In vitro testing of the spine provides valuable information to researchers and clinicians about how neurosurgical procedures affect spinal stability and motion (Crawford, 2002). The Spinal Biomechanics Laboratory has devised several novel techniques for experimentally testing cadaveric spines, enabling researchers at our institution to study spinal biomechanics in ways that were not possible at other institutions. Many of these techniques are incorporated in the custom software developed in the Spinal Biomechanics Laboratory. This software is now used not only at Barrow, but has also been provided by Barrow for use in other biomechanics laboratories at universities in the United States.
Local Coordinate Systems
In the Spinal Biomechanics Laboratory, a technique was devised to enable each level of the spine to be tracked and studied independently (Crawford and Dickman, 1997). With this technique, the researcher points to specific vertebral landmarks with a probe in which optical markers are embedded. Custom testing software performs spatial transformations to align these landmarks with appropriate Cartesian coordinate system of the vertebra. Angular data can then be plotted in real time in individual local coordinate systems of multiple spinal levels during testing.
Three-Dimensional Spinal Angle Calculation
Publications from the Spinal Biomechanics Laboratory have contributed to the understanding of how three-dimensional (3D) joint angles are best calculated. In Crawford et al, 1996, the differences and similarities of two methods for calculating 3D joint angles, projection angles and Euler angles, were described, and a method was proposed by which the most appropriate Euler angle sequence or projection angle set can be selected for the spine and other joints of the body. In Crawford et al, 1999, a new 3D angle technique, the “tilt/twist” method, which has advantages over both the projection and Euler methods, was developed. The custom software developed in the Spinal Biomechanics Lab uses this tilt/twist method technique to display spinal angles in real time during testing.
Illustrations reprinted from Human Movement Science, 15(1), Crawford NR, Yamaguchi GT, Dickman CA: Methods for determining spinal flexion/extension, lateral bending, and axial rotation from marker coordinate data: Analysis and refinement, pg.55-78, 1996, with permission from Elsevier.