Complex Neck Loading and Injury Tolerance in Lateral Bending With Head Rotation From Human Cadaver Tests

Advancements in automated vehicles may position the occupant in postures different from the current standard posture. It may affect human tolerance responses. The objective of this study was to determine the lateral bending tolerance of the head-cervical spine with initial head rotation posture using loads at the occipital condyles and lower neck and describe injuries. Using a custom loading device, head-cervical spine complexes from human cadavers were prepared with load cells at the ends. Lateral bending loads were applied to prerotated specimens at 1.5 m/s. At the occipital condyles, peak axial and antero-posterior and medial-lateral shear forces were: 316-954 N, 176-254 N, and 327-508 N, and coronal, sagittal, and axial moments were: 27-38 N·m, 21-38 N·m, and 9.7-19.8 N·m, respectively. At the lower neck, peak axial and shear forces were: 677-1004 N, 115-227 N, and 178-350 N, and coronal, sagittal, and axial moments were: 30-39 N·m, 7.6-21.3 N·m, and 5.7-13.4 N·m, respectively. Ipsilateral atlas lateral mass fractures occurred in four out of five specimens with varying joint diastasis and capsular ligament involvements. Acknowledging that the study used a small sample size, initial tolerances at the occipital condyles and lower neck were estimated using survival analysis. Injury patterns with posture variations are discussed.

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/m². 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.