Development of Spine Injury Mechanisms, Response Corridors and Computational Human Model to Assess Mounted Occupant Injury During Underbody Blast Loading

Underbody blast (UBB) is the major cause of spine trauma in battlefields today. However, the mechanical and injury responses of the human body to such events are not well understood. The purpose of this dissertation was to simulate UBB loading conditions in a laboratory setup, and to investigate mechanisms of injury and dynamic response of thoracolumbar and sacral regions. In addition, a finite element human body model was developed for UBB applications. The outline of this study is as follows:

A total of eleven whole-body instrumented cadavers were positioned supine on a seat-floor fixture attached to a decelerative horizontal sled. The sled and fixture impacted a concrete barrier mounted with pre-crushed honeycomb blocks, in order to simulate UBB loading conditions in a controlled environment. The input pulses were defined using the peak velocity and time to peak velocity for seat and floor and by the presence of body armor. Six loading conditions were tested. The responses measured included linear Z acceleration and Y angular velocity at the thoracic (T1, T5, T8, T12) and sacral (S1-S2) spine. Post-test computed tomography scans and autopsies were performed to identify the injuries.
The spinal injuries generated from this study were characterized using the Denis, 1983 and 1988 classification systems and injury severity was assessed using the AIS scoring system. The injury timing was estimated based on the spine Z acceleration and Y rotational data. Furthermore, the estimated injury timing was verified by the joint time-frequency analysis performed the spine Z acceleration data.
The underlying spinal injury mechanisms were characterized using sensor and film analysis as well as review of the literature.
The dynamic response of the spine in terms of influence of body armor and seat input pulse were evaluated. In addition, the trends among the magnitude of peak accelerations and time to peak acceleration on the spinal levels were investigated statistically. Furthermore, the relationship between the seat input pulse and the spine response was studied.
A Fast Fourier transformation was performed on the spine acceleration data, wherein amplitude spectra of the spine accelerations were analyzed, and the response spectra trends between the severity levels and between fracture vs. non-fracture cases were studied. In addition, the effect of low pass filters on the data spikes associated with spinal fracture was explored. Lastly, spine response corridors with tests performed at Wayne State University were developed.
The resulting spine response corridors were then used for modifying and validating the Global Human Body Model Consortium (GHBMC) finite element human body model for UBB applications. The modified model includes updated intervertebral discs in thoracic and spine regions. The stresses and strains generated in the spinal segments with and without fracture were analyzed.

In summary, the experimental-computational modeling approach presented in this dissertation has provided further understanding of the spine response and injury mechanisms in a simulated underbody blast environment as well as providing a potential FE design tool to help mitigate injuries.

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Year

Entry

1995

Schueler F, Mattern R, Zeidler F, Scheunert D. Injuries of the lower legs - foot, ankle joint, tibia; mechanisms, tolerance limits, injury-criteria evaluation of a recent biomechanic experiment-series (impact-tests with a pneumatic-biomechanic-impactor). In: Proceedings of the 1995 International IRCOBI Conference on the Biomechanics of Impact. September 13-15, 1995; Brunnen, Switzerland.33-45.

2004

Panjabi MM, Pearson AM, Ito S, Ivancic PC, Gimenez SE, Tominaga Y. Cervical spine ligament injury during simulated frontal impact. Spine. November 1, 2004;29(21):2395-2403.

1974

Prasad P, King AI, Ewing CL. The role of articular facets during +G_z acceleration. J Appl Mech. June 1974;41(2):321-326.

1977

Kazarian L, Graves GA Jr. Compressive strength characteristics of the human vertebral centrum. Spine. March 1977;2(1):1-14.

1999

Duma SM, Schreiber PH, McMaster JD, Crandall JR, Bass CR, Pilkey WD. Dynamic injury tolerances for long bones of the female upper extremity. J Anat. April 1999;194(3):463-471.