STUDY DESIGN: Laboratory study.
OBJECTIVE: This study aimed to investigate the biomechanical competence and fracture characteristics of the odontoid process.
SUMMARY OF BACKGROUND DATA: Odontoid fractures of the second cervical vertebra (C2) is the most common fracture type in cervical- and spine in general in the elderly. However, very little is known about the underlying biomechanical fracture mechanisms.
METHODS: A total of 42 human C2 specimens were Scanned using a QCT, divided in 6 groups, and subjected to combined quasi-static loading at -15°, 0°, and 15° in sagittal plane and -50° and 0° in transverse plane until fracture. Bone mineral density (BMD), height, state of the fusion of the ossification centers, stiffness, yield load, and ultimate load were assessed.
RESULTS: While the lowest values for stiffness, yield, and ultimate load were observed at load inclination of 15° in the sagittal plane, no statistically significant differences could be observed between the six groups (P=0.235, P=0.646, and P=0.505, respectively). BMD was positively correlate with the yield (r²=0.350, P<0.001), and ultimate load (r²=0.955, P<0.001), but not with the stiffness (r²=0.082, P=0.07). The analysis of the mechanical quantitates for specimens with clearly distinguishable fusion of the ossification centers (26 specimens) reveled less differences between the mean values.
CONCLUSION: Load 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 be the results of an interaction between the load magnitude and bone quality.