Biomechanical comparison of posterior cervicothoracic instrumentation techniques after one-level laminectomy and facetectomy: Laboratory investigation

Object. Posterior instrumentation is the preferred method of fixation in the unstable cervicothoracic junction (CTJ). Several posterior rod constructs of different diameters and configurations are available for instrumentation across the CTJ. The objective of this study was to compare the biomechanical stability of various posterior instrumentation techniques that cross the CTJ after a 2-column injury through the complete removal of the posterior elements at C-7. Methods. Eight fresh-frozen human cadaveric spines (C3-T4) were used. After the intact spine analysis, each specimen was destabilized (C-7 laminectomy and bilateral facetectomies) and reconstructed as follows: Group 1, C5-T2 posterior instrumentation with a 3.5-mm rod; Group 2, C5-T2 posterior instrumentation with a transitional rod (3.5-5.5 mm); and Group 3, C5-T2 posterior instrumentation with a side-to-side rod connector (3.5-5.5 mm). All reconstructed groups were tested with posterior instrumentation using the Cervifix system (Synthes, Inc.). The authors hypothesized that Group 2 would be the most stable. Results. Following laminectomy, facetectomy, and the application of instrumentation, there was a decrease in the range of motion in all treatment groups compared with the intact spine. This trend was observed in all 3 planes of motion, but was only significant on right/left lateral bending and flexion (for the transitional rod only). Although the instrumented spines were stiffer than the intact spine in right/left axial rotation, flexion, and extension, these differences did not reach statistical significance. Based on observations during testing, it was evident that in the implanted spines, most of the motion that did occur was localized at the segments adjacent to the instrumented levels. Conclusions. Based on the results of this investigation, the biomechanical stability of the transitional rod, sideto-side connector ("wedding band"), and 3.5-mm rods appears to be similar.