Dog - Degenerative Disc Disease

What is an intervertebral disc and what is its purpose?

The spinal cord is one of the most important and most sensitive organs in the body. If it is damaged the nerve cells do not regenerate but are replaced with scar (fibrous) tissue resulting in permanent loss of function. The spinal cord is therefore well protected. It occupies a spinal canal within the vertebrae (back bones) entirely surrounded by bone except over the intervertebral discs.

These are fibrous cushions between the vertebrae. They allow a range of movement between the individual vertebrae of the spinal canal (so you can bend your back).

What is a ruptured disc?

The intervertebral disc is composed of two parts. The fibrous outer covering is protective, similar to a shell. It is thinnest at the top just beneath the spinal cord. The inner, central part of the disc is composed of semi-solid material which acts as a shock absorber. If the outer shell degenerates and weakens the central part of the disc can escape. This is disc rupture or ‘slipped’ disc. Since the 'shell' is thinnest nearest to the spinal cord, this is commonly the area from which the gel-like central disc material will escape resulting in pressure on the nervous tissue of the spinal cord which leaks causing pressure on the nervous tissue of the spinal cord. Within the bony spinal canal there is not sufficient room for the spinal cord to move away from this area of pressure.

Degenerative disc disease resulting in weakening of the outer part of the disc does not appear to be related to injury or age. It can affect dogs between 3 and 7 years of age and is most likely controlled by genetic factors. Breeds including Dachshund, Poodle, Pekinese, Lhaso Apso and Cocker Spaniel have a high incidence of disc disease whereas others, such as the German Shepherd and Doberman have a much lower incidence. Many breeds never appear to encounter these problems.

Many owners report that the disc rupture occurred following trauma such as a relatively small jump or fall. This is frequently blamed for the problem but it is unlikely that it would have occurred had not the disc already been weakened.

How does a slipped disc affect the spinal cord?

Imagine the spinal cord as a telephone cable carrying thousands of individual wires. When it is damaged transmission of information through the wires is stopped. This is similar to disc degeneration and rupture causing pressure from the pulpy central material on the spinal cord and the spinal nerves that leave the cord over the discs. Spinal nerves leave the spinal cord at roughly each vertebrae to provide nervous function to the local tissues. A bit like an electrical cable feeding off of the mains into your house, then another one feeding from the mains into next door's house (the mains being the cord, the cable to each house being the spinal nerves)

Pressure on the spinal nerves results in pain whereas pressure on the spinal cord results in pain and/or loss of transmission resulting in paralysis.

Where along the spine does this usually occur?

1. Neck. This can result in paralysis of all four limbs. However due to the arrangement of the nerve tracts, cervical (neck) disc ruptures may affect the rear legs first or even exclusively.
2. Middle and lower (posterior) back. In this site there is often severe pain sometimes without paralysis.

Does disc degeneration occur rapidly?

Disc degeneration usually occurs relatively slowly, i.e. over several days or weeks. Pain and reluctance to move are usually the first signs and sometimes this enforced rest resolves the problem. Disc protrusion can also occur very rapidly resulting in paralysis in less than an hour.

How is a slipped disc diagnosed?

Initial diagnosis is based on history of neck or back pain, uncoordinated movement or paralysis with no history of injury. Physical examination will indicate a spinal source, indicating possible disc disease. If the dog is one of the breeds with high incidence this is further evidence.

Plain x-rays (radiographs) may assist but neither the disc nor the spinal cord are visible on x-ray. A technique known as myelography usually has to be undertaken. Under anaesthetic a dye visible on x-rays is injected around the spinal cord. Subsequent radiography will reveal this dye. If there is a break in the dye column this means that there is pressure on the spinal cord at that site.

How do you know that the problem is due to pressure from a ruptured disc?

Spinal pressure could be due to a blood clot or a tumour. These are not common compared with disc ruptures. If the patient is from a prone breed, there has been sudden onset, and no history of trauma, the likelihood is about 95% that the problem is due to disc rupture. Diagnosis is not definite until surgery reveals the cause.

Are all disc ruptures treated with surgery?

Treatment depends on several factors: the severity of the disease, the amount of pain or paralysis involved, whether the dog is ambulatory (able to walk), has control of bladder and bowel function etc. Some cases showing only mild pain, for example, will be treated with analgesics (pain killers) and rest and are usually self correcting in a few days. At the other end of the scale there are cases of sudden onset resulting in total loss of sensation and paralysis for which immediate, emergency surgery is imperative.

Each case has to be assessed individually and the treatment plan formulated once all the diagnostic work-up has been completed. Over all however we can say that those cases treated surgically have an increased likelihood of making a better and more rapid recovery.

What does surgery involve?

The aim is to remove pressure from the spinal cord. This is achieved by entering the spinal canal usually through the vertebra wall or sometimes via the intervertebral disc itself, depending on the site of the pressure.

When will we know if the surgery is successful?

This depends on several variables, particularly the severity of the condition and how long it has been present before surgery. Sometimes ambulation (walking) and relief from pain does not occur for several days or even weeks.

Is there a lot of nursing or hospitalisation post operatively?

This depends on the individual circumstances and will be discussed with you fully. If paralysis of the bladder and/or bowel was present pre-surgically we try to ensure that control is returned before the dog goes home. It is also important that during the recovery period exercise is strictly controlled and this we will discuss with you particularly with respect to confinement of the dog. Over-activity during recovery can be very deleterious.

If you can carry out basic nursing care, which we will discuss, hospitalisation will only be a few days.

If you do have any concerns about aftercare, please feel free to discuss them with us.

Is it possible for the condition to recur once recovered from the surgery?

In breeds prone to the condition there is always the possibility that another disc may rupture but this is relatively rare.