Intervertebral Disc Disease – Slipped Disc


Key Points

Discs in the mid back region (thoracolumbar) tend to be under the most stress thus rupture more commonly

The result is weakness, incoordination, and frequently paralysis

A hemilaminectomy is usually 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 gradual degeneration or 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.
  • 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, 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 and little or no control of the bladder and sometimes the bowel occurs. When severe damage to the spinal cord is present, loss of pain sensation to the limbs occurs.
  • 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 labeled 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 usually is required. This procedure involves inserting a needle in the bag (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 most cases a CT scan is also made of the spine to clearly define 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 scan may not be 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 off of a swollen spinal cord.
  • If the mid-back is being operated, fenestration of intervertebral discs in the area is frequently 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 in the future.

 

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 well again. After surgery some pets will regain function quicker than others.
  • 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, then a rapid improvement occurs. 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 lapsed, 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 to 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 basically is 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.

 

Postoperative care

  • A urinary catheter is usually placed if your pet is paralyzed and has no voluntary motor function to the hind end so that the pet will be kept dry and clean.
  • Medications are given include:
    • Steroids: 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:  Stomach ulcers, rupture of the colon due to ulceration, pancreatitis, increased thirst and urination, increased appetite
    • Pepcid and carafate and misoprostol
      • These are used to treat stomach ulcers if they occur
    • Antibiotics
      • These are given intravenously during surgery to prevent against infection.
      • Antibiotics may also be continued after surgery if a urinary catheter was used after surgery to minimize 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.
  • Rest: Your pet should be kept in a crate at all times except for urination and bowel movements for a period of one month.
  • 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 getting 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 back 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 about 7 days after surgery (at this time the incision will be sealed). Best is 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 do 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 with in the next 3 days.
  • 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 MVS in 10 to 14 days from the time of surgery for evaluation of the incision (usually no external sutures to be removed) and neurological status.
  • If your pet is overweight, weight reduction is needed since excess weight puts additional strain on the back.
  • Provide a soft padded bed to prevent bedsores. These are sometimes seen on the points of the buttocks if the pet is constantly sitting up on its hind end. Any of the bony parts of the limbs can develop bed sores from laying on that part of the body too long and failing to turn the body.

 

Notify the doctor if any of the following occur

  • Your pet seems increasingly uncomfortable
  • Your pet loses control of its bowel movement, is constipated, or has bloody or dark stools
  • Your pet has difficulty urinating or you cannot express the bladder
  • Your pet has breathing problems, rigid front legs or seizures.

 

Intervertebral disc disease of the neck

  • Dogs having a disc problem in the neck frequently only have pain and sometimes lameness of 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

 

Potential complications

  • Infection of the spine
  • Bladder infection
  • Temporary worsening of the neurological status after surgery is not uncommon due to the myelogram and the surgical manipulation. If your pet can walk prior to surgery and cannot just after surgery, do not be alarmed. The most important factor that indicates whether your pet will recover again is retention of good sensation to the hind limbs after surgery.
  • Permanent paralysis can occur, but is unusual if deep pain sensation was intact prior to surgery
  • Anesthetic death
  • Life threatening pneumothorax or leakage of air in the chest following fenestration 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 a poorer chance to regain function.
  • These pets do not need to be euthanized, 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 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.

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