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Excerpt

We would like to thank Drs. Freeman and Centeno for their interest in our research. In our biomechanical study, we quantified the dynamic strains, not loads, in the alar, transverse, and apical ligaments during head-turned rear impacts up to 8 g horizontal acceleration of the T1 vertebra. Our results indicated that the average peak dynamic ligament strains did not significantly exceed the noninjurious baseline strains and were below the failure strains of these ligaments that were extrapolated from the literature. Thus, we emphatically support our conclusions: “the alar, transverse, and apical ligaments are not at risk for injury due to head-turned rear impacts up to 8 g.”
These conclusions are based on the experimental conditions studied, as outlined in our article, and should be interpreted collectively with epidemiologic data. In a recent epidemiologic study, Kaale et al1 reported more injuries to the alar and transverse ligaments in those with rotated head posture at the time of impact, as compared with facing forward. However, in this and many other epidemiologic studies, factors such as impact acceleration, velocities at the time of the collision, single or multiple collisions, and head-vehicle contact characteristics were not published. Future biomechanical studies that investigate these factors may help elucidate the ligament injury mechanisms caused by head-turned impacts.

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