Mechanisms of cervical spine injury and coupling response with initial head rotated posture - implications for AIS coding

Objective: This objective of the present study is to describe the responses of the human head-cervical spine in terms of injuries, injury mechanisms, injury scoring, and quantify multiplanar loads. Methods: Pretest radiographs of pre-screened five human cadaver head-neck complexes were obtained. Cranium contents and sectioned the structure rostral to skull base. The caudal end was embedded, and cervical-thoracic disc was unconstrained condition. The loading was applied as a torque about the occipital condyle joint. The head and T1 were angulated 30 degrees and 25 degrees. Peak forces and moments at the occipital condyles were recorded using a six-axis load cell. After testing, x-rays and CT images were obtained. Injuries were scored using the Abbreviated Injury Scale, AIS 2015 version. Results: The mean age, stature, total body mass, body mass index of the five subjects were as follows: 63 years, 1.7 m, 78.0 kg, and 28.1 kg/m(2). The mean peak axial force and coronal, sagittal, and axial bending moments were: 754 N, and 36.8 Nm, 14.8 Nm, and 9.5 Nm. All but one specimen sustained injury. Injuries were scored at the AIS 2 level. Two specimens sustained left anterior inferior lateral mass fractures of the atlas. While the transverse atlantal ligament was intact, some capsular ligament involvement was observed. In the other two specimens, although the same injury was noted, joint diastasis of the atlas-axis joint was identified. Conclusions: Using a PMHS model, the present study described the biomechanics of the initially head rotated head-neck complex under lateral bending in terms of injuries, injury mechanisms, quantification of the multiplanar loads at the occipital condyles, and underscored potential injury scoring issues for occupant protection. The issue of diastasis is not addressed in the AIS 2015 version. While this may not always result in immediate instability and require surgical intervention, it may be necessary to revisit this issue. Upper cervical fractures with diastasis and or transverse atlantal ligament involvement may be potential injury scoring factors for AIS consideration.