The Intervertebral Neck Injury Criterion (IV-NIC) is based on the hypothesis that dynamic intervertebral motion beyond physiological limits may injure soft tissues. In contrast, the Neck Injury Criterion (NIC) hypothesizes that sudden change in spinal fluid pressure may cause neural injuries. The goals of this study, using the biofidelic whole human cervical spine model with muscle force replication, were to determine the IV-NIC injury threshold due to frontal impact at each intervertebral level, and to compare the IV-NIC and NIC in determining injury. Using a bench-top apparatus, frontal impacts were simulated at 4, 6, 8, and 10 g horizontal accelerations of the T1 vertebra. Pre- and post-trauma flexibility testing measured the soft tissue injury; that is, a significant increase (p less than 0.05) in neutral zone or range of motion at any intervertebral level, above the corresponding physiological limit. Results indicated that the soft tissue injury occurred due to flexion mode of injury and its threshold was 8 g. The average IV-NIC injury threshold (95% confidence interval) was 2.0 (1.2-2.8) at C4-C5 and 2.3 (1.6-3.0) at C6-C7, while the average NIC injury threshold was 18.4 (17.9-19.0) m2/s2. The NIC injury threshold was reached significantly earlier than all the IV-NIC injury thresholds, demonstrating that the NIC may be unable to predict facet and soft tissue injury caused by non-physiologic inververtebral rotation. Present results suggest that IV-NIC is an effective tool for determining soft tissue neck injuries by identifying the intervertebral level, mode, time, and severity of injury. (Author/publisher).
Abstract