Spinal cord injuries (SCIs) can be classified based on function (how much feeling and movement you have) or on where the damage occurred. When a nerve in the spinal cord is injured, the nerve location and number are often used to describe how much damage there is. For example, a C7 injury is associated with the seventh cervical nerve of the neck and its effect on feeling and movement. C7 is known as the functional level of injury. People who have SCIs often use these classifications to describe themselves.

SCIs are also described as complete and incomplete. An incomplete injury is further classified into four subsections. The American Spinal Injury Association (ASIA) classifies these injuries as follows:

• A (complete). There is no feeling or movement of the areas of your body that are controlled by your lowest sacral nerves. This means that you don't have feeling around the anus. You can't control the muscle that closes the anus. People with complete spinal cord injuries don't have control of bowel and bladder function.
• B (incomplete). There is feeling but no movement below the level of injury, including sacral segments that control bowel and bladder function.
• C (incomplete). There is feeling and movement below the level of injury. More than half of key muscles can move, but not against gravity. Moving against gravity means moving up. An example is raising your hand to your mouth when you are sitting up.
• D (incomplete). There is feeling and movement below the level of injury. More than half of key muscles can move against gravity.
• E (Feeling and movement are normal).

What parts of the body are affected by a spinal cord injury (SCI)?

The spinal cord is surrounded by protective rings of bone called vertebrae. The vertebrae and spinal nerves are organized into segments, starting at the top of the spinal cord. Within each segment, the vertebrae and nerves are numbered. The segments are as follows:

• Cervical. The neck area contains 7 cervical vertebrae (C1 through C7) and 8 cervical nerves (C1 through C8). Cervical spinal cord injuries (SCIs) usually cause loss of function in the chest, arms, and legs. Cervical injuries can also affect breathing and bowel and bladder control.
• Thoracic. The chest area contains 12 thoracic vertebrae (T1 through T12) and 12 thoracic nerves (T1 through T12). The first thoracic vertebra, T1, is where the top rib attaches to the spine. Thoracic SCIs usually affect the chest and the legs. Injuries to the upper thoracic area can affect breathing. Thoracic injuries can also affect bowel and bladder control.
• Lumbar. The lumbar area (between the chest area and the pelvis) contains 5 lumbar vertebrae (L1 through L5) and 5 lumbar nerves (L1 through L5). Lumbar SCIs usually affect the hips and legs. Lumbar injuries can also affect bowel and bladder control.
• Sacral. The sacral area (from the pelvis to the end of the spine) contains 5 sacral vertebrae (S1 through S5) and 5 sacral nerves (S1 through S5). Sacral SCIs usually affect the hips and legs. Injuries to the upper sacral area can also affect bowel and bladder control.

The higher the damage occurs on the spinal cord, the more of the body is affected. This is because the nerves in the area of a vertebra control body parts in that area. When the spinal cord is damaged, messages can't "jump over" the damaged area. This means that messages sent from the brain can't make it to body parts below the damaged area, and vice versa. So the body at and below the level of injury is affected.

For example, in an injury to the spinal nerves in the neck area (C1 through C8), messages are stopped in the neck area. This usually causes at least some paralysis of the chest, arms, and legs (tetraplegia, also known as quadriplegia). In an L3 injury, messages are stopped at the lower back. This causes at least some paralysis of the legs and hips (paraplegia).