When a normal, healthy person lies or sits in one position for a long time he begins to feel uncomfortable, which makes him/her move or roll over to let another part of his body bear his weight. A person with a spinal injury :

• fails to respond to warnings of pain or discomfort due to loss of sensation and
• secondly is unable to move or roll over to relieve pressure,

These two points that make them at a very high risk of developing pressure sores.