Spinal Cord Malformation in Dogs

Atlantoaxial instability or luxation is a rare condition that can happen when the connection between a dog’s first and second cervical vertebrae becomes damaged. These two bones in the neck are called the atlas and the axis. The atlas (C1) is shaped somewhat differently than the other vertebrae, but it is normally supported by the dens, a vertical spine that protrudes from the axis (C2). The two bones are also connected by a system of ligaments. If the cervical spine is forcefully flexed too far in one direction, the dens can fracture and the ligaments can tear causing the atlantoaxial joint to become unstable. The spinal cord may become pinched between the vertebrae, causing pain, neurological symptoms and sometimes even paralysis. In most dogs, it takes a severe injury with a significant amount of pressure on the neck for this to happen. However, some small and toy breeds have a genetic tendency to develop atlantoaxial luxation; the dens may be missing or malformed, or the ligament attachment is not as well developed as it should be. Affected dogs may develop symptoms as a result of daily physical activities, like jumping down from an owner’s lap or running quickly down the stairs. Most symptoms occur within the first year of life. Surgical treatment can be successful, depending on the severity and duration of the condition. Occasionally, in cases where the spinal cord is severely pinched, respiratory paralysis may occur very suddenly and owners will find the dog dead before they are able to seek treatment.

If the connection between the first and second vertebra in the neck is not properly developed it causes instability in the joint. This is an inherited spinal malformation called atlantoaxial luxation. It is more common in small and toy breeds. Symptoms can be quite severe if the spinal cord becomes pinched between the vertebrae.

Symptoms are more common in small dogs, but any dog could develop atlantoaxial luxation after an injury to the neck. Seek veterinary treatment as soon as possible.

• Severe neck pain
• Holding the head at an unusual angle
• Muscular weakness (paresis)
• Inability to stand
• Paralysis
• Inability to control one or more limbs
• Diaphragm paralysis and respiratory failure (in severe cases)

Types

There are several different types of atlantoaxial luxation. 

• Acquired – many kinds of trauma can cause acquired instability through fracture of the dens or the axis
• Congenital – inherited developmental malformations, missing or abnormal dens, lack of connection between the atlas and axis
• Acute – symptoms for less than thirty days
• Chronic – symptoms for more than thirty days

There are two causes for atlantoaxial luxation.

Inherited

• More common in small breeds 
• Yorkshire Terriers, Chihuahua, Poodle, Pomeranian, and Pekinese
• Usually appears in the first year of life

Injury

• A condition that causes forceful flexion of the head or neck

If your dog is in the first year of life and belongs to a breed with a high rate of incidence, this will make an inherited condition more likely. Symptoms and family history will help the veterinarian diagnose atlantoaxial luxation. Dogs that have recently suffered an injury to the neck can also be at risk.

A definitive diagnosis is made with X-rays and or a CT scan of the cervical spine. Your dog may need to be anesthetized during the process, especially if he is in severe pain. The veterinarian will need to take several different angles to see how the vertebrae are interacting as the spine moves. There may be increased space between the atlas and axis; missing or abnormally shaped dens and fractures in the bone may also be visible on the X-ray. The veterinarian will take care to avoid putting pressure on the neck and further injuring your dog.

Surgery is the most effective treatment for dogs with atlantoaxial luxation. The surgery is fairly complex and your veterinarian will likely refer you to a specialist. The dens may need to be removed and some means of stabilizing the joint will need to be inserted. Bone grafts, bone plates, pins, or screws may all be used to help fuse the joint. The surgeon’s exact approach will depend on your dog’s condition as well as personal preference and experience. There is a certain amount of risk. Errors that injure the spinal cord can be fatal, and badly placed supports can make the problem worse and need removed. Your dog will need to rest for 6-8 weeks after surgery and likely have to wear a neck brace during healing. Follow-up X-rays may be necessary to assess the effectiveness of treatment.

If symptoms are mild, or your dog is not healthy enough for surgery, more conservative treatment may be recommended. This usually includes at least 6-8 weeks of cage rest, during which time your dog will need to wear a splint or a brace. Allowing the joint to heal in a stable position can develop enough scar tissue to support the bones. There is a high risk of recurrence with this treatment and your dog will need to limit activity throughout life. A permanent neck-brace may be necessary to further stabilize the joint. Skin breakdown from wearing the brace can sometimes be a problem. Pain medication and skin creams may be prescribed to help manage the side effects of this treatment.

Successful surgery can allow your dog to make a complete recovery. Some symptoms may still need to be managed after surgery with pain medication and/or a neck brace. Conditions that are mild to begin with can also often be effectively managed in this way. Your dog may need to limit activity and avoid any situation that could put pressure on the neck.

Your dog’s prognosis depends on how severe the condition is to begin with. In general, acute symptoms that have only just begun to manifest are more treatable than chronic ones. The veterinarian will discuss your dog’s chances of recovery after looking at the exact bone placement on an X-ray.