What are the characteristics of the intercapital ligament?
-seen from T1 to T10
-connects the two rib bones at each vertebrae
-provides support and limits disc dz in this region
What are the general characteristics of disc degeneration?
-discs are supposed to be soft and flexible to allow for motion and absorb stress
-if discs become less flexible, stress can be more focused and cause greater wear and tear in one area
-most discs extrude because they first degenerate
What are the characteristics of cartilaginous degeneration?
-aka Hansen type 1
-seen in chondrodystrophic breeds
-acute extrusion
-caused by an extra copy of fibroblast growth factor 4 gene
-disc is replaced with cartilage that can later calcify
What are the characteristics of fibrous degeneration?
-aka Hansen type 2
-seen in older, large breed dogs
-chronic protrusion
-aging degeneration of disc causes disc to dry out and be replaced with fibrous tissue
What are the possible changes that can occur at the level of the spinal cord?
-mechanical/compression of cord
-ischemia
-edema
-hemorrhage
-free radical damage
What determines the severity of neurological deficits in disc disease?
-volume of disc material
-rate of extrusion
-duration of compression
What are the characteristics of acute, compressive extrusions?
-seen in chondrodystrophic breeds
-3 to 6 years old
-acute onset
-linked to genetic mutation
What are the characteristics of chronic protrusions?
-large breed dogs
-older than 6 years old
-chronic onset
What are the characteristics of acute non-compressive nucleus pulposus extrusion?
-normal, non-degenerated disc
-annulus tears without previous degeneration
-nucleus pulposus violently strikes cord to cause contusion
-does not cause persistent compression of cord
-surgery will not help these cases
Which discs most commonly experience extrusion in the thoracolumbar region?
-T12 to T13
-T13 to L1
Which disc most commonly experiences extrusion in the cervical region?
C2 to C3
What are the clinical signs seen in disc disease cases, from least to most severe?
-pain
-ambulatory paresis
-non-ambulatory paresis
-paralysis
-paralysis with loss of deep pain
-ascending-descending myelomalacia
What are the clinical signs seen in patients with thoracolumbar disc extrusion?
-back pain (nerve root stretched or compressed)
-hump back posture
-tense abdomen
-reluctant to get up on back legs or move around
-back legs affected while front legs normal
-intact spinal reflexes
What are the clinical signs seen in patients with cervical disc extrusion?
-neck pain
-thoracic limb lameness/root signature; pain down into legs due to spinal lesion
-tetraparesis or tetraplegia
-respiratory weakness
Why are radiographs not the imaging modality of choice for disc disease?
-they are not very sensitive or specific for disc extrusion
-lesions on plain films may not be consistent with clinical findings
-not enough information for surgical planning
What are these arrows identifying in this radiograph (clockwise from the top)?
top: spinous process
next: articular facets
middle: intervertebral foramen
next: disc space
bottom: transverse process
What are the abnormalities shown in this radiograph?
-articular joint space is closer together
-vertebrae are closer together (smaller disc space)
-intervertebral foramen is smaller
What is the abnormality shown in this radiograph?
calcified disc material in the intervertebral foramen
What are the abnormalities shown in this radiograph?
left arrow: narrowed disc space between C2 and C3
right arrow: calcified disc between C6 and C7
What are the characteristics of myelography?
-injection of contrast material into subarachnoid space
-highlights extradural compression dorsal to disc space
-not common anymore; irritating to spinal cord and can cause seizures
What is shown in these images?
left: normal CT
right: calcified disc material in vertebral foramen
What is shown in this image?
MRI identifying disc protrusion/displacement of spinal cord
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