What is it?The spine of a dog is a bony column of vertebrae that protects the spinal cord. The spinal cord sends messages between the brain and the muscles to coordinate movement. The vertebrae have round cartilage pads (called intervertebral discs) between them which act as shock absorbers. Spinal injury has a number of different causes. The most common is intervertebral disc disease (IVDD).
How many kinds of intervertebral disc disease are there?IVDD has two main categories, Hansen Type I and Hansen Type II.
What is Hansen Type I ?This type of disc disease begins earlier in life and is usually seen in dogs between 2-7 years of age. Early degeneration of the discs causes a loss of the shock absorber effect and instead of having a spongy texture, the core of the disc becomes hard. Under pressure from movement, the core of the disc suddenly explodes through the membrane above it into the spinal cord. The amount of damage to the spinal cord depends on the speed of the disc fragment, rather than the size of the fragment.
What is Hansen Type II?This type of disc disease generally occurs in older, large breed dogs. Age related hardening of the discs and weakening of the protective membrane leads to the disc bulging into the spinal cord, causing compression.
Are there any other causes of spinal injury?
Why is it important?
What is the risk?
What happens to the dog?
How does the vet know what is going on?Your vet will ask for information on when the problem started, and if there has been any history of trauma such as a road traffic accident. The animal is examined and will often have pain on careful manipulation of the spine. If the animal is paralysed, the toes are pinched firmly to assess for ‘deep pain’. Normally the animal should move the limb away when the toes are pinched. When a spinal cord compression occurs, the nerve fibres at the centre of the spinal cord that sense ‘deep pain’ are the last to be damaged. If the patient cannot feel and respond to a firm pinch of the toes by moving the limb away, this indicates that they have ‘no deep pain’ and referral for MRI scanning and surgery are potentially indicated. X rays are not very helpful for diagnosing IVDD although they can suggest a narrowing of disc spaces. MRI scanning is the gold standard as it shows far more detail of the spinal cord itself, and the extent of the spinal cord damage.
What can be done?
Type I disease - A dog who has spinal pain with no paralysis can be managed with strict cage rest and pain relief for at least 2-4 weeks.
If the dog is off their legs altogether because of disc disease, surgery is urgently needed (ideally within 48 hours) to decompress the spinal cord and remove the disc fragment. 80-90% of dogs who can sense deep pain at the time of surgery will walk again after surgery.
If the dog has no deep pain response, then getting them to surgery within 12 hours improves the outlook. If the deep pain response has been gone for more than 48 hours, there is a less than 5% chance of the patient walking again.
If the deep pain response does not return within 2-4 weeks after surgery, then the prognosis is poor.
For Type II disease, the surgery is more difficult as there is often a wider part of the spinal cord that is damaged. A dog who has spinal pain with no paralysis can be managed with at least 4 weeks cage rest and pain relief. 22-52% of cases will recover.
Chronic compression causes death of parts of the spinal cord. This cannot be reversed, and carries a poor prognosis.
For other types of spinal injury, it will depend on how the spine has been damaged, and how much damage there is. For example, spinal fractures where the spinal cord is bruised, but not cut, may be able to heal if the fracture is rapidly repaired with pins or plates. If the cord is too badly damaged though, it may not be possible, and sadly in many cases euthanasia is the only kind option.