Atlantoaxial instability in dogs: neck pain and treatment

Overview

Atlantoaxial instability is fairly uncommon in dogs. It affects the spinal junction immediately behind the skull. The first neck vertebra is the atlas, abbreviated to C1. The second is the axis, abbreviated to C2.

There is no ordinary intervertebral disc between these vertebrae. The joint allows the head to turn from side to side. Excessive movement between the vertebrae can damage the nerve structures they protect. Both the degree and duration of compression affect the severity of spinal cord injury.

Causes

Joint support depends on vertebral shape and the ligaments joining the bones. A bony projection at the front of the axis, called the dens or tooth, fits against the atlas and stabilises the junction. An absent or undersized dens is a common abnormality predisposing to instability.

Abnormal dens shape can also interfere with the fit between vertebrae. Ligaments may be underdeveloped or absent from birth. Surrounding muscles and the joint capsule contribute to support. However, failure of the ligament system alone can be enough to cause instability.

Weakened support at the front can gradually stretch a ligament behind the joint. Malformation of the atlas's bony arches may be part of the same group of developmental abnormalities.

Forceful neck bending in an accident can tear the supporting ligaments. The same injury may fracture the dens away from the second vertebra. Even a minor knock may trigger symptoms in a congenitally unstable joint. Injury and inherited structural features may also act together.

Risk factors

The congenital form is most often found in small and toy breeds. Commonly described breeds include Chihuahuas, Pomeranians, and Miniature and Toy Poodles. Symptoms associated with a congenital abnormality often start before 1 year of age. In a group of 14 dogs treated with screw fixation, all were 2–3 years old.

In 41 toy-breed dogs investigated with imaging, median age at symptom onset was 290.00 days. Onset ranged from 30–3,886 days in the same group. Trauma-related instability can occur in a dog of any breed or age.

Jumping off a sofa may be enough to trigger symptoms in an already abnormal joint. Rough play can also worsen symptoms in a genetically susceptible dog.

Typical symptoms

Symptoms may start suddenly or develop gradually:

• Your dog's neck is painful, and this may be the only noticeable sign.

• The head is held abnormally, for example downwards or tilted to one side.

• Your dog is reluctant to move and holds its neck stiffly.

• Walking becomes unsteady and paw placement inaccurate.

• All legs may be weak or give way while standing.

• In severe cases, your dog cannot move its legs at all.

• Breathing may become difficult if neck damage affects the breathing muscles.

Symptoms may ease for a time and then return. Gradual hindleg weakness may also spread to the front legs.

Complications and consequences

Ongoing instability can cause repeated spinal cord compression. Sudden vertebral displacement may cause acute paralysis. Severe neck damage may lead to respiratory arrest and death.

The outlook depends on the severity of existing spinal cord injury and neurological deficits. It is generally better in a mildly affected dog than in a paralysed dog. Even a paralysed dog may recover considerably if compression is relieved and the joint stabilised.

Surgical outcomes have been better in dogs under 2 years old. Symptoms lasting less than 10 months have also been associated with better surgical outcomes. Milder neurological signs are another favourable factor.

However, painful instability can suddenly worsen to become life-threatening.

In a group of 14 dogs treated with screws and bone cement, half, or 7/14, were neurologically normal at 6 weeks. At 6 months, 13/14, or 93%, were neurologically normal and pain-free. Mild neck pain remained in 1/14 dogs, or 7%.

These results included only 14 of 28 dogs operated on. Six were excluded from follow-up because of other systemic diseases. A further 8 were excluded because planned follow-up was unavailable.

Diagnosis at the vet

The vet considers age and breed alongside the symptom history. Neurological examination helps localise movement problems to the neck region. The neck is handled carefully because excessive movement can itself damage the spinal cord.

An ordinary neck X-ray may show an abnormally large gap between the atlas and axis. An abnormal angle between the vertebrae may also be visible. Images assess dens shape and possible fractures. More detailed imaging is needed if X-rays do not establish the diagnosis.

CT shows bone structure in particular detail. It helps plan the placement of surgical fixation devices. MRI provides information about spinal cord damage. It can also investigate congenital ligament abnormalities.

CT images can create a three-dimensional model of vertebral shape for surgical planning. MRI may also reveal spinal cord swelling or bleeding associated with instability.

Before surgery, blood cell testing forms part of the general health assessment. Blood biochemistry helps identify other concurrent diseases.

In young dogs, the dens ossifies at about 7–9 months of age. Incomplete ossification can therefore complicate interpretation of developmental dens abnormalities on early images.

Other concurrent structural abnormalities

In an imaging comparison of 41 affected dogs, a developmental dens abnormality was found in 27/41, or about 66%. Of 34 dogs undergoing MRI, 5 also had syringomyelia. Syringomyelia means fluid-filled cavities forming inside the spinal cord. Concurrent skull and neck abnormalities can affect the choice of surgical approach.

In the same imaging comparison, 22/34 dogs also had abnormal overlap between the atlas and skull. In this situation, the atlas's back arch extends further towards the skull than usual.

Treatment

Options are conservative care and surgery. Conservative care is considered mainly for mildly affected dogs or when other diseases prevent surgery. The vet prescribes pain relief as part of treatment.

Rest and external support

Conservative care includes a rigid neck brace and strictly controlled rest for 6–8 weeks. The aim is for scar tissue forming around the immobilised joint to help stabilise it. However, the brace does not always keep the joint stable. With long-standing symptoms, complete recovery without surgery is less certain.

A neck brace can cause skin rubbing and pressure sores. Eye ulcers may also occur as a brace-related complication. A dog unable to walk needs substantial daily help from its carer.

With conservative care, a fracture of the dens or vertebral body may fail to unite.

Surgical stabilisation of the joint

Surgery is often recommended because of the risk of recurrent symptoms and further spinal cord injury. It relieves pressure on the spinal cord. The aim is to stabilise the joint permanently. Returning the vertebrae to their normal position usually reduces compression.

A malformed dens pointing towards the spinal cord sometimes needs removal. Fixation commonly uses screws or pins and bone cement from below the joint. A bone plate may also be used. Approaching from below allows removal of joint cartilage and placement of a bone graft to support fusion.

Stabilisation techniques from above the joint are also used. Limited bone and the nearby spinal cord make precise implant placement demanding. The procedure requires a surgeon experienced in it.

Fixation material can move or break. A misplaced implant can cause ongoing pain or compress the spinal cord. Fixation material may then need removal. One of the most serious risks is respiratory arrest from spinal cord injury during surgery.

Swallowing difficulties may develop in connection with surgery. Airway complications include laryngeal paralysis. Pneumonia can also complicate recovery.

Reported surgical mortality is 0–10%.

Monitoring recovery

Strict rest for 6–8 weeks is usually needed after surgery. A neck brace may provide additional support afterwards. Follow-up X-rays are often taken at 4 and 8 weeks to assess fixation and healing.

After screw and bone cement fixation, recovery may allow the brace to be removed at the 6-week imaging review. If fixation is sound, walking can then increase gradually for another 6 weeks before full activity.

Prevention

A dog with diagnosed instability needs protection from further neck injuries over the long term too. Even a small knock to an already abnormal joint can cause ligament failure. Jumping down from furniture is one possible source of this minor trauma.

Prevent other dogs from jumping onto a dog with an unstable neck during play.

Collars and other equipment putting pressure on the neck are avoided after surgery. Do not manipulate a suspected or confirmed unstable neck at home.

Important for dog owners

Temporary symptom relief does not rule out intermittent instability. Neck pain can occur without paralysis.

Record when symptoms began and any fall, jump or other injury beforehand. Watch whether your dog can walk, whether head posture changes and whether breathing becomes difficult. Before discharge, ask how to lift and transport your dog without straining its neck.

Avoid sudden exertion and jumping during recovery. Care may include supporting short walks with a sling.

Agree in advance on brace and skin checks and follow-up imaging. Keep investigation reports and procedure details.

Some breed-club health information programmes ask owners to report spinal problems to the breeding committee.

Frequently asked questions

Is neck vertebral instability the same as a slipped disc?

There is no intervertebral disc in the joint between the first and second neck vertebrae. Atlantoaxial instability involves excessive movement of this joint. It can cause spinal cord compression and neck pain. Diagnosis relies on imaging as well as symptoms.

Can my dog have the condition while walking normally?

Neck pain may be the only symptom. Some dogs have intermittent signs. Nevertheless, significant joint instability can suddenly worsen. Do not try testing the neck by bending it yourself. X-rays or more detailed imaging may be needed for diagnosis.

Is an X-ray enough for diagnosis?

An X-ray may establish abnormal alignment between the vertebrae. However, it does not show the spinal cord in the same way as MRI. CT defines bone structure for surgical planning. MRI helps assess spinal cord injury. It can also investigate ligament structure.

Can a neck brace replace surgery?

A mildly affected dog can sometimes be treated with a neck brace and rest for 6–8 weeks. However, not every dog recovers with this approach. Ongoing instability can cause further displacement and paralysis. Brace-related skin damage is also possible.

How long does my dog need rest after surgery?

Strict rest usually lasts 6–8 weeks after surgery. X-rays often monitor fixation healing at 4 and 8 weeks. After review, a further 6-week gradual return to normal walks may be needed.