Atlantoaxial Subluxation
Quick Facts
Atlantoaxial subluxation is a serious cause of pain and weakness resulting from instability between the first two vertebrae in the neck.
Congenital malformations of the dens and transverse ligament of the atlas in toy breed dogs such as Yorkshire Terriers, Chihuahuas, Pomeranians, Maltese and Toy Poodles are the most common underlying cause of atlantoaxial subluxation.
There are medical and surgical treatment options for patients with atlantoaxial subluxation. The neurologists at GCVS will recommend the best treatment options based on your pets symptoms and examination.
Definition: Atlantoaxial subluxation is excessive movement or instability between the first (C1, atlas) and the second (C2, axis) cervical vertebrae.
Clinical Picture: Most atlantoaxial subluxations in veterinary medicine occur because of congenital malformations in small breeds of dogs, however, traumatic atlantoaxial subluxation can also occur in any breed. Malformation or absence of a portion of the axis called the dens, abnormal angulation of the dens, separation of the dens from the axis and malformation or absence of the transverse ligament of the atlas are the more common abnormalities associated with congenital atlantoaxial subluxation. Most patients with congenital malformations develop symptoms of neck pain and weakness within the first year of life, but development of symptoms at a later age can also occur. Symptoms of atlantoaxial subluxation range from neck pain to weakness or paralysis in all limbs. For some patients compression of the cervical spinal cord may be severe enough to cause respiratory paralysis, symptoms referable to the lower brainstem such as trouble swallowing, poor balance, inability to bark and death. Symptoms usually have a sudden onset, however, slowly progressive or intermittent symptoms occur less frequently.
Diagnosis: Radiography is often sufficient to make a diagnosis of atlantoaxial subluxation. Excessive distance between the arch of C1 and the spinous process of C2, as well as upward and forward displacement of C2 into the spinal canal are the most frequent findings of atlantoaxial subluxation visible on lateral radiographs of the vertebral column. In some patients, slight flexion of the neck is necessary to demonstrate the instability between C1 and C2. Extreme care should be taken to avoid excessive flexion of the neck as this can increase spinal cord compression. Ventral-dorsal images (patient on their back) or oblique images are most useful to evaluate the size or presence of the dens. CT imaging may also be useful to obtain measurements of the bodies of C1 and C2 for implant placement and to demonstrate spinal cord compression from abnormal angulation of the dens.
Treatment: There are both medical and surgical treatment options for patients with atlantoaxial subluxation. Medical therapy consists of anti-inflammatory and pain medication along with splinting of the neck and strict exercise restriction for 6-12 weeks. Patients suffering from their first episode of pain only or very mild neurologic may respond to medical management, but reoccurrence of symptoms can occur. For patients with repeat episodes of pain or more significant weakness, surgical stabilization of C1 and C2 is recommended. Several surgical techniques have been described to stabilize the atlantoaxial subluxation, with surgical approaches from above and below the vertebral column. At GDVS an approach from below the vertebrae using a combination of screws, wires, surgical cement and bone grafting are most often employed to stabilize the C1 and C2 vertebrae.
Prognosis: The prognosis for patients with atlantoaxial subluxation is variable and is dependent in large part to the severity of neurologic deficits caused by the instability. Respiratory paralysis and death before or after surgery is a concern for the most severely affected patients. Reoccurrence of symptoms may also occur for patients treated with a splint (medical treatment) or for surgical patients due to implant migration or failure. Despite these challenges, however, many patients with atlantoaxial subluxation can be successfully treated and live a long and pain free life.
Aftercare: Patients with atlantoaxial subluxation will benefit from strict exercise restriction in a kennel during medical management with a splint and for a shorter period of time following surgery. If surgery has been performed radiographs of the surgical implants are often obtained at some of the recheck evaluations. For patients with the most severe weakness, physical therapy in the time following surgery will help maximize their recovery.