Citation

Ivancic PC. Spine 2011; 37(12): 1022-1029.

Affiliation

From:Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut, USA.

Copyright

(Copyright © 2011, Lippincott Williams and Wilkins)

DOI

10.1097/BRS.0b013e31823fd92d

PMID

22089395

Abstract

Study Design. An in vitro biomechanical study.Objectives. To investigate atlas injury mechanisms due to horizontally-aligned head-first impacts of a cadaveric neck model and to document atlas fracture patterns and associated injuries.Summary of Background Data. Experimental atlas injuries have been created by applying compression or radial forces to isolated C1 vertebrae, dropping weight or applying sagittal moments to upper cervical spine segments, or vertical drop testing of head-neck specimens or whole cadavers. Atlas injuries that commonly occur due to horizontally-aligned head-first impacts have not been previously investigated.Methods. Horizontally-aligned head-first impacts into a padded barrier were simulated at 4.1 m/s using a human cadaver neck model mounted horizontally to a torso-equivalent mass on a sled and carrying a surrogate head. Atlantal radial force was computed using head and neck load cell data. Post-impact dissection documented atlas and associated injuries. Average atlantal radial force peaks and their occurrence times were statistically compared (P<0.05) among the first local and global peaks using paired t-tests.Results. The first average local peak in radial atlantal force was significantly smaller (1,240 vs. 2,747 N) and occurred significantly earlier (24 vs. 46 ms) than the global force peak. Atlas injuries consisted of either 3- or 4-part burst fractures or incomplete lateral mass fracture unilaterally. Associated injuries included bony avulsion of the transverse ligament unilaterally and fractures of the occipital condyles, superior facets of the axis, or odontoid.Conclusions. Our results indicated that the varied atlas fracture patterns were due primarily to radial forces causing outward lateral expansion of its lateral masses. Anterior and posterior arch fracture locations are dependent, in part, upon the cross-sectional arch dimensions. Transverse ligament rupture or bony avulsion is likely associated with real-life atlantal burst fractures.

Language: en