Biomechanical comparison between cortical screw-rod construct versus pedicle screw-rod construct in transforaminal lumbar interbody fusion

OBJECTIVE: To compare construct stiffness of cortical screw (CS)-rod transforaminal lumbar interbody fusion (TLIF) construct (G2) versus pedicle screw (PS)-rod TLIF construct (G1) in the standardized porcine lumbar spine. METHODS: Six porcine lumbar spines (L2-L5) were separated into 12 functional spine units. Bilateral total facetectomies and interlaminar decompression were performed for all specimens. Non-destructive loading to assess stiffness in lateral bending, flexion and extension as well as axial rotation was performed using a universal material testing machine. RESULTS: PS and CS constructs were significantly stiffer than the intact spine except in axial rotation. Using the normalized ratio to the intact spine, there is no significant difference between the stiffness of PS and CS: flexion (1.41 ± 0.27, 1.55 ± 0.32), extension (1.98 ± 0.49, 2.25 ± 0.44), right lateral flexion (1.93 ± 0.57, 1.55 ± 0.30), left lateral flexion (2.00 ± 0.73, 2.16 ± 0.20), right axial rotation (0.99 ± 0.21, 0.83 ± 0.26) and left axial rotation (0.96 ± 0.22, 0.92 ± 0.25). CONCLUSION: The CS-rod TLIF construct provided comparable construct stiffness to a traditional PS-rod TLIF construct in a 'standardized' porcine lumbar spine model