A spinal cord injury (SCI) is damage to the spinal cord that causes changes in its function, either temporary or permanent. These changes translate into loss of muscle function, sensation, or autonomic function in parts of the body served by the spinal cord below the level of the lesion. Injuries can occur at any level of the spinal cord and can be classified as complete injury, a total loss of sensation and muscle function; or incomplete, meaning some nerve signals are able to travel past the injured area of the cord.
Spinal cord injuries generally result in at least some incurable impairment even with the best possible treatment. The best predictor of prognosis is the level and completeness of injury, as measured by the ASIA impairment scale. The neurological score at the initial evaluation done 72 hours after injury is the best predictor of how much function will return. Most people with ASIA scores of A (complete injuries) do not have functional motor recovery, but improvement can occur. Most patients with incomplete injuries recover at least some function.
At each level of the spinal column, spinal nerves branch off from either side of the spinal cord and exit between a pair of vertebrae, to innervate a specific part of the body. The area of skin innervated by a specific spinal nerve is called a dermatome, and the group of muscles innervated by a single spinal nerve is called a myotome. The part of the spinal cord that was damaged corresponds to the spinal nerves at that level and below. Injuries can be cervical 1–8 (C1–C8), thoracic 1–12 (T1–T12), lumbar 1–5 (L1–L5), or sacral (S1–S5).