The exact effects of a spinal cord injury vary according to the type and level injury, and can be organized into two types:
In a complete injury, there is no function below the “neurological” level, defined as the lowest level that has intact neurological function. If a person has some level below which there is no motor and sensory function, the injury is said to be “complete”. Recent evidence suggest that less than 5% of people with “complete” spinal cord injury recover locomotion.
A person with an incomplete injury retains some sensation or movement below the level of the injury. The lowest spinal cord level is S4-5, representing the anal sphincter and peri-anal sensation. So, if a person is able to contract the anal sphincter voluntarily or is able to feel peri-anal pinprick or touch, the injury is said to be “incomplete”. Recent evidence suggest that over 95% of people with “incomplete” spinal cord injury recover some locomotory ability.
The American Spinal Cord Injury Association or ASIA defined an international classification based on neurological levels, touch and pinprick sensations tested in each dermatome, and strength of ten key muscles on each side of the body, i.e. shoulder shrug (C4), elbow flexion (C5), wrist extension (C6), elbow extension (C7), hip flexion (L2). Traumatic spinal cord injury is classified into five types by the American Spinal Injury Association and the International Spinal Cord Injury Classification System.
A indicates a “complete” spinal cord injury where no motor or sensory function is preserved in the sacral segments S4-S5. Since the S4-S5 segment is the lower segmental, absence of motor and sensory function indicates “complete” spinal cord injury.
B indicates an “incomplete” spinal cord injury where sensory but not motor function is preserved below the neurological level and includes the sacral segments S4-S5. This is typically a transient phase and if the person recovers any motor function below the neurological level, that person essentially becomes a motor incomplete, i.e. ASIA C or D.
C indicates an “incomplete” spinal cord injury where motor function is preserved below the neurological level and more than half of key muscles below the neurological level have a muscle grade of less than 3.
D indicates an “incomplete” spinal cord injury where motor function is preserved below the neurological level and at least half of the key muscles below the neurological level have a muscle grade of 3 or more.
E indicates “normal” where motor and sensory scores are normal. Note that it is possible to have spinal cord injury and neurological deficit with completely normal motor and sensory scores.