Cervical Posterior Fusion Rods Undergo Substantial Bending Deformations for Activities of Daily Living

Cervical corpectomy is a procedure most commonly indicated for resection of metastatic disease in the vertebra, access to the spinal cord tumors and inflammatory or infectious lesions.[1] Posterior occipitocervical instrumentation with rods and lateral mass screws has been shown to be a rigid fixation technique in this region [2] and, small diameter rods are thought to be lighter weight, less prominent and less likely to be associated with screw pullout.[3] Still, deformity imposed upon small diameter rods, by the weight of the head, the cervical spine, and spinal ligaments has yet to be quantified. Anecdotal observations show that the rods lose their lordotic curvature and patients fuse in a kyphotic curve making daily living more difficult. The goal of this study is to examine the mechanical behavior of these rods in situ under physiologic loading conditions reflective of activies of daily living.