![]() However, T3 through T12 cord segments are situated between T3 to T8. Likewise, in the thoracic spinal cord, the first two thoracic cord segments roughly match first two thoracic vertebral levels. However, the C3 through C8 segments of the spinal cords are situated between C3 through C7 bony vertebral levels. In the upper spinal cord, the first two cervical cord segments roughly match the first two cervical vertebral levels. In summary, spinal vertebral and spinal cord segmental levels are not necessarily the same. Injuries below L2 usually involve the cauda equina and represent injuries to spinal roots rather than the spinal cord proper. Injuries to L2 frequently damage the conus. Injuries to T12 and L1 vertebra damage the lumbar cord. Below the conus, there is a spray of spinal roots that is frequently called the cauda equina or horse’s tail. The tip of the spinal cord is called the conus. In human, the spinal cord ends at L2 vertebral level. It contains most of the segments that innervate the hip and legs, as well as the buttocks and anal regions. The lumbosacral spinal cord, however, starts at about T9 and continues only to L2. The lumbosacral vertebra form the remainder of the segments below the vertebrae of the thorax. The spinal roots form the intercostal (between the ribs) nerves that run on the bottom side of the ribs and connect to the intercostal muscles and associated dermatomes. These vertebral segments are also very special because they form the back wall of the pulmonary cavity and the ribs. The thoracic vertebral segments are defined by those that have a rib. The cervical cord innervates the deltoids (C4), biceps (C4-5), wrist extensors (C6), triceps (C7), wrist extensors (C8), and hand muscles (C8-T1). The C3-4 cord contains the phrenic nucleus. The interface between the first and second vertebra is called the atlanto-axis junction. The interface between the occiput and the atlas is called the atlanto-occiput junction. The second cervical vertebra is called the Axis, upon which Atlas pivots. The first cervical vertebra, upon which the head is perched is sometimes called Atlas, after the Greek mythological figure who held up earth. The back of the head is called the Occiput. The first and second cervical segments are special because they hold and pivot the head. The L5 root exits the cord between L1 and S1 bodies. The L1 root exits the spinal cord between L1 and L2 bodies. The T12 root exits the spinal cord between T1 and L1. The first thoracic root or T1 exits the spinal cord between T1 and T2 vertebral bodies. The spinal roots for C2 exit the spinal column at the atlanto-axis. The spinal roots for C1 exit the spinal column at the atlanto-occiput junction. The sacral cord is situated between the T12 to L2 vertebrae, as shown in figure 1 Spinal Roots. The lumbar cord is situated between T9 and T11 vertebrae. For example, the C8 cord segment is situated in the C7 vertebra while the T12 cord is situated in the T8 vertebra. Spinal cord segmental levels are defined by their roots but are not always situated at the corresponding vertebral levels. The spinal cord sends roots that exit the spinal canal between vertebral bodies. ![]() There are 7 cervical (neck), 12 thoracic (chest), 5 lumbar (back), and 5 sacral (tail) vertebrae. The vertebral levels are indicated on the left side while the cord segmental levels are listed for the cervical (red), thoracic (green), lumbar (blue), and sacral (yellow) cord. As shown in the figure to the left (adapted from a spinal anatomy web site at Emory University) the spinal cord segmental levels do not necessarily correspond to the bony segments. The spinal cord itself has “neurological” segmental levels which are defined by the spinal roots that enter and exist the spinal column between each of the vertebral segments. The spine consists of a series of vertebral segments. The spinal cord is situated within the spine. In this article, I will try to explain the currently accepted definitions of spinal cord injury levels and classification.Īnd vertebral levels. Doctors frequently had different definitions of spinal cord injury levels and complete and incomplete injuries. What is the meaning of the different spinal cord injury levels, the definition of complete and incomplete injury, and the different classification of spinal cord injury? In the early 1990’s, there was no single definition of level, completeness of injury, or classification. They may also be told that they are classified according to the American Spinal Injury Association (ASIA) Classification, as a ASIA A, B, C, D, or E. They can sometimes be told that they have a bony fracture or other involvement of one or more spinal vertebral levels. They are often told that the injury is “complete” or “incomplete”. People with spinal cord injury are often told that they have an injury at a given spinal cord level. Keck Center for Collaborative Neuroscience
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