What does it mean for a disc to rupture, and how does it happen?

The disc is composed of two parts. The outer covering, comprised of tough fibers, is much like a thick shell and contains the central part. The disc is thinnest at the top. This thin area is located just below the spinal cord. The central part of the disc is much softer than the outer part and has the consistency of thick toothpaste.

When the outer shell degenerates, it allows the central part of the disc to escape. This is called a disc rupture or a "slipped" disc. Since the disc is thinnest near the spinal cord, disc material that escapes through the tear usually goes upward, putting pressure on the spinal cord. Because the spinal cord is encased within its bony canal, it cannot move away from the pressure and it becomes “pinched”.

Degenerative disc disease causes spontaneous degeneration of the outer part of the disc, resulting in disc rupture. It may not be related to injury, although trauma is a common cause. It is also not related to age. Most dogs with degenerative disc disease are 3-7 years old. It is a sudden event most likely due to genetic factors. Certain breeds, especially the Dachshund, Poodle, Pekinese, Lhaso Apso, German Shepherd, Doberman and Cocker Spaniel have a high incidence of disc disease.

Most owners report that a disc rupture occurred following some kind of traumatic event, such as a relatively small jump or fall. Although this act is frequently blamed for the disc rupture, the injury actually occurred due to chronic disc degeneration.

How does a slipped disc affect the spinal cord?

The spinal cord is like a telephone cable carrying thousands of tiny wires. When it is crushed, transmission of information through the wires is slowed or stopped. When the disc degenerates and ruptures, pressure on the spinal cord results in pain and/or loss of information transmission causing partial or complete paralysis.

Most disc ruptures occur in the middle to lower part of the back. However, they may also occur in the neck.

How fast do discs degenerate and rupture?

Disc degeneration usually occurs relatively slowly, usually over several days or weeks. However, discs may also rupture very acutely. Some dogs will go from normal walking to total paralysis in less than one hour.

How is a slipped disc diagnosed?

A presumptive diagnosis of disc disease is made based on the dog's history and physical examination. In some cases, plain radiographs (x-rays) are necessary to assist in the diagnosis, but they may also be normal since neither the disc nor the spinal cord is visible on an x-ray. If the diagnosis is in doubt or if surgery is to be performed, a myelogram or MRI  may be done.

How do you know if the pressure on the spinal cord is due to a disc or something else?

It is possible that the pressure is due to a blood clot or tumor. Both are possible but rare, especially when compared to disc ruptures. If the patient is a high-risk breed and there has been a sudden onset without trauma, there is an approximately 95% chance that a disc rupture is causing the clinical signs. However, the diagnosis is not definite until the time of surgery.

Are all disc ruptures treated with surgery?

Not necessarily. Treatment is based on the stage of the disease. These stages tend to overlap in some dogs, and dogs may move from one stage to another over a period of hours to days. Patients are usually treated with anti-inflammatory drugs, pain relievers, and restriction from exercise. Surgery may also need to be considered. The sooner that surgery is done, the better the prognosis. Ideally, these dogs should be operated on within the first 24 hours of the onset of paralysis.

What is the purpose of surgery?

The goal of surgery is to remove pressure from the spinal cord.

What is the success rate for treating disc disease with and without surgery?

When will we know if the surgery is successful?

Unfortunately, success cannot be determined immediately. The return of neurological function, walking ability and relief from pain may not occur for several days to weeks after surgery.

 Can my dog slip a disc again?

The answer is "yes". However, more than 95% of degenerated discs will heal without surgery. So the chance of your dog requiring a second surgery is less than 5%.

What if the myelogram is normal?

The purpose of the myelogram is to identify pressure on the spinal cord. If the myelogram is normal, there is no pressure on the spinal cord. This has several important implications. First, it means that surgery will generally not be appropriate. Second, it means that one of the following conditions is likely to exist: spinal shock, fibrocartilaginous embolism, or degenerative myelopathy.

A normal myelogram in a dog with slowly progressive paralysis is very frustrating because the two most likely diseases, Fibrocartilaginous

Embolism and Degenerative Myelopathy, cannot be confirmed without an autopsy.

Cindy McCauley-Atkinson, DVM