A Spinal Cord Injury (SCI) is typically defined as damage or trauma to the spinal cord that results in a loss or impaired function resulting in reduced mobility or feeling. Typical common causes of damage to the spinal cord are trauma (car and motorcycle accidents, gunshots, falls, sports injuries, etc) or disease (Transverse Myelitis, Polio, Spina Bifida, etc.). Spinal cord injuries are classified according to both the level of injury (the location on the spine) and the completeness of the injury.

High injuries (at the level of the cervical vertebrae) will result in quadriplegia (or tetraplegia); lower level injuries (at the thoracic, lumbar or sacral levels) may result in paraplegia. More precisely, injuries are described by the preserved neurological function, from C1 to S5. A spinal cord injury at C1 will affect all neurological systems below that level; the patient may require the assistance of mechanical ventilation (as even respiratory function could be compromised). A spinal cord injury at the lumbar level, in contrast, would not affect neurological function in the areas of the body corresponding to the cervical or thoracic levels (arm function would be intact, for example).

The completeness of a spinal cord injury relates to the amount of neurological function that is retained below the level of injury. Completeness is assessed according to the American Spinal Injury Association (ASIA) scale, with grades A through E.  A spinal cord injury is assessed as grade A if it is complete: this means that no motor or sensory function remains at the sacral segment S4/5. A grade of B corresponds to an injury where only sensory function – but not motor function – is preserved below the injury. Grades C and D relate to incomplete injuries where some but not all of motor function remains. Grade E corresponds to an injury where both normal sensory and motor function are preserved.

Spinal cord injuries are associated with a higher rate of mortality. The annual mortality rates are positively correlated to higher level injuries and to higher grades of injuries.