Atalantoaxial dislocation may be congenital due to abnormal development (non-fusion of odontoid with the axis, agenesis of odontoid or transverse ligament of the atlas) or acquired following trauma like sudden flexion of the neck or may follow vertebral tuberculosis, rheumatid arthritis and ankylosing spondylitis.
In the atlanto axial joint, the odontoid process is encircled by the anterior arch of the atlas ventrally, by the transverse atlantal ligamentous complex dorsally. The apical and two alar ligaments fix the tip of the odontoid process to the occiput.
A wide range of lateral and rotational movements are maintained without any dislocation. However; in congenital or acquired conditions, there are greater chances of anterior or posterior dislocation of the joint. As a result, the effective antero posterior diameter of the spinal canal during neck flexion is reduced.
Clinically there may be a sudden or gradual onset. There is pain in the neck, suboccipital region and restriction of neck movements. Progressive spastic quadriparesis, impairment of sensations in the extremities, wasting of the small muscles of the hands and difficulty in walking are other manifestation.
Neurological features of Atalantoaxial dislocation are precipitated by even small trauma in the neck. In majority of patients the neurological deficit is progressive while in only small percentage it may be transitory. Features of unconsciousness, vertigo, blackouts and drop attacks may occur especially when turning the head suddenly to one side.
Long standing cases of A-V dislocation may develop syringomyelia or atropy of the spinal cord.
Diagnosis of Atalantoaxial dislocation is made by plain X-ray of the cervical spine in lateral view with head and neck in full flexian and extended position. An increase in the atlanto axial distance (anterior surface of the odontoid and anterior arch of atlas) is diagnositic (normal distance less than 3 mm). Further confirmation is made by MM.
Treatment is surgical (Fusion of axis to the basiocciput).
In cases of reducible atalantoaxial dislocation, intermittent or continuous traction is done followed by a stabilization procedure where bone grafting is done. In patients who are not willing for surgery, cervical collar in neutral or slightly extended position is advised, In cases with acquired disease (Tuberculosis, rheumatid arthritis) appropriate medical treatment is advised.