Biomechanical comparison of PLF and PLIF with pedicle screw fixation in unstable lumbar spine

ObjectiveTo compare biomechanical effects of the posterolateral fusion (PLF) and posterior lumbar interbody fusion (PLIF) with pedicle screw fixation for various spinal instabilities. MethodsLumbar spine (L 3 -S 1 ) specimens from ten human cadavers were used. Sequential destabilization was performed at the posterior of L 4,5 and following posterior reconstruction using the pedicle screw fixation (PS) and interbody cages as follows: (1) intact and PS (IPS), (2) medial facetectomy and PS (MFPS), (3) total facetectomy and PS (TFPS), (4) partial discectomy and PS (DPS), and (5) partial discectomy and PS and interbody cages (DPSC). Biomechanical test was performed under 6 Nm flexion and extension loading modes. Construct stiffness (L 4,5 ), L 4 screw bending strain, and range of motion (ROM) of the upper adjacent level (L 3,4 ) were analyzed. Results Construct Stiffness (L 4,5 ): All reconstructions except DPS demonstrated significantly higher construct stiffness than the intact spine, and the DPSC revealed the highest stiffness among the all reconstructions. L 4 Screw Bending Strain: The DPS resulted in significantly higher strain than the other groups, and the DPSC presented statistically less strain than the other reconstructions. ROM (L 3,4 ): All reconstructions significantly increased the ROM compared to the intact. Importantly, the DPSC showed significantly greater ROM than the PS. ConclusionFor spinal instability with preserved anterior load-sharing, PLF using PS is biomechanically adequate and interbody fusion should not be performed as it further increases range of motion at the adjacent segment. However, only PS demonstrates lower spinal stiffness and higher implant strain following partial discectomy. In such cases, additional interbody cages significantly increase construct stiffness and decrease hardware strain.