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Sagittal - R Lateral Recess

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1. Multifidus muscles: one of the largest epaxial muscle groups in the lumbar region. Divided into 11 individual portions that orginiate from the articular processes of the sacrum and mammillary processes of T12-L7. Can appear atrophied in dogs with chronic degenerative spinal disease or degenerative myelopathy.

2. Articular process joint: Paired, synovial joints dorsal to the vertebral canal. Formed by the cranial and caudal articular processes of contiguous vertebrae. Osteoarthritis of the articular process joints can contribute to nerve root compression in dogs with degenerative lumbosacral disease.

3. Articular process: Synonym: facet. Interdigitating bony prominences that form the articular process joints between adjacent vertebrae. In the lumbar spine, these form the dorsal boundaries of the intervertebral foramina. In dogs that have nerve root compression within the intervertebral foramen, portions of the articular processes often have to be removed.

4. L5 caudal articular process

5. Interlaminar space: Synonym: interarcuate space. Space between laminae of adjacent vertebrae. Occupied by the yellow (interarcuate) ligament and medial portions of the articular process joint capsules. In dogs with degenerative lumbosacral disease, the L7-S1 interlaminar space is often narrowed. This is associated with buckling and hypertrophy of the ligaments.

6. Lamina: forms the dorsal boundary of the vertebral canal. Has small notches on the cranial and caudal margins that form the boundaries of the interlaminar spaces and serve as the attachment sites for the yellow (interarcuate) ligaments. In dogs with idiopathic stenosis, the laminae may appear thickened and sclerotic.

7. Epidural fat: fat deposits are normally present in the epidural space and appear darker than surrounding nerve tissues on CT images. These fat deposits help provide cushioning and protection of the nerve tissues. In dogs with degenerative lumbosacral disease, loss of visualization of the epidural fat is a sign of nerve tissue compression.

8. Ca1 cranial articular process

9. Ca3 articular process

10. Ventral longitudinal ligament

11. Intervertebral disc: Cartilaginous joint between endplates of adjacent vertebrae. Consists of concentric bands of fibrous tissue (annulus fibrosus) surrounding a central gelatinous portion (nucleus pulposus). Type II disc degeneration is one of the most common causes of nerve root compression in dogs with degenerative lumbosacral disease. With type II disc degeneration, the annulus bulges outwardly in all directions and bone spurs form on the vertebral endplates at the attachment sites for the annulus.

12. Cauda equina: structure composed of the paired, L5-Caudal nerve roots that arise from the terminal portion of the spinal cord. Named for the appearance that resembles a horse’s tail. Most commonly occupies the L5-S3 vertebral canal. In dogs with degenerative lumbosacral disease, compression of the cauda equina nerve roots or their blood supply is the most common cause of clinical signs.

13. Body of sacrum: formed by the fusion of the S1-3 vertebral bodies. Ventral subluxation of the sacrum can contribute to compression of nerve roots in dogs with degenerative lumbosacral disease.

14. Sacrocaudalis ventralis lateralis

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