• Emir Benca, Ivan Zderic, Kenneth P van Knegsel, Jan Caspar, Lena Hirtler, Christoph Fuchssteiner, Andreas Strassl, Boyko Gueorguiev, Harald Widhalm, Reinhard Windhager, and Peter Varga.
• Department of Orthopedics and Trauma Surgery, Medical University of Vienna, Vienna, Austria.
• Spine. 2022 Sep 1; 47 (17): 1212-1220.

Study DesignLaboratory study.ObjectiveThis study aimed to investigate the biomechanical competence and fracture characteristics of the odontoid process.Summary Of Background DataOdontoid fractures of the second cervical vertebra (C2) represent the most common spine fracture type in the elderly. However, very little is known about the underlying biomechanical fracture mechanisms.Materials And MethodsA total of 42 C2 human anatomic specimens were scanned via computed tomography, divided in six groups, and subjected to combined quasistatic loading at -15°, 0°, and 15° in sagittal plane and -50° and 0° in transverse plane until fracturing. Bone mineral density (BMD), height, fusion state of the ossification centers, stiffness, yield load, and ultimate load were assessed.ResultsWhile lowest values for stiffness, yield load, and ultimate load were observed at load inclination of 15° in sagittal plane, no statistically significant differences were observed between the study groups ( P ≥0.235). BMD correlated positively with yield load ( r2 =0.350, P <0.001) and ultimate load ( r2 =0.955, P <0.001) but not with stiffness ( r2 =0.082, P =0.07). The specimens with clearly distinguishable fusion of the ossification centers revealed less data scattering of the biomechanical outcomes.ConclusionLoad direction plays a subordinate role in traumatic fractures of the odontoid process. BMD was associated with significant correlation to the biomechanical outcomes. Thus, odontoid fractures appear to result from of an interaction between the load magnitude and bone quality.Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.

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