Atlantoaxial luxation typically affects young, small breed dogs such as the Yorkie, Toy Poodle, and Chihuahua but any breed or age can be affected.
Clinical signs may include neck pain, abnormal head carriage, weakness in all four legs, or inability to use the legs. Atlantoaxial luxation occurs when there is instability between the first and second cervical vertebrae (bones of the neck). These two bones are normally firmly attached to each other with a series of ligaments. Diagnosis is based on radiographs that demonstrate the instability, however, MRI and CT are useful in identifying concurrent problems and in surgical planning. Surgery offers the greatest chance of long-term resolution of signs.
The atlas is the first bone in the neck (C1). The axis is the second bone in the neck (C2). The atlas is unique from the other bones of the neck in that it has no dorsal spinous process and two large lateral processes (wings). The axis has a process, called the dens, that extends cranially. The atlas and the axis are connected to each other by a series of ligaments. In several toy breeds, the dens is malformed. With minimal or no trauma, the ligaments can fail and instability between the atlas and axis ensues. This leads to spinal cord compression.
Clinical signs of atlantoaxial luxation may include neck pain, abnormal head positions (head tilt, holding the head down, etc), wobbliness of all four legs, weakness of all four legs, inability to stand, or inability to move the legs.
Atlantoaxial Luxation Before Surgery
Plain radiographs in a neutral and gently flexed positions can demonstrate instability in the C1-C2 joint. Myelography is contraindicated for several reasons: flexing the cervical spine excessively can exacerbate the compression, and myelography may cause seizures that can lead to serious complications. Computed tomography (CT) can show bony abnormalities such as fracture of the dens and cranial displacement of the atlas into the foramen magnum. Magnetic resonance imaging (MRI) is useful in identifying injuries to soft tissues and finding concurrent problems such as caudal occipital malformation syndrome, syringomyelia, and meningoencephalitis.
Flexed Lateral Radiograph
Reconstructed CT showing malformation of C2 and dorsal deviation of the dens
Post operative radiograph showing proper alignment of C1-2 and stabilization using screws into C1 and C2