What is atlantoaxial subluxation?
A cat or dog’s spine is made up of dozens of small bones called vertebrae, including several cervical bones in the neck. The first cervical vertebra is called the atlas and the second is the axis, and together these bones form the atlantoaxial (AA) joint, which is connected by ligaments. Designed as a pivot joint, the atlantoaxial joint allows your pet to move their head from side to side.
Atlantoaxial subluxation is an uncommon condition that results in partial dislocation of the atlas and axis vertebrae, occurring when the connection between the two bones is unstable. This subluxation causes abnormal or excessive movement of the AA joint, leading to neck pain and compression of the spinal cord. The severity of the compression depends on the duration of the condition, when treatment is sought and the amount of pressure put on the spinal cord.
Although atlantoaxial subluxation can occur in any breed of dog or cat as the result of an injury, it’s usually the result of a birth defect, such as an abnormality of the ligaments or axis. These abnormalities mean subluxation can occur as the result of minimal trauma (if any), such as jumping off the sofa or playing with another dog. The condition is usually seen in toy breeds of dogs, such as chihuahuas, poodles, Pomeranians and Pekingese, and can normally be spotted when the dog is less than one year old.
What are the symptoms?
Animals suffering from atlantoaxial subluxation might show symptoms gradually, or they might start displaying signs very suddenly. The severity of the symptoms depends on the degree of spinal cord injury, with clinical signs ranging from weakness and an uncoordinated gait to a complete inability to stand or walk. You might notice your pet showing signs of neck pain, such as crying, yelping, stiffness of the neck and difficulty lowering their head to eat. Severe spinal cord injuries can lead to complete paralysis from the neck down, which results in a paralysis of the animal’s diaphragm, leaving them unable to breathe. These cases are often very sudden and are normally fatal.
Other atlantoaxial subluxation symptoms include:
- Mild to severe neck pain
- Holding the head low
- Weakness in all four legs
- Inability to stand or move the legs
- Difficulty breathing
If your pet presents any of the above clinical symptoms, atlantoaxial subluxation may be suspected, particularly if they’re one of the breeds prone to birth defects. To confirm the diagnosis, a vet will usually take an x-ray of the neck to identify any obvious dislocation or misalignment of the vertebrae. However, while an x-ray can usually confirm a diagnosis of AA subluxation, it cannot determine the severity of the spinal cord injury. For this, more advanced imaging techniques may be needed. To evaluate the spinal cord for compression and damage, your vet might recommend a magnetic resonance imaging (MRI) scan.
In some cases, a vet may need to take cerebrospinal fluid (CSF) from around the spinal cord and send it to a laboratory for analysis, allowing them to rule out other spine conditions. If your pet needs to have CSF taken, a lumbar puncture will be performed.
How do we treat atlantoaxial subluxation?
Treatment for atlantoaxial subluxation can be surgical or conservative, depending on the severity of the condition. Your specialist will be able to advise on the best course of action for your pet.
Conservative management: If your pet is only suffering from mild symptoms, or if your pet has other medical conditions that make them a poor candidate for surgery, conservative management is likely to be recommended. This involves strict cage rest, along with your pet wearing a neck brace for several weeks. Painkillers and steroids may also be recommended to manage your pet’s discomfort. Although complete recoveries have been reported through conservative management, it’s likely your dog will suffer from continued instability, with an ongoing risk of sudden paralysis and death.
Surgery: Because of the risk of deterioration and paralysis with conservative management, surgery is usually the preferred course of action for treatment. The aim of surgery is to relieve the pressure on the spinal cord by fusing the atlas and axis vertebrae together into a normal position, enabling the spinal cord to heal. The preferred approach involves placing surgical screws into the atlas and axis bones and connecting the screws with bone cement, aiming to stabilise the atlantoaxial joint. The surgery has a success rate of 90%, compared to a 50% success rate for conservative management.
During the recovery period, animals with neck braces are often re-evaluated weekly. Animals who’ve had surgery will need to be evaluated between four and eight weeks after the surgery, during which time you’ll need to monitor your pet for any new or recurring symptoms.
The prognosis for atlantoaxial subluxation depends on how it’s managed. Although conservative treatment can improve your pet’s condition, there is a high chance of pain and spinal cord injury recurring, especially once the neck brace is removed.
The good news is that surgical treatment for atlantoaxial subluxation has a high success rate, especially for young dogs with mild symptoms. Surgery has a lower chance of success for older dogs or those suffering from more acute symptoms, such as paralysis, but significant recovery is still possible.
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