Normalized vertebral-level specific range of motion corridors for female spines in rear impact.

OBJECTIVE

It is well known that the biomechanical responses of female and male spines are different in rear impacts. Female-specific finite element models are being developed as improvements over generic models. Such advancements need female-specific segmental responses for validation. The objectives of the study were to develop vertebral level-specific range of motion corridors from female human cadaver head-neck complexes exposed to rear impact loading.

METHODS

Previously conducted experiments from five human cadaver head-neck complexes were used in this analysis-based study. Briefly, the female head-neck complexes were isolated at the second thoracic vertebral level from the whole body such that the skin and the surrounding tissues of the osteoligamentous complex were intact. The distal end was fixed to the platform of a min-sled testing device. The anterior angulation of T1 was at 25 degrees with respect to the horizontal axis to simulate the normal driver posture. The occipital condyles were directly superior to the T1 body, and the Frankfort plane was horizontal. Rear impact loading were applied at a velocity of 2.6 m/s. The range of motion was defined as the inter-segmental angle at each level of the subaxial spinal column, and it was obtained by tracking the motion of the retroreflective targets that were secured on vertebral bodies and lateral masses of C2 through C7 vertebrae. Data were normalized with respect to the fifth percentile female total body mass, and corridors were developed using the equal stress equal velocity approach and expressed as mean ± 1 standard deviation corridors for each segment.

RESULTS

The segmental motions of the subaxial cervical spinal column were such that the upper regions responded with flexion while the lower regions responded with extension during the initial accelerative loading phase of the impact, resulting in a non-physiological curvature. During the later phase, all segments were in extension. individual corridors are presented as temporal responses in the body of the manuscript. A comparison of the mean temporal responses at each segment are presented to depict the angulation motion differences within the spinal column.

CONCLUSIONS

The present corridors are unique to the female spines. Because female spines have significantly (p < 0.05) different biomechanical responses when compared to male spines, local anatomical differences exist between male and female spines, and field data and clinical studies show female bias to whiplash associated disorders under the rear impact of loading, the present set of corridors serve as a fundamental dataset for the validation of female-specific finite element models. Current computational models can also use these corridors for improved validation to add confidence in their outputs.