Neurological, functional, and biomechanical characteristics after high-velocity behind armor blunt trauma of the spine.

Background: Behind armor blunt trauma (BABT) describes a nonpenetrating injury to the organs of an individual wearing body armor. The aim of this study was to investigate the neurologic and functional changes that occur in the central nervous system after high-velocity BABT of the spine as well as its biomechanical characteristics.

Methods: This study evaluated 28 healthy adult white pigs. Animals were randomly divided into three experimental groups: (1) 15 animals (9 in the exposed group and 6 in the control group) were tested for neurologic changes; (2) 10 animals (5 in the exposed group and 5 in the control group) were used for studies of cognitive function; (3) and 3 animals were used for examination of biomechanics. In the group tested for neurologic changes, 9 anesthetized pigs wearing body armor (including a ceramic plate and polyethylene body armor) on the back were shot on the eighth thoracic vertebrae (T8) with a 5.56-mm rifle bullet (velocity appropriately 910 m/s). As a control, six pigs were shot with blank ammunition. Ultrastructural changes of the spinal cord and brain tissue were observed with light and electron microscopy. Expression levels of myelin basic protein, neuron-specific enolase (NSE), and glial cytoplasmic protein (S-100B) were investigated in the serum and cerebrospinal fluid using enzyme-linked immunosorbent assays. Electroencephalograms (EEGs) were monitored before and 10 minutes after the shot. Pressures in the spine, common carotid artery, and brain were detected. Acceleration of the 10th vertebrae (T10) was tested. Finally, cognitive outcomes between exposed and control groups were compared.

Results: Neuronal degeneration and nerve fiber demyelination were seen in the spinal cord. The concentrations of neuron-specific enolase, myelin basic protein, and S-100B were significantly increased in the serum and cerebrospinal fluid 3 hours after trauma (p < 0.05). The electroencephalogram was suppressed within 3 to 6 minutes after trauma. The pressure detected in the brain was higher than that detected in the common carotid artery (p < 0.01). The trauma resulted in paralysis of two hind limbs and in cognitive dysfunction.

Conclusion: The results from our animal model indicate that high-velocity BABT of the spine generates high pressure and acceleration in the spine, induces varying degrees of paralysis of hind limbs, and disturbs cerebral function. The neuronal degeneration caused by the pressure wave may be one of the important pathologic events involved in the development of trauma-related complications.