Occipitalization of the atlas: its incidence and clinical implications.

OBJECTIVE The aim of the present study was to investigate the incidence of occipitalization of the atlas among Thai dried skulls, in order to contribute to baseline awareness of this condition. MATERIALS AND METHODS The skulls of 633 adult Thais from the collection maintained in the Department of Anatomy, Faculty of Medicine, Khon Kaen University, Thailand, were examined for evidence of occipitalization of the atlas. The skulls were well-preserved and did not show any traits of craniofacial deformation. The skulls for which the age and sex were unknown were excluded from the analysis. From the cadaveric records on each individual, we learned that the skulls belonged to 373 men (age of decease between 25 and 90 years), and 260 women (age of decease between 28 and 92 years). RESULTS Occipitalization of the atlas was detected in 2 skulls (0.32%). The first case was a male skull (54 years of age at decease), where the atlas was partially fused to the occipital bone. The second case was also a male skull (59 years of age at decease) showing complete fusion of the anterior arch of the atlas. CONCLUSION The incidence of occipitalization of the atlas is low; however, if present this abnormality may cause a wide range of neurological problems. Knowledge of occipitalization of the atlas may be of substantial importance to orthopedists, neurosurgeons, physiotherapists and radiologists dealing with abnormalities of the cervical spine. Mistaken diagnoses have led to delayed treatment and at times adverse results.