Biomechanical Analysis of Anterior Instrumentation for Lumbar Corpectomy

Study Design. In vitro biomechanical assessment of spinal stability after corpectomy reconstruction. Objectives. To gain a more thorough understanding of the biomechanical properties of anterior plate versus dual rod systems used for anterior lumbar corpectomy reconstruction. Summary of Background Data. Vertebral corpectomy is commonly required in the treatment of several types of spinal pathology (fracture, tumor, infection). Stabilization with strut allograft and anterior instrumentation can be accomplished with one of several anterior implant systems. These include plate systems and rod-based systems with theoretically different structural properties. Methods. Two instrumentation systems, the ATL Z-plate and the Antares system, were each applied to 10 calf lumbar spines with a cortical strut graft reconstructing an L3 corpectomy defect. All spines were tested biomechanically to determine construct stiffness under physiologic loads in multiple planes and then tested in torsion to failure. Results. There was greater stiffness (P < 0.05) in all directions of bending (flexion, extension, lateral bending) for the Antares dual rod construct compared to the Z-plate constructs. No significant difference was noted in either torsional testing under physiologic loads or torque to failure between the groups. Conclusions. Although there was significantly greater resistance to bending with the dual rod construct, the ultimate selection of a system will require an individual analysis of implant profile, construct demand, and ease of use. Both systems provided secure initial fixation following lumbar corpectomy; however, the Antares system may increase the likelihood of graft incorporation in cases with greater instability and higher load demands.