Atlantoaxial instability is a condition in which the first two cervical (neck) vertebrae are not firmly attached. Normally, the atlas (the first cervical vertebra) and the axis (the second cervical vertebra) are attached by a group of ligaments. They are further stabilized by a prominence on the axis called the dens that protrudes into a hole in the atlas.
Dogs with congenital atlantoaxial instability are born without ligament support to their atlantoaxial joint, and may also be born without a dens. Trauma to the neck can also cause tearing of the ligaments or fracture of the dens, resulting in atlantoaxial instability.
Atlantoaxial instability can lead to cervical spinal cord injury, the symptoms of which include: neck pain; a drunken, staggering gait; paralysis of all four legs; or sudden death.
Causes
Breeds at risk for congenital atlantoaxial instability include all toy breeds, especially Chihuahuas, Pomeranians, Pekingese, toy poodles, and Yorkshire terriers. These dogs usually show signs at less than one year of age, and symptoms can occur after very mild trauma, such as jumping off furniture, which would be considered normal activity.
Any dog, young or old and of any breed, is at risk for atlantoaxial instability after a traumatic event, such as being hit by a car or being an unrestrained passenger in a car accident.
Diagnosis
Your veterinarian will ask you many questions to develop a complete history of the progression of the problem. These questions will include: what is your pet's age, was there any traumatic event, what symptoms have you noticed, how long have they been going on, what treatments have you tried and with what results?
Your veterinarian will also examine your pet completely, including a neurological examination to determine the severity of the problem as well as localize the level of the spinal cord injury.
Radiographs (X-rays) are usually taken to identify abnormal positioning of the atlantoaxial joint.
Treatment
Medical treatment. Conservative management consists of several weeks of cage rest to allow scar tissue to form, stabilizing the atlantoaxial joint. Steroids are also given for a short time to decrease inflammation of the spinal cord. A neck brace is often used to minimize movement of the neck.
Surgical treatment. There is a high rate of recurrence of symptoms with conservative management, so surgery is often recommended. Surgery is done either to stabilize the joint with pins, cement, wire, or suture, or to fuse the joint. The type of surgery performed depends on the preference of the surgeon. After surgery, the care is similar to conservative management. The prognosis depends on the severity of the neurologic signs before surgery.
Home Care
After surgery, the pet should be cage-rested and restricted from activity for about 4 to 6 weeks. Frequent re-check examinations by your surgeon are necessary to identify potential problems and correct them as soon as possible.
Dogs with this condition should not be bred, since there may be a genetic component to this condition.
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