Surgical Considerations of Thoracolumbar Intervertebral Disk Disease

Pathogenesis Hoerlein determined that intervertebral disc disease (IVDD) accounted for 2.02% of all diseases diagnosed in dogs (Hoerlein 1952). Incidence of IVDD peaks at 4 to 6 years of age in chondrodystrophic breeds and at 6 to 8 years in nonchondrodystrophic breeds (Priester 1976). The Dachshund had the highest frequency followed in succession by the Pekingese, Welsh corgi, Beagle, Lhasa Apso and miniature poodle (Hoerlein 1952). Hansen first classified IVDD as type I and type II (Hansen 1951). Hansen type I is herniation of the nucleus pulposus through the annular fibers and extrusion of nuclear material into the spinal canal. Hansen type I IVDD is typically associated with chondroid disc degeneration and has an acute onset. The disc extrudes through the dorsal annulus, causing dorsal, dorsolateral or circumferential compression of the spinal cord. Acute disc extrusion is characterized by the presence of soft disc material within the vertebral canal and extradural hemorrhage. Chronic disc extrusion is characterized by extradural fibrous adhesions around the herniated disc material that has often become a hard mineralized mass. The thoracolumbar junction (T12-13 to L1-2) accounted for the highest incidence of all disc lesions (Hoerlein 1987). Large nonchondrodystrophic breeds of dog such as the Doberman pinscher and Labrador retriever may also be affected with Hansen type I IVDD (Cudia 1997). The most common site in large breed dogs is the interspace between L1 and L2 (Cudia 1997).