Atlantoaxial instability is an uncommon condition of dogs in which there is abnormal movement or instability in the cervical spine or neck, between the atlas (first cervical vertebra) and axis (2nd vertebra). This instability allows abnormal bending between the two bones, which causes pressure or compression of the spinal cord. The severity of the injury to the spinal cord depends both on the amount of pressure, and the duration of the condition.
The atlantoaxial joint is normally stabilized by a projection off the axis called the dens, which fits into the atlas, as well as several fibrous attachments (ligaments) between the two bones. There are two causes for the instability – trauma and birth abnormalities. Traumatic instability occurs after forceful flexion of the head, causing either fracture of the dens or other part of the axis, and/or tearing of the fibrous attachments. This form of the instability can occur in any breed, at any age. (1-4) |