Reconstruction after multilevel corpectomy in the cervical spine. A sagittal plane biomechanical study

STUDY DESIGN An in vitro biomechanical study of reconstruction techniques used after multilevel cervical corpectomy. OBJECTIVES To determine the biomechanical behavior of the cervical spine after a multilevel corpectomy and reconstruction with a strut graft and supplementation of the graft with anterior and posterior plates. SUMMARY OF BACKGROUND DATA Reconstruction of the spine after multilevel corpectomy represents a significant challenge, with nonunion or graft dislodgment being relatively common. Anterior and posterior plate fixation have increased the possibilities for supplemental stabilization. Although some clinical studies have been performed to examine multilevel corpectomies reconstructed with plates, biomechanical studies are few and are limited to single-segment models. METHODS Flexibility testing was performed on 11 intact cervical spine preparations. Flexibility testing was also conducted on the spine preparations after reconstruction with a strut graft, after supplementation of the graft with an anterior plate, and after supplementation of the graft with lateral mass plates. Physiologic moments were applied dynamically, and the three-dimensional motion of the specimen was recorded with stereophoto-grammetry. Failure testing was performed on the plated specimens in compression. Load displacement curves and failure modes were analyzed. RESULTS The range of motion after reconstruction compared with the control was decreased 24% after strut grafting, 43% after application of an anterior plate, and 62% after application of posterior plates. Similarly, flexibility coefficients showed that the posterior plate technique was the least flexible, followed by the anterior plate technique, with the graft alone being the most flexible reconstruction construct. Load to initial failure tended to be higher in posterior than in anterior plate specimens, and screw pullout was the predominant failure mode. CONCLUSIONS The application of plates to the cervical spine as an adjunct to bone graft may improve the surgeon's ability to stabilize the spine after multilevel corpectomy. Understanding the biomechanics of these devices and the potential mode of failure is important in their use.