Biomechanical effects of a titanium intervertebral cage as a stand-alone device, and in combination with locking plates in the canine caudal cervical spine

Objective: To evaluate the change in ex vivo biomechanical properties of the canine cervical spine, due to an intervertebral cage, both as a stand-alone device and in combination with plates. Study Design: Experimental ex vivo study. Animals: Cervical spinal segments (C5-C7) from eight canine cadavers. Methods: The range of motion (ROM) and elastic zone stiffness (EZS) of the spines were determined with a four-point bending device in flexion/extension, lateral bending, and axial rotation for four conditions: native, discectomy, cage (at C6-C7), and cage with plates (at C6-C7). The disc height index (DHI) for each condition was determined using radiography. Results: Discectomy resulted in overall increased ROM (p <.01) and EZS (p <.05) and decreased DHI (p <.005) when compared to the native condition. Placement of the cage increased DHI (p <.001) and restored total ROM during flexion/extension, lateral bending and axial rotation, and EZS during flexion/extension to the level of the native spine. Application of the plates further reduced the total ROM during flexion/extension (p <.001) and lateral bending (p <.001), but restored ROM in extension and EZS during lateral bending. No implant failure, subsidence, or significant cage migration occurred during loading. Conclusion: An anchorless intervertebral cage used as a stand-alone device was able to restore the disc height and spinal stability to the level of the native cervical spine, whereas the addition of plates further reduced the spinal unit mobility. Clinical Significance: This study implies that the intervertebral cage may be used as a stand-alone device in the spinal unit fixation in the canine cervical spine.