A MORPHOLOGICAL STUDY OF PONTICULI OF THE HUMAN ATLAS VERTEBRAE AND ITS CLINICAL SIGNIFICANCE

BACKGROUND: The first cervical vertebra, atlas plays a vital role in the movement of skull & neck. The anatomy of atlas is complex due to its three dimensional structure. There is a groove on superior surface of posterior arch of atlas for passage of 3 rd part of vertebral artery and first cervical spinal nerve (suboccipital nerve). Sometimes the oblique ligament of atlas which is present at the lower border of posterior atlanto-occipital membrane may ossify and convert this groove into a foramen. This foramen may be complete or incomplete, In some cases a bony bridge also extends from lateral masses of atlas to the posterior root of transverse process and form an additional foramen through which vertebral artery travels. The vertebral artery is prone to compression in its entire course between foramen transversarium and foramen magnum during extreme rotation movement of head & neck. This condition may be aggravated by the presence of these ponticuli & results in compromised blood flow and causes vertebrobasilar insufficiency presenting with dizziness, fainting, vertigo, transient diplopia & various neurological disturbances. MATERIALS & METHODS: The present study was carried out on 118 (Male-62, Female-56) dried fully ossified adult human atlas of known sex for the presence of complete or incomplete ring for vertebral artery i.e. different ponticuli on the superior surface of the atlas vertebra. RESULTS: We observed 21.17% cases of ponticulus posterior in which 7.62% specimens had complete ring while 13.55% specimens had incomplete ring & ponticulus lateralis was reported only in 5.93% cases (unilateral: 2.54% & bilateral: 3.39%). Incidence of ponticulus posterior as well as lateralis were more common in male as compared to female. Complete ponticulus posterior was more common in right side, while incomplete ponticulus posterior as well as ponticulus lateralis were more commonly bilaterally. CONCLUSION: As indicated by our study, ponticulus posterior as well as lateralis are not so rare anomaly in the population of Bihar. So, the detail knowledge about these variations is very helpful to the neurophysicians, neurosurgeons, orthopedicians & otolaryngologists who faces regularly the patients complaining about the symptoms of vertebrobasilar insufficiency. These informations are also important for the spine surgeons to prevent vascular complications during spinal surgeries especially in those patients who required screw placements in the lateral mass of atlas.