Intervertebral Disc Disease (Slipped Disk)

Key Points

  • Discs in the mid-back region (thoracolumbar) tend to be under the most stress, thus rupture more commonly, but the discs in the neck can also rupture.
  • The result is pain, weakness, incoordination and, frequently, paralysis.
  • Surgery is often needed to remove ruptured disc material, which is compressing the spinal cord.
  • If your pet has sensation in the hind limbs prior to and after surgery, there is a 90% chance that your pet will regain the ability to walk well again. 

Anatomy

  • The spine is made up of many bones called vertebrae. These are held together by ligaments, muscles and intervertebral discs. The discs act as shock absorbers between the vertebrae.
  • An intervertebral disc consists of a fibrous outer ring and an inner part that is soft and jelly-like (imagine a jelly doughnut) called the nucleus pulposus. The fibrous outer ring is thinner at the top than the bottom.

Disc rupture

  • Discs in the mid-back region (thoracolumbar) tend to be under the most stress, thus rupture more commonly.
  • When a disc becomes diseased, either through premature degeneration, as happens in chondro-dystrophic breeds, or through injury, the thinner top portion of the outer ring tears and disc material displaces into the spinal canal located directly above the disc.
  • When the disc ruptures completely, the outer ring collapses and the inner jelly-like portion is forced into the spinal canal, causing an impact injury.
  • The spinal cord is located in the spinal canal. A bulging or ruptured disc causes irritation, pressure, or damage to the spinal cord. This causes inflammation, which results in irritation, pressure increase or damage to the spinal cord.
  • The resulting inflammation causes back pain, weakness, incoordination and, frequently, paralysis. The damage to the spinal cord impairs the transmission of ‘messages’ down the cables (neurons) in the spinal cord. Thus loss of use of the limbs occurs, as well as little or no control of the bladder and sometimes the bowel. When severe damage to the spinal cord is present, loss of pain sensation to the limbs occurs.
  • The damage to the spinal cord can be temporary or permanent.

Below is a CT scan of a disc rupture in a dog. D is the oval shaped intervertebral disc. Note the white part of the disc which is the diseased (calcified) nucleus pulposus. A fibrous ring surrounds the nucleus pulposus. Also note the large amount of herniated white disc material, labelled with an arrow, that is compressing the spinal cord (yellow) against the top of the spinal canal.

         

Diagnosis

  • A diagnosis of intervertebral disc disease is based on physical signs, neurological tests, and radiography.
  • In order to diagnose where the spinal cord is damaged, a myelogram is usually required. This procedure involves inserting a needle in the space (dural sac) that surrounds the spinal cord and dye (which can be seen on radiographs) is then injected. Radiographs (x-rays) are made to see where the spinal cord is being compressed.
  • In some cases where there is swelling of the spinal cord, a CT or MR scan is also made of the spine, to define clearly the exact location of the disc material. When the surgeon has this information, less manipulation and trauma to the spinal cord may result during the surgery. A CT or MR scan is not needed if the myelogram provides a clear indication of the exact location of the herniated disc material.

Surgery

  • A hemilaminectomy is usually needed to remove ruptured disc material, which is compressing the spinal cord. During the surgery a hole or window is made on the side of the vertebrae at the site of the offending disc. The hemilaminectomy also relieves some pressure from a swollen spinal cord.
  • If the mid-back is being operated upon, fenestration of intervertebral discs in the area may be performed. Fenestration involves making an incision in the side of the disc to allow the jelly portion to leak out. This decreases the risk of a future disc rupture and spinal cord compression.

Prognosis

  • If your pet has sensation in the hind limbs prior to and after surgery, there is a 90% chance that your pet will regain the ability to walk again. After surgery some pets will regain function more quickly than others. At the moment there are no tests to determine how fast a dog will recover.
  • By 3 to 6 weeks after surgery most pets will be able to walk again. Sometimes no improvement in the neurological status is seen in the first month, whereafter improvement can occur. Healing of the spinal cord will continue for a period of 6 months after surgery (at most 9 months). Therefore, by the time 6 to 9 months have elapsed, your pet’s neurological status will be as good as it is going to get.
  • Occasionally some pets will still have some residual weakness in the hind limbs, but will be able to ambulate well enough to be a functional pet.
  • Dogs that have no deep pain sensation in the hind limbs may never walk again. If surgery is done within 12 hours after sensation to the hind limbs is lost, there is about a 50% to 75% chance that the pet will walk again.
  • In the event that your pet does not regain the ability to walk again, a K-9 cart can be fitted to your pet. This device is basically a wheel chair for pets. It has a harness, which is strapped around the pet and wheels to allow the pet to ambulate with the front limbs.

Post-operative care

  • A urinary catheter is often placed if your pet is paralysed and has no voluntary motor function to the hind end, so that the pet will be kept dry and clean.
  • Medications that are given include:
    • Corticosteroids or nonsteroidal anti-inflammatories, to help prevent swelling of the spinal cord and prevent free radical damage to the cord. If used at all they are only given at high doses during the first 24 hours.
    • Side effects of steroids or nonsteroidal anti-inflammatories can include stomach ulceration, rupture of the colon due to ulceration, pancreatitis, increased thirst and urination, increased appetite.
    • Cimetidine, used to treat stomach ulcers if they occur.
    • Antibiotics
      • These are given intravenously during surgery to guard against infection.
      • Antibiotics may also be continued after surgery if a urinary catheter was used, to minimise the possibility of a bladder or kidney infection.
    • Muscle relaxants (valium or methocarbamol)  If your pet has pain due to back spasms after surgery or if you have a difficult time expressing the bladder, a muscle relaxant may be prescribed.

Rehabilitation

  • If your dog cannot walk normally, he should be confined to prevent abrasion injuries that happen when dogs pull their hind legs on abrasive surfaces.
  • Passive rehabilitation: the joints of the hind limb (ankle, knee and hip) should be flexed and extended. Another important exercise is called abduction of the hip. This involves pulling the leg away and toward the belly. These exercises will keep the limbs from becoming permanently stiff. This activity should be done 4 times daily for 10 minutes each time, until your pet can walk again.
  • Active rehabilitation: Your pet’s rear end should be elevated and the hind limbs placed in a standing position. As you balance your pet, allow standing. Early on after surgery your pet will be weak but, with time, he/she should be able to support weight for a longer period of time. This exercise should be done 4 times daily for 5 minutes each time. Another form of rehabilitation therapy is swimming (if a water facility is available). This can be started as soon as 5 days after surgery, and if the pet has some use of the legs. It is best to use warm water. Swimming (with support under the belly) should be allowed 4 times daily for 10 minutes per time.
  • Bladder care. It is very common for patients with spinal injury to have lost control of the bladder and bowels. Your pet should be taken outside 4 to 5 times daily for elimination purposes, so that your pet will be encouraged to perform this bodily function outside. If your pet is not urinating on his/her own, the bladder will need to be expressed (do this outdoors). This is done by applying constant pressure to the belly in front of the hind limbs. Your pet should have a bowel movement within the next 3 days after surgery.
  • Incision. Please check the incision for signs of infection - redness, swelling, pain or discharge. Do not allow your pet to lick at the incision. Please make an appointment to return to your vet 10 to 14 days from the time of surgery for evaluation of the incision, suture removal and neurological status.
  • If your pet is overweight, weight reduction is extremely important since excess weight puts additional strain on the back. Your veterinarian can give advice on how to get your pet to lose weight.

Intervertebral disc disease of the neck

  • Dogs with a disc problem in the neck frequently have pain and sometimes lameness in only one of the front limbs.
  • Some dogs may have paralysis of all four limbs
  • The disc material is usually removed by making a hole in the bottom of the vertebra called a ventral slot.
  • Many dogs will have immediate relief following neck surgery, but occasionally the neck pain may take 1 to 2 weeks to completely resolve.

Notify the doctor if any of the following occur

  • Your pet seems increasingly uncomfortable or there is deteriorating weakness.
  • Your pet stops eating, has vomition or diarrhoea, or has bloody or dark stools.
  • Your pet loses control of its bowel movement or bladder function.
  • Your pet has difficulty urinating or you cannot express the bladder.
  • Your pet has breathing problems, rigid front legs or seizures

Potential complications

Although complications are rare, the following complications have been reported:

  • Infection of the surgical wound and spine
  • Bladder infection
  • Temporary worsening of the neurological status after surgery. This is not uncommon due to the myelogram and the surgical manipulation. If your pet can walk prior to surgery and cannot walk just after surgery, do not be alarmed. The most important factor that indicates whether your pet will recover is retention of good sensation in the hind limbs after surgery.
  • Permanent paralysis. This can occur, but is unusual if deep pain sensation was intact prior to surgery
  • Anaesthetic death
  • Pneumothorax or leakage of air in the chest following fenestration. This can occur but is rare
  • Side effects due to medications (see above).

Dogs that do not regain function of hind limbs

  • Some dogs will not regain the ability to walk again following surgery, in spite of our efforts. Dogs that do not have deep pain sensation prior to surgery have a poorer chance of regaining function.
  • These pets do not need to be euthanised, but require extra attention, which includes the following:
    • exercise
    • expressing urine from bladder
    • urine tests every 2 to 4 months to make sure that bladder infection is not present
    • A K-9 cart, which can be purchased from a company on-line to allow your pet to go for walks again (of course using the front limbs only). In general, pets adjust to the use of a K-9 cart very quickly and enjoy their walks once again. Below is a photo of a dog harnessed to his K-9 cart.
      Please contact us for more information.

        

    

 
   
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