The Occipital-Atlantal Joint

The OA joint may be the area that gets the most attention in my patients, and often shows up on my reports to referring vets, in some cryptic form, or on the insurance form as a dysfunction or subluxation. Today I saw a dog with ear pain, which the regular vet had had a hard time examining yesterday because of guarding and tension in the neck (okay, the owner said he was shrieking and wouldn't let them look deep in the ears). The OA joint was rotated, and after mobilization, I was able to see all the way to the eardrums, as well as the amount of debris that was causing irritation.

I often describe OA problems as feeling like tension headaches that arise from muscle tightness at the base of the skull and may radiate up around the ears and over the brow, where heat may be evident. It can result in tightness in the back of the throat, pressure or ringing in the ears. The dogs often yawn or shake the head after the joint tension is released.

Chronic ear problems or ear canal redness without discharge may be an indicator. These dogs may have a slight imbalance in the set of their ears, and if observed closer, their eyes and their whole head is slightly askew. Cavalier King Charles Spaniel dogs with Chiari-like malformations are the classic cases of this dysfunction, but any dog may be affected.

The most common cases observed in general practice will be geriatric vestibular syndrome (GVS) dogs. The primary problem is usually in the inner ear, but the muscle tension through the neck, combined with the dog’s desire to rotate the head to find balance, results in a secondary, fixed rotation at the OA joint, as well as increased muscle tension along one side of the neck, which exacerbates the wry neck and inability to stand or walk straight. If a current rehab patient is subsequently afflicted with GVS, I will encourage owners to bring them in for manipulation in the first couple of days to break the OA dysfunction component.

What is actually going wrong with the OA joint? It is a combination of bone slippage (subluxation of the rounded base of the skull in the cup of the first cervical vertebra) in one direction, instead of the normal rolling motion, then increased muscle and ligament tension (reflex inhibition , an unconscious protective mechanism) to prevent further slippage. This pinches the first cervical nerve, which affects the muscles along the back of the throat, front of the neck, inside of the jaw, back and sides of the head, and the ears. Also affected are very important muscular proprioceptors in the neck which provide postural feedback and affect overall muscle tone throughout the body. The dogs can no longer move fluidly to adjust for slight imbalances and use gross motor movements rather than finer movements to adapt. This leads to more jerking of the neck and head and a continual vicious cycle.

The cycle can be initiated by a variety of insults to the body. An illness with generalized muscle weakness or fever with muscle stiffness may be the cause. Lameness with a persistent head bob in one direction may lead to an OA problem, and the problem may continue as long as the lameness does, or until a better gait develops. Animals get whiplash from being in or being hit by vehicles. Even slipping or tripping can cause a dysfunction when the head jerks at the end of the neck.

Big dogs need strong necks to hold their heads steady, but it is the relative velocity of the head at the end of the neck, and the relative size of the head to the neck, so small dogs and cats are at risk as well. The other cause is compressive injury where the animal runs head-on into something or someone, or has a glancing blow off something, causing the head to bend tightly at the OA joint and pressing the bones to slide across each other instead rolling.

So the next time your pet seems to be looking at you sideways, or from under raised brows, look again. Is that dog able to move its’ head fully, or is it moving just the neck? Are those eyes and ears level? What about the line of the nose?