Biomechanical effects of different bone conditions on oblique lumbar interbody fusion augmented with various fixation options: a finite element analysis.

OBJECTIVE

The purpose of this study was to analyze the biomechanical properties of oblique lumbar interbody fusion (OLIF) combined with various fixation methods under different bone conditions (normal bone, osteopenia and osteoporosis).

METHODS

The L3-L5 finite element (FE) models of normal bone (NB), osteopenia (OS) and osteoporosis (OP) were constructed. The OLIF combined with four kinds of internal fixation surgery models were constructed: OLIF Stand-alone (SA) ; OLIF + lateral plate fixation (OLIF + LP) ; OLIF + unilateral pedicle screw fixation (OLIF + UPS) ; OLIF + bilateral pedicle screw fixation (OLIF + BPS). A load of 500 N and a torque of 7.5 Nm were applied to the upper surface of L3 to simulate flexion (FL), extension (EX), left bending (LB), right bending (RB), left rotation (LR) and right rotation (RR). The range of motion (ROM) of the model, the maximum stress of Cage, L5 upper endplate and internal fixation were recorded.

RESULTS

(1) ROM comparison: Compared with the intact model, SA ROM decreased the least, BPS decreased the most, LP decreased significantly in the LB and RB, and was less stable in the FL and EX. (2) Stress comparison: the stress of SA endplate is the largest, the stress of BPS is the smallest, and the stress of LP is lower than that of UPS in LB and RB. The Cage stress is lower than its yield strength. The fixation stress of LP was roughly the same as that of BPS in LB and RB. In the NB and OS models, the fixation stress of LP under FL exceeds the minimum fatigue strength of the material by 22.72% and 33.78%, respectively. In the OP, the fixation stress exceeds the minimum fatigue strength of the material at FL and EX, and reaches 53.25% (>50%) at FL.

CONCLUSION

OLIF supplemented with internal fixation can improve segment stability, and BPS is superior to UPS and LP fixation in limiting segment ROM and reducing stress. Under OP, the LP fixation stress at FL and EX exceeds the minimum fatigue strength of the material, which may increase the risk of fracture and internal fixation failure.