Frontal impact causes ligamentous cervical spine injury

Study Design. Whole cervical spine model with muscle force replication was subjected to simulated frontal impacts of increasing severity, and resulting injuries were evaluated via flexibility testing. Objectives. To identify and quantify cervical spine soft tissue injury and the injury threshold acceleration due to frontal impact. Summary of Background Data. Cervical spine instability may result from automotive collisions. No previous studies have quantified soft tissue injuries due to frontal impact. Methods. Six human cervical specimens (occiput-T1) with muscle force replication were subjected to frontal impacts of 4, 6, 8, and 10 g. Before frontal impact, baseline flexibility data were collected following a 2 g simulation. Flexibility parameters of total (flexion plus extension) neutral zone (NZ), flexion NZ, total range of motion (ROM), and flexion ROM were obtained following each impact and compared with baseline flexibility. Injury was a significant increase (P < 0.05) in intervertebral flexibility due to frontal impact over baseline. Injury threshold was the lowest T1 peak acceleration that caused injury. Results. The injury threshold acceleration was 8 g, as determined by significant increases of 12.6 to 51.4% over the baseline flexibility, in the C4-C5 total NZ, and the C6-C7 total NZ, flexion NZ, total ROM, and flexion ROM. Following 10 g, significant increases in flexibility parameters were observed at C2-C3, C3-C4, C4-C5, C6-C7, and C7-T1. Conclusions. Middle (C2-C3 to C4-C5) and lower (C6-C7 and C7-T1) cervical spine were at risk for injury during frontal impacts, for the experimental conditions studied.