In short. How immobility causes pressure ulcers, how they are staged, the prevention that works, and when surgical closure with a flap is needed.
Key points
- Repositioning at planned intervals, pressure-redistributing mattresses and cushions, keeping skin clean and dry, avoiding shear during transfers, and treating malnutrition are the measures with evidence behind them.
- Dressings do not prevent pressure ulcers.
- Once a deep ulcer exists, healing takes months, and recurrence at the same site is common even after good surgical closure.
A pressure ulcer is an area of skin and underlying tissue damaged by sustained pressure, usually over a bony prominence. It forms in people whose mobility is reduced — after a stroke, in advanced illness, with spinal injury, or during a long hospital stay. It is not simply a sign of poor nursing; it is a mechanical injury, and the answer is largely mechanical too.
How pressure causes damage
Sustained pressure above the capillary closing pressure stops blood flowing through the skin. Deprived of oxygen, tissue begins to die within a couple of hours, and the damage continues even after the pressure is removed. Shear and friction add to it when a person slides down a bed or is dragged rather than lifted. Muscle and fat die before skin does, so a small dark mark can sit over a deep cavity — the wound is almost always worse than the surface suggests.
Staging
Stage 1 is intact skin with persistent redness that does not blanch. Stage 2 is partial-thickness loss, a shallow ulcer or blister. Stage 3 is full-thickness loss through to subcutaneous fat, with bone not exposed. Stage 4 is full-thickness loss with exposed bone, tendon, or joint. Deep tissue injury is a separate category: intact skin over a purple or maroon area that is far deeper than it appears. Staging is done after debridement, because dead tissue hides the real depth.
The only effective prevention is movement
Repositioning at planned intervals, pressure-redistributing mattresses and cushions, keeping skin clean and dry, avoiding shear during transfers, and treating malnutrition are the measures with evidence behind them. Dressings do not prevent pressure ulcers. Once a deep ulcer exists, healing takes months, and recurrence at the same site is common even after good surgical closure.
Prevention that works
Risk is assessed formally on admission and whenever the patient’s condition changes. Anyone at risk is turned on a schedule, kept off the damaged area, and given support surfaces that spread load. Nutrition matters: low protein intake and low body weight are strong predictors of breakdown, so dietetic input is part of treatment rather than an optional extra. Continence care protects skin from moisture damage.
When surgical closure is needed
Stage 3 and stage 4 ulcers, and deep tissue injuries that have declared themselves, often need surgical debridement first and reconstruction second. A flap — a block of skin, fat, and often muscle moved with its own blood supply — is the standard closure for a deep defect over bone, because it brings padding and blood into an area that has neither. Timing matters: operating before infection is controlled and nutrition is adequate wastes the operation. Afterwards the reconstructed area must never bear weight or pressure in the way that caused the ulcer, or it will break down again.
Seek urgent review if
- A new area of purple, black, or blistered skin appears over a heel, hip, or the base of the spine.
- An existing ulcer deepens, drains pus, or develops a foul odour or fever.
- A recently closed pressure ulcer reopens or begins to leak fluid.
Frequently asked questions
What actually causes a pressure ulcer?
Sustained pressure above the capillary closing pressure stops blood flowing through the skin, and tissue begins to die within a couple of hours. Shear and friction add to it during transfers. Muscle and fat die before skin, so the wound is usually deeper than the surface suggests.
How are pressure ulcers staged?
Stage 1 is intact skin with redness that does not blanch. Stage 2 is partial-thickness loss. Stage 3 is full-thickness loss to fat, with bone not exposed. Stage 4 exposes bone, tendon or joint. Deep tissue injury is a separate category. Staging is done after debridement.
Do special dressings prevent pressure ulcers?
No. The measures with evidence behind them are repositioning at planned intervals, pressure-redistributing mattresses and cushions, keeping skin clean and dry, avoiding shear during transfers, and treating malnutrition. Once a deep ulcer exists, healing takes months and recurrence at the same site is common.
Risks & Limitations
- Chronic wounds heal over months, not weeks. A wound that closes in three to six months of consistent care is a good result.
- Recurrence is common. Both diabetic foot wounds and venous leg ulcers frequently return, which is why protective footwear and compression continue after healing.
- Partial or complete failure of a skin graft or flap, which may require further surgery.
- Infection and biofilm, which delay healing by weeks and can spread deeply or into bone.
- Amputation risk in diabetes and vascular disease, which is reduced but never abolished by treatment.
- Prolonged dressings and repeated clinic visits. Offloading, compression, and follow-up are demanding and take months.
- Donor-site scarring and discomfort where a graft or flap was taken.
- Reduced or absent sensation in grafted and flap tissue, and around a healed diabetic foot wound.
When to Seek Care
- A wound that is enlarging or deepening, or that begins to expose bone, tendon, or joint.
- Black, grey, or dead tissue appearing in or around the wound.
- Spreading redness, warmth, or swelling around the wound.
- Fever, shivering, or feeling generally very unwell.
- Foul odour or pus from the wound.
- New or severe pain, including pain in the leg or foot at rest or at night.
- A toe or foot that turns black, cold, or blue.
- Loss of sensation in a foot or toe, or a new wound or blister you cannot feel.
References & Further Reading
- World Health Organization (WHO) — chronic wound and diabetes care resources
- NICE (National Institute for Health and Care Excellence) — guidance on wound care, diabetic foot problems, and pressure ulcers
- Wounds International — international consensus documents on wound infection, biofilm, and compression therapy
- American Society of Plastic Surgeons (ASPS) — plastic surgery guidance on wound closure
- Cochrane Library — systematic reviews in wound care and wound closure
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.