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The canine spinal anatomy is very similar to ours, with the exception of 1 additional thoracic vertebra and 2 additional lumbar vertebra...

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Canine Anatomy

The spinal column is made up of four major vertebral regions: cervical (neck), thoracic (mid back), lumbar (low back) and sacral (pelvic). Dogs have seven cervical, thirteen thoracic, seven lumbar and three sacral vertebrae. There are also variable numbers of coccygeal or tail vertebrae. Intervertebral disks are located between the vertebral bodies starting at the second and third cervical vertebrae (C2-3) and extending to the seventh lumbar and first sacral vertebrae (L7-S1). The three sacral vertebrae are fused and therefore do not have disks. Intervertebral disks are present between the coccygeal vertebra as well, but are of little clinical significance.

The following x-rays and illustrations demonstrate some of the spinal anatomy described:

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Lateral view of the cervical spine

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Lateral view of the cervical spine, C2 pointed for referance

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Anterior-posterior view of the cervical spine; C1, C2, and occiput is visualized on the right

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Lateral view of the cervical-thoracic junction

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Lateral view of middle thoracic spine

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Normal Antaomy of spinal vertebra

The vertebrae come together at three main points: the intervertebral disk between the end plates of the vertebral bodies, and two articular facets. In addition to these three main contact points, the vertebral column is also held together by numerous muscles and their tendinous attachments, and ligaments, which are specialized tissues that connect from one bone to another bone.

Intervertebral disks are composed of two major anatomic zones: the annulus fibrosus and the nucleus pulposus. The annulus is composed of laminated fibrous tissue wrapped around the gelatinous nucleus pulposus. Individual annular fibers radiate outwardly at varying angles to accommodate all the angles of force that can be applied to the disk.

The outer layers of the annulus fibrosus and the dorsal longitudinal ligament contain sensory nerve fibers as opposed to the nucleus pulposus and transitional zone fibers which have none. So called diskogenic pain arises when there is stretching and tearing damage of the outer laminated layers of the annulus fibrosus.

Where vertebrae come together, a "opening" is formed on each side of the spinal column where the spinal nerves and the blood vessels exit and enter the spinal canal. These "openings" are called intervertebral foramina. One nerve exits through each intervertebral foramen. In the canine for example, there are 8 cervical, 13 thoracic, and 7 lumbar spinal nerves that exit these spinal vertebra.

The spinal cord is covered by protective membranes collectively called the meninges. The motor and sensory nerve fibers of each cord segment join inside the meninges to become the spinal nerves before exiting this protective sack as peripheral nerves. The meninges are innervated by numerous sensory nerve fibers called meningeal nerves. When a disk herniates into the spinal canal, the meningeal nerves become compressed and inflamed causing the animal a great deal of pain. In addition, the nerve roots themselves are often compressed, resulting in a great deal of pain for the affected animal and affecting the area that these nerves supply.


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