Biomechanical Comparison of Anterior versus Transverse Threaded Fusion Cages

Jason A. Heth, MD
Patrick W. Hitchon, MD
Vijay K. Goel, PhD
Thomas N. Rogge, MS (Iowa City, IA)

Introduction:

Lumbar interbody fusion can be used to treat degenerative spinal instability. Posterior and anterior approaches are commonly used, however both require longitudinal ligament removal and risk injury to adjacent structures. Transverse application of interbody cages has been increasingly utilized. Benefits of this approach include preservation of the longitudinal ligaments, greater cage engagement with the vertebral bodies, and avoidance of critical structures. This study compares the biomechanics of fusion cages placed via an anterior or lateral approach.

Methods:

Six ligamentous cadaveric spines were mounted on a biomechanical testing frame. Instability was produced by either an anterior or lateral discectomy at L4–L5. Either bilateral anterior or single lateral Ray cages were implanted. Biomechanical testing was performed on the intact specimen, after discectomy, and after cage implantation. Angular rotation data was generated by the Selspot II system. Motion was assessed in flexion, extension, lateral bending, and axial rotation.

Results:

Discectomy resulted in increased motion in all directions in both approaches. Anterior cage and lateral cage placements both resulted in spinal motion similar to the intact state (P>0.05). The difference between the anteriorly and laterally instrumented spines is not significantly different(P>0.05).

Discussion/Conclusions:

Anterior and lateral lumbar cages placed through an result in angular motion which is similar to the intact spine. Further, the laterally placed cages are biomechanically similar to cages placed anteriorly. The advantages of the lateral cages combined with biomechanics similar to existing cage placements makes the lateral approach an attractive alternative in lumbar fusion.