Biomechanical study of oblique lumbar interbody fusion (OLIF) augmented with different types of instrumentation: a finite element analysis

Abstract

Background: To explore the biomechanical differences in oblique lumbar interbody fusion (OLIF) augmented by different types of instrumentation.

Methods: A three-dimensional nonlinear finite element (FE) model of an intact L3-S1 lumbar spine was built and validated. The intact model was modified to develop five OLIF surgery models (Stand-alone OLIF; OLIF with lateral plate fixation [OLIF + LPF]; OLIF with unilateral pedicle screws fixation [OLIF + UPSF]; OLIF with bilateral pedicle screws fixation [OLIF + BPSF]; OLIF with translaminar facet joint fixation + unilateral pedicle screws fixation [OLIF + TFJF + UPSF]) in which the surgical segment was L4-L5. Under a follower load of 500 N, a 7.5-Nm moment was applied to all lumbar spine models to calculate the range of motion (ROM), equivalent stress peak of fixation instruments (ESPFI), equivalent stress peak of cage (ESPC), equivalent stress peak of cortical endplate (ESPCE), and equivalent stress average value of cancellous bone (ESAVCB).

Results: Compared with the intact model, the ROM of the L4-L5 segment in each OLIF surgery model decreased by > 80%. The ROM values of adjacent segments were not significantly different. The ESPFI, ESPC, and ESPCE values of the OLIF + BPSF model were smaller than those of the other OLIF surgery models. The ESAVCB value of the normal lumbar model was less than the ESAVCB values of all OLIF surgical models. In most postures, the ESPFI, ESPCE, and ESAVCB values of the OLIF + LPF model were the largest. The ESPC was higher in the Stand-alone OLIF model than in the other OLIF models. The stresses of several important components of the OLIF + UPSF and OLIF + TFJF + UPSF models were between those of the OLIF + LPF and OLIF + BPSF models.

Conclusions: Our biomechanical FE analysis indicated the greater ability of OLIF + BPSF to retain lumbar stability, resist cage subsidence, and maintain disc height. Therefore, in the augmentation of OLIF, bilateral pedicle screws fixation may be the best approach.

Keywords: Augmentation; Biomechanical study; Finite element analysis; Lumbar spine; Oblique lumbar interbody fusion.

Fig. 1

A three-dimensional nonlinear finite element (FE) model of the intact lumbar spine (L3–S1)

Fig. 2

FE models of the lumbar spine (L3–S1). a Intact model, b Stand-alone oblique lumbar interbody fusion (OLIF), c OLIF with lateral plate fixation (OLIF + LPF), d OLIF with unilateral pedicle screws fixation (OLIF + UPSF), e OLIF with bilateral pedicle screws fixation (OLIF + BPSF), f OLIF with translaminar facet joint fixation and unilateral pedicle screws fixation (OLIF + TFJF + UPSF)

Fig. 3

A view of the cage a and b lateral plate, c bilateral pedicle screws, and d translaminar facet joint + unilateral pedicle screws fixation instruments

Fig. 4

The sizes of the pedicle screws and lateral endplate. a Front distances of two upper pedicle screws or two lower pedicle screws; b rear distances of two upper pedicle screws; c front distance of an upper and a lower pedicle screw; d rear distance of an upper and a lower pedicle screw; e distances of two upper or two lower screws; f distance of the upper and lower pedicle screws

Fig. 5

Calibration results of five major ligaments in a model of the intact lumbar spine. PLL posterior longitudinal ligament, CL capsule ligament, ISL interspinous ligament, SSL supraspinal ligament, FL flavum ligament

Fig. 6

In-vitro and finite element segmental motion values during flexion–extension, lateral bending, axial rotation and compression

Fig. 7

The range of motion at the L3–L4 and L5–S1 segments as obtained with six models and six different postures. a L3–L4 segment, b L5–S1 segment

Fig. 8

The range of motion (ROM) at the L4–L5 segment and the percentage changes in this segment compared with the intact model for six different postures. a L4–L5 segment ROM, b Data on the L4–L5 segment ROM, c L4–L5 segment-percentage

Fig. 9

Equivalent stress peak of the fixation instruments as determined in four OLIF models (OLIF + LPF, OLIF + UPSF, OLIF + BPSF and OLIF + TFJF + UPSF) and for six postures

Fig. 10

Equivalent stress peak of the cage as determined in five OLIF models (Stand-alone OLF, OLIF + LPF, OLIF + UPSF, OLIF + BPSF and OLIF + TFJF + UPSF) and for six postures

Fig. 11

Equivalent stress peak of the cortical endplate as determined in the intact model and in five OLIF models (Stand-alone OLF, OLIF + LPF, OLIF + UPSF, OLIF + BPSF, and OLIF + TFJF + UPSF) for six postures

Fig. 12

Equivalent stress average value of cancellous bone as determined in the intact model and in five OLIF models (Stand-alone OLF, OLIF + LPF, OLIF + UPSF, OLIF + BPSF and OLIF + TFJF + UPSF) for six postures