Effects of Anterior Spinal Instrumentation on Single-Level Cervical Graft Mechanics

Anterior cervical discectomy with or without graft fusion is an acceptable surgical method for the treatment of cervical spondylosis or other spinal disc diseases. A graft-alone or graft with supplemental spinal instrumentation may be used to immobilize the operated/injured region to promote bony fusion. Graft fusion with instrumentation is intended to restore the mechanical integrity of the operated spine and decrease graft complications. Although the surgical procedure should restore the mechanical integrity of the operated spine, little is known of the load-sharing mechanics of single-level grafted constructs. We have previously shown that anterior instrumentation reverses the loading mechanics of a multi-level cervical strut-graft tested under physiologic flexion and extension conditions (DiAngelo et al., 2000). We hypothesize that a single-level anterior cervical plate will function in a similar manner. That is, a single-level anterior cervical plate will reverse the loads on the graft by loading the graft in extension and unloading the graft in flexion. We also hypothesize that a graft-alone construct does not provide adequate stabilization comparable to that of the graft-plated condition tested in flexion and extension. The objective of the study was to determine the biomechanical stability of four different spine conditions tested under physiologic flexion and extension conditions. They included the harvested, discectomized, graft-alone, and graft with single-level anterior cervical plate.