing.⁷

Heel ulcers are less common than ulcers at the front of the foot, but harder to take pressure off and to heal.⁷ Heels are especially at risk if you have to stay in bed. So people at moderate or high risk who go into hospital should have their heels protected from pressure.¹

Can a diabetic foot ulcer be life-threatening?

Sometimes, yes, but quick care lowers the risk a great deal. The danger usually comes from infection spreading from the wound. Sepsis is a serious reaction to infection that can be life-threatening and needs urgent hospital treatment.⁶

Problems that threaten the leg or life need hospital care straight away. They include an ulcer with a fever or signs of sepsis, an ulcer with poor blood supply to the leg (limb ischaemia), a suspected deep infection, and gangrene.¹

Foot ulcers and infections can sometimes lead to an operation to remove a foot or leg.⁸ One NHS trust leaflet also links foot ulcers in diabetes with a higher risk of heart attack, stroke, amputation and early death.⁹ Your doctor should also check for heart and circulation disease that has not been diagnosed yet.¹

Diabetes UK says people with diabetes are up to 20 times more likely to have an amputation. Getting the right treatment early can lower the risk of an ulcer getting worse, becoming infected or leading to amputation.⁵

How is a foot ulcer assessed?

Your team should record the size, depth and position of every ulcer, using a standard system such as SINBAD (Site, Ischaemia, Neuropathy, Bacterial infection, Area, Depth) or the University of Texas classification.¹ SINBAD is recommended for sharing information between professionals, with each item described rather than just a total score.⁴

The team will usually check:

• Blood supply: the pulses in your foot, blood flow sounds using a Doppler (a small ultrasound probe), and ankle or toe pressures.²
• Feeling: whether you can still feel enough to protect your foot, for example with a 10 g monofilament (a fine nylon thread).¹
• Infection: at least two signs of inflammation, such as redness, warmth, swelling or tenderness, or pus. Nerve damage or poor circulation can make these signs weaker.²
• Depth and bone: whether bone can be felt with a sterile metal probe (the probe-to-bone test). Ulcers deeper than the skin need an X-ray.²
• Cause and general health: your shoes, how you walk, foot shape, kidney function, nutrition and blood sugar control.²

Read more about spotting and grading an early stage diabetic foot ulcer. If you have an ulcer, you should be referred within 1 working day to a hospital foot team (the multidisciplinary foot care service) or foot protection service. That team should then assess how urgent your ulcer is within another working day.¹

How are diabetic foot ulcers treated?

Standard ulcer care has five parts¹: offloading (taking pressure off the wound), treating infection, treating poor blood supply, debridement (removing dead tissue and callus) and dressings.

• Offloading: for many ulcers on the sole, the first choice is a knee-high cast or boot that cannot be taken off.⁷
• Treating infection: antibiotics are used when there is an infection, guided by tissue samples. They should not be given just to prevent infection.¹ See how a diabetic foot infection is recognised and graded. For a complex infection, the team may arrange an infectious diseases specialist review.
• Improving blood flow: checking your circulation and, if needed, revascularisation (a procedure to open or bypass narrowed arteries).²
• Debridement and dressings: done by trained professionals, with dressings chosen to suit the wound.¹

Each step is explained in our full guide to diabetic foot ulcer treatment and healing time. For care between appointments, see looking after a foot ulcer dressing at home.

Healing, remission and preventing a new ulcer

An ulcer has healed when the skin has fully closed and nothing is leaking. The foot is then 'in remission', meaning the skin is unbroken and there is no infection anywhere on the foot.³ A new ulcer in someone who has had one before is called a recurrent ulcer, wherever it appears.³

After a diabetic foot ulcer, your risk of another is at its highest, so you will need to protect your feet for life.² In the UK, a past ulcer puts you in the high-risk group. The foot protection service should look after you, with reviews as often as every 1 to 2 months when there is no immediate concern.¹ Check your feet every day and wear footwear that takes pressure off. Never wear the shoe that caused the ulcer again.²