Dogs, like their human masters, often suffer from disease processes that are caused by abnormalities of the spinal discs. The severity of the condition varies from stiffness and difficulty in getting up after resting to complete paralysis.
The spinal disc is a flattened structure that separates each bone in the animal’s vertebral column. The outer, thinner portion of the disc consists of lough fibrous material surrounding a thicker, pulpy nucleus. The function of the disc is to support the vertebrae and to maintain the relative position of the two vertebrae to which it is attached throughout the many complex strains and torsions associated with normal movement.
The thicker pulpy area containing the nucleus is most important in absorbing shocks and thus limiting the jarring of the spinal cord during vigorous running and jumping.
As the animal ages, the composition of the spinal disc changes. The fibrous areas surrounding the nucleus become less elastic and may rupture if subjected to unusual torsion. The nucleus becomes rigid and loses some of its shock-absorbing properties. In this less flexible state, sudden shocks may displace it, pushing it through the fibrous rings covering it, and allow it to impinge upon the spinal cord, running in its canal immediately above.
It is the pressure effect of the displaced rigid nucleus of the disc upon the nerve elements of the spinal cord that produces the varying degrees of loss of nervous function seen in spinal disc lesions.
In cases where the displacement of the nucleus has not been too great, or has not occurred too violently, the dog may exhibit only mild discomfort when first getting up or when attempting to jump or turn quickly. With rest, the damage to the spinal cord subsides and the symptoms gradually disappear.
More serious displacement of the nucleus of the disc causes greater amounts of compression of the nervous pathways within the cord. The dog may appear weak in the back legs, may have difficulty in standing, and maybe particularly sensitive to handling over the mid-back area. The abdominal muscles are very tense, and the dog is in obvious discomfort.
Major displacement of the damaged elements of one or more intervertebral discs may cause such severe compression and damage to the nerve pathways of the spinal cord that complete paralysis occurs. The dog has no control over its hind limbs and the normal functioning of its bladder and larger bowel may be impaired.
While degeneration of the cells making up the intervertebral disc increases with age in all breeds, in certain breeds these changes are more marked and begin at an early age. Dogs with long backs and shortened legs, such as dachshunds, corgis and basset hounds, are most likely to develop spinal disc lesions. Of the other dogs, heavy breeds such as labradors and German shepherds seem most prone.
Dogs that are overweight and under-exercised are more likely to suffer spinal disc protrusions. Animals that frequently jump onto chairs or have to negotiate long flights of stairs or are encouraged to stand upon their hind legs are all more likely to develop spinal disc lesions. Activities that produce sudden torsions of the spine such as sliding and turning while chasing a ball or stick, can trigger a disc prolapse even in the young, fit animal.
The treatment of spinal disc disease varies with the symptoms and the degree of the protrusion. Much can be achieved with appropriate therapy and patience, even in severely affected animals.