Spinal Cord Injury Levels and Classification
Written by Andrew Sarski on July 30, 2013
When a patient suffers a serious injury of the neck, back or spinal cord, they are often told that they have an injury at a certain spinal cord level, which is further qualified by the severity of the injury: complete or incomplete. Because the location and severity of a spinal cord injury determines what motor and sensory functions may be compromised and whether or not they may return in the future, it’s important to understand the spinal cord injury levels and classification of spinal cord injuries. Spinal cord injuries can be extremely devastating, sometimes resulting in long-term disability or permanent paralysis, costly medical bills, and a decreased quality of life. If you or a loved one has suffered from a spinal cord injury caused by an accident, such as in a motor vehicle accident or slip and fall accident, contact an experienced personal injury attorney to discuss your legal options.
The spinal cord is located within the spine, which consists of a series of vertebral segments. The spinal cord itself has neurological segmental levels, defined by the spinal roots that enter and exist in the spinal column between each of the vertebral segments. There are 29 vertebral segments: seven cervical (neck), 12 thoracic (chest), five lumbar (back), and five sacral (tail), and they do not necessarily correspond with the spinal cord segments. For example, while the C1 cord is situated at the C1 vertebra, the C8 cord is actually situated at the C7 vertebra. Similarly, while the T1 cord is located at the T1 vertebra, the T12 cord is located at the T8 vertebra.
Cervical cord – The first and second cervical segments are important because these are what hold the head. The C3 cord contains the phrenic nucleus. The cervical cord supplies nerves to the deltoids (C4), the biceps (C4-5), wrist extensors (C6), triceps (C7), finger extensors (C8), and hand muscles (C8-T1).
Thoracic cord – The thoracic vertebral segments are defined by those that have a rib, and are important because they form the back wall of the pulmonary cavity and the ribs. The spinal roots form the nerves that run on the bottom side of the ribs, and these nerves control the muscles between the ribs and the associated patches of skin (dermatomes).
Lumbosacral cord – The lumbosacral vertebra form the remainder of the segments below the thoracic vertebra. The lumbosacral cord, however, begins at about T9 and continues only to L2. It contains most of the segments that supply nerves to the hip and legs, as well as the buttocks and anal regions. The L2 supplies nerves to the hip flexors, L3 to the knee extensors (quadriceps), L4 to the ankle dorsiflexors, L5 to the long toe extensors, and S1 to the ankle plantar flexors. The S4-5 cord supplies nerves to the anal sphincter, which represents the end of the spinal cord.
Cauda equina – In humans, the spinal cord ends at the L2 vertebra level, and the tip of the spinal cord is called the conus. Below the conus, there is a collection of spinal roots that is frequently called the cauda equina, or horse’s tail. Injuries to the T12 and L1 vertebra damage the lumbar cord, while injuries to L2 frequently damage the conus. Injuries below L2 usually involve the cauda equina, and represent injuries to spinal roots rather than the spinal cord itself.
Classifying the Severity of Spinal Cord Injuries
Traditionally, spinal cord injuries have been classified as either “complete” or “incomplete,” definitions which have since been found to be weak and ambiguous. In order to more accurately define the severity of a spinal cord injury, the following scale, called the ASIA (American Spinal Injury Association) Impairment Scale, was developed to grade the severity of neurological loss.
- A = Complete: No motor or sensory function preserved in the sacral segments S4-S5
- B = Incomplete: Sensory but not motor function is preserved below the neurological level and includes the sacral segments S4-S5
- C = Incomplete: Motor function is preserved below the neurological level, and more than half of key muscles below the neurological level have a muscle grade less than 3
- D = Incomplete: Motor function is preserved below the neurological level, and at least half of key muscles below the neurological level have a muscle grade of 3 or more
- E = Normal: Motor and sensory function are normal
The most common cervical spinal injuries involve C4 or C5, which typically affect movement and sensation in the arms. For example, a burst fracture of the C5 vertebra may injure the C6 spinal cord, as well as the C4 spinal roots that exist in the spinal column between the C4 and C5 vertebra. An injury of this kind would cause a loss of sensation in the C4 dermatome and would also cause weak deltoids (C4) due to injury to the C4 roots. The biceps (C5) may initially be weak because of swelling of the spinal cord, but should recover. The wrist extensors (C6) however, would remain weak and sensation at and below C6 would be severely compromised.