| The aim of this study was to better understand the effect of adding cross-linking members to a spine instrumented with rods and pedicle screws. The general hypothesis was that the addition of the cross-link increases the mechanical stability of the spinal column, and thus allow for an increased rate of bone fusion of adjacent vertebrae. To test this hypothesis, a loading device was designed and built which subjected the spinal column to a roughly uniform moment of magnitudes up to 52 lb-in in the directions of flexion, extension, and lateral bending. A separate device was designed to apply an axial rotation to the spine, with torques up to 60 lb-in. A sample size of three (n=3) human cadaver cervical spines was tested. Each of the three cervical spine samples were tested (a) intact, (b) following a laminectomy procedure, (c) instrumented with pedicle screws and rods, (d) instrumented with one crosslink at the top of the spinal column, (e) instrumented with one crosslink at the bottom of the spinal column, and with (f) one crosslink at the top and (g) one at the bottom of the spinal column. The resulting angular displacements of the spinal column were measured with the aid of digital photography for each loading case.; According to the cadaver study, it was found that the addition of cross-linking members to a spine instrumented with rods and screws did not significantly increase the stiffness of the spine. It was also determined that there was not a significant difference between any of the instrumentation configurations. A computer analysis was also performed and showed that the addition of cross-links slightly increased the stiffness for axial rotation loads. |
