Pressure Ulcers and Staging

What is a Pressure Ulcer?



A pressure ulcer is localized injury to the skin and/or underlying tissue usually over a bony prominence, as a result of pressure, or pressure in combination with shear.

  • Pressure - Pressure is the force per unit surface area that is applied vertically or perpendicular to the surface of the skin. Pressure deforms underlying tissue and compresses small blood vessels hindering blood flow and nutrient supply. Tissues become ischemic and are damaged or die.
  • Shear - Shear is the force per unit surface area applied parallel to the skin surface. Shear occurs when one layer of tissue slides horizontally over another, deforming adipose and muscle tissue, and disrupting blood flow.

A number of contributing or confounding factors are also associated with pressure ulcers; the significance of these factors is yet to be fully elucidated.


  1. National Pressure Ulcer Advisory Panel and European Pressure Ulcer Advisory Panel. (2009). Prevention and treatment of pressure ulcers: clinical practice guideline. Washington DC: National Pressure Ulcer Advisory Panel.