The spine is composed of many small bones called vertebrae, which are held together by muscles
and ligaments. In between each vertebra lies an intervertebral disk, which acts as a shock absorber to
disperse physical forces placed on the spine. They also serve to cushion the bones of the spine, allowing
for flexibility without discomfort. Each intervertebral disk consists of an outer fibrous ring, called the
annulus fibrosis, and in inner core that is soft and gelatinous, called the nucleus pulposus. Directly above
the intervertebral disk sits the spinal canal, in which the spinal cord is located. (show vertebral anatomy)
Damage to an intervertebral disk can cause the outer fibrous layer to rupture, which forces the nucleus
pulposus into the spinal canal. The extruded disc material causes irritation to the spinal cord, which
results in inflammation in the area. The inflammation leads to more irritation, pressure, and damage to
the fragile spinal cord. Damage to the spinal cord prevents nerve transmission from the brain down to
the organs and muscles it innervates, and results in the loss of function of the limbs and loss of bladder
and bowel control. Severe damage to the spinal cord causes the loss of pain sensation in the limbs as
Intervertebral disk disease is the most common surgical neurologic disorder diagnosed in veterinary
patients. It typically affects dogs that are young or middle aged. While IVDD can occur in any breed of
dog, it is often seen in breeds that have long backs, and short legs, such as Dachshunds, Corgis, and
Basset Hounds. Dachshunds are by far the most common breed diagnosed with intervertebral disk
Intervertebral disk disease can affect any segment of the spine, from the neck to the end of the tail.
Most commonly however, it is seen in the thoracolumbar (lower back) and the cervical (neck) regions.
Clinical signs will depend on the part of the spinal cord that is damaged, as well as the extent of the
damage. Severity of IVDD can range from extra pressure on the disk causing a bulging of the disk
material (the nucleus pulposus), to a complete rupture of the disk material. It can also involve just
one or several intervertebral disks. Clinical signs usually begin with a stiff, stilted gait, and reluctance
to move the head or neck. Dogs with cervical disk disease may carry their heads lower than normal.
Muscles spasms of the neck and shoulder are also common. In milder cases, the only signs of IVDD are
back or neck pain. Severely affected dogs can have paralysis, loss of sensation, and lack of bladder and
bowel control. Approximately 10% of affected patients are tetraparetic, meaning they show muscle
weakness of all four limbs.
A diagnosis of intervertebral disk disease is made based on clinical signs, neurological test, and
radiography. Traditional radiography is usually not sufficient for discerning where the spinal cord is
damaged. Therefore, a myelogram is usually performed. This involves inserting a needle in the space
that surrounds the spinal cord, called the dural sac, and injecting dye into the space. X-rays are then
taken, and the dye elucidates the area of spinal cord damage. CT scans and MRIs are diagnostic tools
that are also used to identify the exact location of the ruptured disk. (show myelogram for IVDD
In some cases, IVDD is a result of degeneration of the intervertebral disks. Degenerative changes occur
in the nucleus pulposus, and the disk loses its ability to absorb shock. Continued deterioration causes
the disk material to protrude; rupture of the disk occur spontaneously or can be secondary to trauma
to the already weakened intervertebral disks. This form of IVDD is characterized by an acute, massive
extrusion of the disk material into the vertebral canal. In other cases, IVDD occurs from degeneration of
the fibrous ring, the annulus fibrosis. This type of intervertebral disk disease is characterized by a slow,
chronic protusion of the annulus fibrosus into the vertebral canal.
Animals that are mildly affected may be candidates for medical treatment. This includes confinement
and exercise restriction for a period of 4-6 weeks, in combination with non-steroidal anti-inflammatories
(NSAIDs) to attempt to reduce some of the inflammation of the spinal cord. Corticosteroids may be
used in place of NSAIDs. Dogs with more severe cases of IVDD may require surgery to remove the
extruded disk material and relieve pressure on the spinal cord. One surgical procedure used is called
a laminectomy or hemilaminectomy. A hole or window is made on the side of the vertebra where
the ruptured disk is located. Removing a window of bone allows for removal of the disk material
and decompression of the spinal cord. Depending on the part of the spine that is being operated on,
fenestration of intervertebral discs is another surgical technique. Fenestration involves making an
incision in the side of the disc to allow the ruptured disk material to leak out. This decreases the risk of a
future disc rupture and spinal cord compression in the future.
Prognosis depends greatly on the condition of the animal prior to treatment. Dog that have sensation
in the hind limbs prior to and after surgery have a 90% chance of regaining the ability to walk well.
Improvements are usually seen by 3-6 weeks post-op. Healing of the spinal cord takes about 6 months,
so by 6-9 months, the patient will have recovered as much as it can, and the neurological status is as
good as it will get. Some patients continue to have weakness in the hind end and may still be wobbly,
but otherwise function as normal pets. Dogs that lose their ability to feel pain in their limbs have a poor
prognosis for regaining the ability to walk. The greatest chance for recovery in these dogs is if surgery is
performed within 12 hours of losing sensation to the hind limbs. If this is done, there is about a 50-75%
chance that the dog will be able to walk again. It is also important to note that dogs that do not regain
function of the hind limbs need special attention in that they may need to have urine expressed from
their bladder manually, since control over the bladder will likely not return either. They also need to be
monitored for urinary tract infections. Even if your dog does not regain use of the hind legs, there is still
the option of having your dog fitted for a wheelchair. Many dogs adapt well to using a wheelchair.