Atlanto-axial Subluxation
Atlas - First Cervical Vertebrae
Axis - Second Cervical Vertebrae
Atlanto-Axial Joint - The joint between the 1st and 2nd Cervical Vertebrae
This joint is unique compared to other vertebrae joints, in that there is no disc between the atlas and axis. Instead it is supported and stabilised by ligaments. The main purpose of this joint is to enable the patient to move their head from side to side.
What is a AA subluxation?
AA subluxation is essentially a disruption in the alignment of the Atlas and Axis. This means that the joint becomes unstable and results in excessive movement of the neck.
What problems does this cause?
As a result of this type of subluxation the nerves that form the spinal cord, which runs through the vertebral column can become compressed resulting in neurological deficits and neck pain.
Trauma to the neck such as forced flexion of the head causing ligament/vertebrae damage can result in this condition. However, it is often congenital and usually arises from an abnormality in the Axis either due to a issue with the supporting ligaments or because the Dens ( a projection of the Axis that fits with the Atlas) is malformed or absent.
How common is this congenital abnormality?
This type of abnormality is most common in toy breeds such as: Yorkshire Terriers, Chihuahua’s, Pomeranians and Pekingese. It usually occurs within the first year of life.
Neck pain - yelping and crying when lifted or touched in the neck/head region
Ridgity of the neck - A reluctance to flex the neck or move, eat and drink
Paraparesis/Paresis - Resulting in the patient being anything from non-ambulatory or ataxic
How is the condition diagnosed?
Radiographs - Lateral, Ventro-dorsal and Oblique views are recommended.
MRI - This will allow assessment of spinal cord damage.
CT - This will allow visualisation of bone deformity in regards to the vertebrae.
What are the treatment options?
Conservative - Often only offered to patients with mild clinical signs. It includes cage rest for 4-6 weeks and often the patients are put in a neck brace for this time to allow fibrous scar tissue to form and stabilise the joint.
Surgical - The main aims of surgery are to relieve compression of the spinal cord and stabilise the joint permanently. If the dens is malformed or damaged, it may have to be removed. The recommended surgical approach is ventrally, as it allows arthrodesis (fusion) of the atlanto-axial joint. A cancellous bone graft is placed in the joint and pins or screws are placed across the joints. A head brace is then put in place and should remain on for 4-6weeks.
Avoid flexion of the neck - this will cause further compression of the spinal cord and may result in severe neurological issues.
Gentle Physiotherapy - Often these patients do not move either due to fear of pain or they are unable to because of the spinal cord compression. Therefore physiotherapy is important to maintain muscle tone and blood flow to the limbs
Feeding Tubes - Dependent of the neurological condition of the patient a feeding tube may be the best course of action to ensure they are maintaining hydration status and meeting their RER.
Supportive Bedding - Patients that have limited movement are prone to bed sores therefore padded supportive bedding is essential. The use of donut bandages around boney joints may be needed.
Prevention of Urine Scalding - Using inco pads to soak up urine and regular baths to get urine off skin will be needed.
Being aware of complications - Further displacement of the dens (as a result of surgical failure or neck flexion) into the spinal canal can lead to diaphram paralysis, respiratory failure and death. Thus monitoring of Res rate and effort is a must.
The prognosis depends on the degree of spinal cord trauma and neurological deficits present before treatment. Mild clinical signs result in a good prognosis whereas prognosis for dogs with paralysis is guarded, although recovery is possible with successful surgery.
