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10. Understand at what levels spinal nerves exit intervertebral foramina, and how knowledge of this can allow a better understanding of the clinical presentation of herniated discs.
10. Understand at what levels spinal nerves exit intervertebral foramina, and how knowledge of this can allow a better understanding of the clinical presentation of herniated discs.
Spinal nerves typically exit the vertebral column through intervertebral foramina inferior to the same-numbered vertebra.
For example, the T7 spinal nerve exits the column between the T7 & T8 vertebrae. Another example includes the L5 spinal nerve exits the vertebral column between the L5 & S1 vertebrae.
The main exception is in the cervical region. There are 8 cervical spinal nerves and only 7 cervical vertebrae. Cervical spinal nerves exit the vertebral column superior to the same-numbered vertebra. For example, the C1 spinal nerve exits the vertebral column between the skull & C1, C2 spinal nerve exits between C1 & C2 vertebrae, and C8 spinal nerve exits between C7 & T1 vertebrae.
Intervertebral disc herniations (i.e. disc herniation, slipped disc) typically involve the nucleus pulposus protruding through the anulus fibrosus in a posterolateral direction. Due to close proximity, the spinal cord, spinal nerve rootlets and roots, and spinal nerves may be compressed in this disorder and can cause back pain (although this is certainly not the only cause of back pain).
These types of herniations most typically occur in the cervical or lumbar region, particularly involving the intervertebral discs between L4-L5 and L5-S1.
To determine which spinal nerve may be compressed in an IV disc herniation, consider that:
Intervertebral discs neighbor and often form a wall of the intervertebral foramen
Spinal nerves typically exit the vertebral column in the superior most portion of the intervertebral foramen
Thus, a herniation in a posterolateral direction (which is most typical) will avoid the superior most portion of the neighboring intervertebral foramen and not compress that spinal nerve
In other words, a herniated disc may compress the spinal nerve located in the intervertebral foramen inferior to (not neighboring) the IV disc
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