Biomechanical Comparison of Stand-Alone and Bilateral Pedicle Screw Fixation for Oblique Lumbar Interbody Fusion Surgery—A Finite Element Analysis

Abstract

The most common complication of oblique lumbar interbody fusion (OLIF) is endplate fracture/subsidence. The mechanics of endplate fracture in OLIF surgery are still unclear. The aim of the present study was to evaluate the biomechanical stability in patients undergoing OLIF surgery with stand-alone (SA) and bilateral pedicle screw fixation (BPSF) methods. A finite element model of the L1-L5 spinal unit was established and validated. Using the validated model technique, L4-L5 functional surgical models corresponding to the SA and BPSF methods were created. Simulations using the models were performed to investigate OLIF surgery. A 500-N compression force was applied to the superior surface of the model to represent the upper body weight, and a 7.5-Nm moment was applied to simulate the 6 movement directions of the lumbar spinal model: flexion and extension, right and left lateral bending, and right and left axial rotation. Finite element models were developed to compare the biomechanics of the SA and BPSF groups. Compared with the range of motion of the intact lumbar model, that of the SA model was decreased by 79.6% in flexion, 54.5% in extension, 57.2% in lateral bending, and 50.0% in axial rotation. The BPSF model was decreased by 86.7% in flexion, 77.3% in extension, 76.2% in lateral bending, and 75.0% in axial rotation. Compared with the BPSF model, the maximum stresses of the L4 inferior endplate and L5 superior endplate were greatly increased in the SA model. The L4 inferior endplate stress was increased to 49.7 MPa in extension, and the L5 superior endplate stress was increased to 47.7 MPa in flexion, close to the yield stress of the lamellar bone (60 MPa). OLIF surgery with BPSF could reduce the maximum stresses on the endplate, which might reduce the incidence of cage subsidence. OLIF surgery with the SA method produced more stress compared with BPSF, especially in extension and flexion, which might be a potential risk factor for cage subsidence.