The herniated disc is a degenerative disease of the intervertebral discs and is one of the most common diseases that dogs suffer when showing difficulty moving the hind legs. Compression of the spinal cord occurs when the disc material leaves the spinal canal (extrusion) or bulges (protrusion). This phenomenon usually causes pain and dysfunction in the spinal cord that can be reflected in different degrees; lack of coordination in movement, the dog stops walking, crawling or make costly moves (paresis or paralysis of the limbs), and problems for urination and defecation. To combat the pain, the animal adopts antalgic postures like keeping the head down or arching the dorsal (back) in the area of injury.
It is a condition that can manifest at any intervertebral disc but often this type of injury can be found in cervical spinal segments and thoracolumbar.
The Hansen type I are those corresponding to chondrodystrophoid breeds (small, long spine and short‑legged) such as the poodle, dachshund, Pekingese, cocker, etc., in young animals 2-6 years of age. Chondroid degeneration of the nucleus pulposus occurs with a possible calcification (chondroid metaplasia). The core becomes cartilaginous material, hardens and causes rupture of the disc’s dorsal fibers and the material leaving the spinal canal (extrusion into the spinal canal) providing a sharp focal compression. It is produced by abrupt movements in the column such as jumps, falls, hits or going up and down the sofa. The compression is acute although the problem may be due to an acute cause or an evolution of micro-traumas.
The disc degeneration Hansen type II corresponds to large breeds that are nonchondrodystrophoid such as Boxers, Labradors, German Shepherds, Rottweilers, etc., in adult animals from 5 to 12 years old. Evolution of this type is slow throughout the dog’s life and problems show up later. A gradual protrusion of the annulus fibrosus of the intervertebral disc content that has degenerated over time (fibrous metaplasia) is generated. The material is intact; a focal, slow and progressive compression occurs (myelopathy).
It is possible that noncondrodystrophoid breeds get Hansen type I disc degeneration at any age.
There is a third classification, disc degeneration Hansen type III. They are acute, severe extrusion followed with progressive myelomalacia generating in many cases the death of the animal.
Pain, the animal adopts antalgic postures due to inflammatory reactions (lowers the head and curves the back).
Decreased proprioception, the animal leaves a paw, is unable to properly put the pad in contact with the ground lacking coordination in his movements, and makes harsh movements or crawls (paresis or paralysis), difficulty maintaining balance.
A loss of sensitivity occurs in the injured area and extremities.
Problems with urinary incontinence and/or fecal or retentions.
Within a few days an alteration of the muscle tone occurs along with decrease in mass and strength.
For the diagnosis of herniated discs, the veterinarian needs to know the history, race, age, any clinical signs the animal presents and will perform a neurological examination.
A radiograph of the spine will show whether there is decreased intervertebral space, but it is not possible to know how the intervertebral are unless first calcifying the discs, therefore, it is difficult to see the herniated material. In such cases, a myelogram is generally performed.
Myelography is a technique that allows, through the introduction of iodinated contrast around the spine (subarachnoid area), to see the outline of it. By glancing at it, one can see where there is compression.
There are other complementary methods such as CT (Computed Tomography) and Nuclear Magnetic Resonance with which you can also diagnose the exact point where the hernia has occurred.