Biomechanical comparison of posterior lumbar interbody fusion cages.

Study Design: Cadaveric human and bovine lumbar spine models simulating the acute postoperative period were used to compare the biomechanical properties of two designs of intervertebral body threaded fusion cages. The instrumented spines were compared with intact spines and with spines with resected posterior elements, representing a revision case.
Objective: To determine the relative biomechanical performance of these competing devices.
Summary of Background Data: These cages are currently under clinical investigation, and basic biomechanical data are needed.
Methods: Insertion torques and maximum pushout loads were measured for each cage. Intact spines, posteriorly instrumented spines (posterior lumbar interbody fusion), and spines with resected posterior elements were loaded in axial compression, flexion and extension bending, and axial torsion. Stiffness comparisons were made between the different configurations.
Results: Insertion torques and pushout loads were similar for the cages. Both cages significantly increased stiffnesses above those of the intact spines and the resected spines. The BAK-instrumented spines were more stiff in axial compression, while the Threaded Interbody Fusion Device spines were more stiff in extension.
Conclusions: This study revealed the two cages to have similar biomechanical characteristics immediately after posterior insertion and warrant further clinical studies.