The Corona Dentis: Description of an Anatomical Variant with Technical Implications for Anterior Odontoid Screw Placement.

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The Corona Dentis: Description of an Anatomical Variant with Technical Implications for Anterior Odontoid Screw Placement.

World Neurosurg. 2017 May 13;:

Authors: Alonso F, Iwanaga J, Chapman JR, Oskouian RJ, Tubbs RS

Abstract
INTRODUCTION: Type 2 odontoid fractures are the most common cervical fractures among the elderly. Neurological deficit is usually caused as a result of myelopathy due to posterior dens migration. Direct anterior screw placement provides stabilization and can preserve C1-C2 movement. The presence of a bony excrescence on the anterior superior tip of the dens may lead to placement of a screw of incorrect length.
METHODS: Twenty C2 dry specimens were examined for the presence of a corona dentis, which is a bony excrescence in the coronal plane near the apex of the dens. When identified, measurements of the corona dentis were performed using calipers and a ruler. Additionally, AP and lateral fluoroscopy was performed on all specimens found to have a corona dentis.
RESULTS: A corona dentis was found on 20% of our C2 specimens and had an average width of 9 mm and an average height of 4.5mm. The average width of the dens did not vary as the normal tip of the dens transitioned into the coronae. In no specimen did the corona dentis appear to be composed of trabecular bone and it was seen as superior projection of cortical bone on fluoroscopy. On fluoroscopy, the corona dentis could be identified on a true AP projection. In angulated AP views, fluoroscopic images overestimated the length of the corona dentis.
CONCLUSIONS: We describe a new entity termed the "corona dentis" owing to its crown-like feature. It is a superior cortical bone protrusion and should be noted as a variant of the dens during anterior odontoid screw placement. Its propensity to increase the height of the dens markedly can lead to higher rates of neurological deficits during type 2 odontoid fractures if not appreciated. A true AP view is critical for correct screw size placement.

PMID: 28512042 [PubMed - as supplied by publisher]

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