Biomechanical Analysis of Double-Level Oblique Lumbar Fusion with Different Types of Fixation: A Finite Element-Based Study

Abstract

Objective: One well-liked less invasive procedure is oblique lumbar interbody fusion (OLIF). The biomechanical characteristics of double-level oblique lumbar interbody fusion in conjunction with various internal fixations are poorly understood. The purpose of this study was to clarify the biomechanical characteristics of double-level oblique lumbar interbody fusion for osteoporosis spines using various internal fixation techniques.

Methods: Based on CT scans of healthy male volunteers, a complete finite element model of osteoporosis in L1-S1 was established. After validation, L3-L5 was selected as the surgical segment to construct four surgical models: (a) two stand-alone cages (SA); (b) two cages with unilateral pedicle screws (UPS); (c) two cages with bilateral pedicle screws (BPS); and (d) two cages with bilateral cortical bone trajectory screws (CBT). Segmental range of motion (ROM), cage stress, and internal fixation stress were studied in all surgical models and compared with the intact osteoporosis model.

Results: The SA model had a minimal reduction in all motions. The CBT model had the most noticeable reduction in flexion and extension activities, while the reduction in the BPS model was slightly less than that in the CBT model but larger than that in the UPS model. The BPS model had the greatest limitation in left-right bending and rotation, which was greater than the UPS and CBT models. CBT had the smallest limitation in left-right rotation. The cage stress of the SA model was the highest. The cage stress in the BPS model was the lowest. Compared with the UPS model, the cage stress in the CBT model was larger in terms of flexion and LB and LR but slightly smaller in terms of RB and RR. In the extension, the cage stress in the CBT model is significantly smaller than in the UPS model. The CBT internal fixation was subjected to the highest stress of all motions. The BPS group had the lowest internal fixation stress in all motions.

Conclusions: Supplemental internal fixation can improve segmental stability and lessen cage stress in double-level OLIF surgery. In limiting segmental mobility and lowering the stress of cage and internal fixation, BPS outperformed UPS and CBT.

Keywords: Biomechanical; Cortical Bone Trajectory Screw; Finite Element Analysis; Oblique Lumbar Interbody Fusion; Osteoporosis; Posterior Pedicle Screw.

Fig. 1

Various finite element models: (A) intact osteoporosis model, (B) two stand‐alone cages, (C) two cages with unilateral pedicle screws, (D) two cages with bilateral pedicle screws, and (E) two cages with bilateral cortical bone trajectory screws

Fig. 2

Comparison of the ROM between the normal intact model and the previous in vitro experimental study. LB: left bending; RB: right bending; LR: left rotation; RR: right rotation; ROM: range of motion

Fig. 3

The ROM of segment (L3–L5). Intact: intact osteoporosis model; SA: stand‐alone cage; UPS: cage with unilateral pedicle screws; BPS: cage with bilateral pedicle screws; CBT: cage with bilateral cortical bone trajectory screws; LB: left bending; RB: right bending; LR: left rotation; RR: right rotation; ROM: range of motion

Fig. 4

Stress on cage (L3–L5). SA: stand‐alone cage; UPS: cage with unilateral pedicle screws; BPS: cage with bilateral pedicle screws; CBT: cage with bilateral cortical bone trajectory screws; LB: left bending; RB: right bending; LR: left rotation; RR: right rotation

Fig. 5

Cage stress distribution was observed in four groups of surgical models during all motions. Pictures of each group of models from top to bottom are flexion, extension, left rotation, right rotation, left bending, and right bending. UPS: cage with unilateral pedicle screws; BPS: cage with bilateral pedicle screws; CBT: cage with bilateral cortical bone trajectory screws

Fig. 6

Stress of internal fixation devices. UPS: cage with unilateral pedicle screws; BPS: cage with bilateral pedicle screws; CBT: cage with bilateral cortical bone trajectory screws; LB: left bending; RB: right bending; LR: left rotation; RR: right rotation

Fig. 7

Stress distribution of internal fixation devices. The models of all internal fixation groups from top to bottom are flexion, extension, left rotation, right rotation, left bending, and right bending. UPS: cage with unilateral pedicle screws; BPS: cage with bilateral pedicle screws; CBT: cage with bilateral cortical bone trajectory screws