Atlanto-axiale instability

This condition also known as antlanto-axial dislocation or malformation, is an instability of the joint between the first two cervical vertebrae (atlas and axis). It results in a compression of the spinal cord at this level, with pain and varying degrees of neurological impairment.

The instability is caused by a malformation of the axis (second cervical vertebrae) and/or a lack of support of the ligaments connecting the two vertebrae to each other. It is possible that a minor trauma caused the dislocation of the vertebrae and this precipitated the onset of clinical signs of the condition.

A congenital malformation is often the cause in small breed dogs such as, Miniature or Toy Poodles, Pomeranians, Yorkshire Terriers, Chihuahuas and Pekingese. These dogs are usually less than 2 years old at initial diagnosis. It is rarely found among large breed dogs and cats.

Clinical signs


The clinical signs most commonly observed are:

Cervical pain
Head held low
Ataxia (crooked gait)
Tetraparesis (weakness of all 4 limbs) light to moderate and progressive.
With a severe compression of the spinal cord, rarely will the condition evolve towards paralysis causing respiratory paralysis and death.

Upon examination, we can observe neurological deficiencies suggestive of a lesion in the spinal cord between CI and C5 (cervical region) as well as, pain in this region.

Treatment

The goals of treatment are to stabilize the affected joint, improve the neurological condition or avoid having it become worse, thereby removing the pain.

First of all, the animal must be restrained in a cage. In order to stabilize the cervical region, a padded bandage should be placed and it goes without saying, that collars must be avoided! During an acute phase, an anti-inflammatory medication will be prescribed.

For long-term treatment, surgery is the method of choice in order to permanently stabilize the involved joint. In certain, less severe cases, a brace including a restrained degree of activity may be palliative but, is not the method of choice. However, the neck muscles will atrophy (become weak) and this will increase the risks of trauma when the brace is removed.

Prognosis

With medical treatment, prognosis is reserved since there is no definitive correction of the instability and there will be recurrences.

The success of the surgery depends of the animal’s age, when clinical signs appeared, of the duration, as well as, the degree of neurological impairment before surgery.

If the animal was younger than 24 months of age when clinical signs appeared, if the signs were present for less than 10 months and if there is no or very little neurological impairment (normal gait or light ataxia) , the better the prognosis.

The success rate of the surgical treatment is around 70-75%.

Affected animals should not reproduce as to avoid transmitting the condition to its offspring.

 

Références :

Côté, Étienne, Clinical veterinary advisor Dogs and Cats, Mosby, Missouri, 2007, pp.93-94.
Nelson, Richard W. and C. Guillermo Couto, Small Animal Internal Medicine, 3rd ed., Mosby, Missouri, 2003, pp. 1046-1047.