other name: AA instability
Overview
Atlantoaxial (AA) subluxation is a condition affecting the joint between the first two vertebrae (bones) in the neck: the first bone is called the atlas, and the second bone is the axis. These bones support the skull and allow for a wide range of head motion. Under normal circumstances, the joint is stabilized by several ligaments. When there’s excessive movement between this joint, it is referred to AA instability or subluxation. This instability can compress the spinal cord, leading to neurological issues.
Causes
There are two types of AA subluxation:
- Congenital Atlantoaxial Subluxation:
In animals with atlantoaxial instability present at birth, the ligaments may be underdeveloped or absent, and the dens may be malformed or missing entirely. This form most commonly affects toy breeds and is likely genetic in origin.
- Traumatic Atlantoaxial Subluxation:
Significant trauma to the neck, such as a fall from a height or being hit by a car, can result in ligament rupture or bone fracture, leading to instability at the atlantoaxial joint.
Clinical Signs
Atlantoaxial subluxation can result the following clinical signs: neck pain, low head carriage, wobbliness, inability to walk, or respiratory difficulties. In congenital disease, symptoms before reaching one year of age; however, clinical signs may also appear later in life.
Diagnosis
In severe cases, X-rays of the neck may be sufficient to diagnose this atlantoaxial instability. In other cases, more advanced imaging such as MRI is needed to diagnose the disease and assess the degree of spinal cord compression.
Treatment
Medical and surgical treatment options exist for pets diagnosed with atlantoaxial instability.
- Surgery
The goals of surgery are to relieve pressure on the spinal cord and to stabilize the joint by fusing the affected bones. This is achieved by placing implants that hold the bones in place and prevent any abnormal movement. A CT scan may be needed before surgery to aid in planning. In patients younger than 8 months, surgery is often delayed until the bones have fully matured, as operating too early can increase the risk of serious complications.
Postoperatively, the pet must be STRICTLY rested for at least TWO months to allow proper healing and to prevent serious complications.
- Conservative treatment
In cases where surgery isn’t immediately possible, strict neck immobilization with a custom-fitted brace is essential to stabilize the atlantoaxial joint. This allows time for natural healing or for the patient to mature enough for surgery. The brace is typically kept on for 6–8 weeks, with regular changes. Strict rest is critical, as too much movement can worsen symptoms and lead to further neurological decline. Anti-inflammatory and pain medications are usually prescribed to keep the patient comfortable during recovery.
Prognosis:
The prognosis for dogs and cats with atlantoaxial subluxation depends on the severity of the condition and the chosen treatment. When surgical stabilization is performed successfully, the outlook is often good—many patients show significant improvement and, in some cases, complete resolution of their symptoms. Surgery offers the best chance for long-term success and a return to a normal quality of life, especially when done early, before severe spinal cord damage occurs. However, it’s important to note that this is a complex procedure that does carry some risk of complications.
Animals managed conservatively (without surgery) may show some improvement, but they remain at high risk for relapse or worsening of symptoms. Long-term success with this approach is less predictable, and these patients often require ongoing care with strict exercise restrictions to minimize the risk of worsening.