Introduction: The biomechanical feasibility of stand-alone lateral plating is being investigated as an alternative to bilateral pedicle screw (BPS) fixation in patients undergoing lateral lumbar interbody fusion (LLIF). Here, we present a biomechanical analysis of LLIF with lateral versus posterior fixation on range-of-motion (ROM) in various conditions, including after construct fatigue±instability. Methods: Fifteen cadaveric functional spine units (FSUs) were divided between two-screw lateral plate (LP), four-screw LP, or BPS after LLIF. ROM was measured using a six-degree-of-freedom motion simulator and motion tracking software to analyze flexion/extension (FE), lateral bending (LB), and axial rotation (AR) in the following conditions: intact, post-operative, post-fatigue, post-instability through pars fracture, and post-instability with fatigue. Fatigue was simulated through 1000 loading cycles in each bending plane at 1.0 Hz. Relevant statistical analysis was performed with significance set at P <0.05. Results: Specimen characteristics were similar between groups ( P =0.216). Compared with intact, post-operative ROM was significantly decreased (FE: P =0.001; LB: P <0.001; AR: P <0.001). There were no intergroup differences when comparing across fixation (FE: P =0.142; LB: P =0.112; AR: P =0.089). In fatigue simulation, all groups had increased ROM following the first fatigue; however, increased motion was insignificant (FE: P =0.075; LB: P =0.316; AR: P =0.178). Specimens experienced increased AR ( P =0.001) and LB ( P =0.015) after fatiguing the pars fracture when compared with post-fatigue ROM. Two-screw LP exhibited the most instability in this condition (FE: +29.5%, LB: +10.7%, AR: +48.9%). Fatigue effect was reduced in the BPS group ( vs. two-screw LP—FE: −19.0%, LB: −5.7%, AR: −23.6%; vs. four-screw LP—FE: −4.7%, LB: −0.34%, AR: −7.7%), though significance was not achieved. Conclusions: No statistical differences between four-screw LP and BPS were noted in any condition. During fatigue stress±instability, ROM increased in all groups, though to a lesser extent in BPS. In the absence of significant anatomic instability, four-screw LP may provide similar biomechanical rigidity compared with BPS. Further testing is warranted.
Shah et al. (Mon,) studied this question.