Injuries to the cervical spine incurred during emergency escape from high-performance aircraft are of concern to the Air Force. To provide for safety design, especially in view of newly cors~dered additional head encumbrances such as helmet-mounted sights and aisplays, and chemical protection equipment, a detailed dynamic structural model of the human head-spine system has been developed. The presently described effort addresses the collection of cervical spine geometric, material property and failure data for use with this model.

The specific objectives of this program were 1) to obtain stiffness and failure data for human cervical spine motion segments, and 2) to determine the necessary anthropomettic measurements of the cervical vertebrae to establish the cervical spine geometry. Six spines were obtained, radiographs of them were made and, after determining their acceptability, they were frozen until the testing protocol was ebtablished. Several testing methods were evaluated and a suitable protocol established.

The six spines were cut into motion segments and, for two specimens, a casting was made of the outer surface. Part of each vertebra was cemented in a polyester resin material. The resulting motion segment had two square, flat bases with four holes in each to attach it to one of four testing fixtures (axial, shear, bending, torsion). Each motion segment was attached individually to a particular test fixture which was itself attached to a feedback control high-strain-rate MTS testing machine. The motion segment was subjected to six different modes (one axial, two shear, two bending, one torsion) at two different strain rates (a total of 24 tests) before being failed following a prescribed protocol. The data from these tests were evaluated for strain energy loss, strain rate, and a linear spring constant, K, for each test. The specimens were refrozen after the tests.

Various methods of geometrical measurements were evaluated and a protocol was established to determine the vertebra! measuremeuts. For two of the specimens, the coordinates of points on the vertebral body were determined in a stereotaxic device and the data were manipulated in a computer so that all points were referenced to a coordinate system fixed in the vertebral body, thus allowing certain anthropometric measurements to be calculated for comparison with other published data. The second method of geometrical determination utilized a three-dimensional digitizer to obtain the same data previously obtained stereotaxically.