Session: 05-02-02: Injury and Damage Biomechanics II

Paper Number: 72109

Start Time: Wednesday, 01:00 PM

72109 - Neck Motions and Loads With Head Supported Mass Under Sagittal Accelerative Loading 

Introduction: The use of head supported mass has been attributed to increased incidence of spinal injuries in the military.  Any added mass to the head (helmet and head-mounted devices) changes the axial load, influences the internal load path within the osteoligamentous spinal column.  While a majority of studies in the head-neck area has been done in the automotive field, the use of head supported mass is not considered.  Objectives:  The purpose of this study was to determine the changes in the segmental motions and loads in the male and female head-neck complexes under sagittal accelerative loading.  Methods:  Our validated mid-size male head-neck finite element model was used.  The human head was integrated with a detailed cervical spinal model.  The spine consisted of the all cervical and first thoracic vertebrae, C2-T1 interertebral discs, caudal and cranial endplates, facets, ligaments, and muscles.  Cortical bones, endplates and ligaments were modeled using shell elements.  Cancellous bone, annulus, nucleus and facets were modeled using solid elements.  The neck muscles were simulated using as one-dimensional beam elements. The material properties were obtained from literature.  The mid-size female model was developed by morphing the male model using respective anatomical ratios of male and female head and cervical spines.  The helmet model was strapped to the male and female head-neck finite element models using a chinstrap that was modeled using solid elements. The models were exercised under accelerative (G_x and G_-x) by inputting accelerations in the respective directions to the T1 vertebra.  The male model simulations without helmet were validated with the human cadaver experimental data, for both accelerations.  For the former loading, segmental kinematics were compared with experimental data. The model-predicted ranges of motion were within mean±1 standard deviation corridors.  Results: The female spine responded with increased range of motions at all levels for both cases of without and with helmet; however, the maximum increase occurred in the helmeted condition. With helmet, the female model showed an increase of 11.6%, 9.4%, 11%, 10.1%, and 8.2% at C3-C4, C4-C5, C5-C6, C6-C7, and C7-T1 levels. Segmental motions with helmet were greater than without helmet. In the male model, the increases were 12.2%, 12.4%, 29.2%, 19.6% and 13.8% at C3-C4, C4-C5, C5-C6, C6-C7, and C7-T1 levels.  The increases in female model were 14.1%, 13.8%, 30.1%, 20.5% and 14.9% at the C3-C4, C4-C5, C5-C6, C6-C7, and C7-T1 levels.  Results of segmental loads will be given in the full-length paper.  Discussion/conclusions:  The segmental response in the form of the range of motion is a clinical measure for assessing the mobility of the spine, and hence, it was selected as a parameter for the assessment of gender and head supported mass. In the initial stage of the acceleration, the upper and lower spines sustained flexion and extension, resulted in a reverse curvature within the lordosis of the cervical column.  The greatest motions at the C5-C6 and C6-C7 levels were local spine curvature.  These lower spinal levels are the affected segments in clinical literature.  In the case of gender response comparison, the female spine responded with a greater segmental motion, a phenomenon observed in human cadaver studies and field data. This is attributed to the due to the differences in the morphological differences between male and female spines.  The increase in segmental motions with helmet is attributed to the center of mass shifting anteriorly and inferiorly with the added head mass.  Any increase to the in vivo head mass and shift in its center of gravity away from its natural center of rotation elevates the kinematics and may predispose to injury in females.  This study describes the role of gender and helmet on the local responses of the head-neck complex under impact acceleration. 

Presenting Author: Narayan Yoganandan Medical College of Wisconsin

Authors:

Yuvaraj Purushothaman Medical College of Wisconsin
Narayan Yoganandan Medical College of Wisconsin