Biomechanical Impact of Cement Augmentation on Pedicle Screw Fixation and Adjacent Segment Disease in Multilevel Lumbar Fusion: A Finite Element Analysis

Abstract

Objective: Cement augmentation is widely used to enhance pedicle screw fixation, particularly in osteoporotic patients. However, its effects on adjacent segment disease (ASD) and implant failure in multilevel lumbar interbody fusion remain unclear. This study aimed to assess the effectiveness of cement augmentation in preventing implant failure and its impact on ASD risk using finite element analysis (FEA).

Methods: A FEA of L2-S1 multilevel lumbar interbody fusion was performed to evaluate the biomechanical effects of cement augmentation. Three models were analyzed under normal and osteoporotic conditions: type 1 (no augmentation), type 2 (upper instrumented vertebra [UIV] augmentation), and type 3 (UIV and UIV+1 augmentation). Range of motion (ROM), intradiscal pressure (IDP), screw pull-out risk, and implant failure were assessed.

Results: Cement augmentation significantly reduced screw pull-out risk, particularly in osteoporotic conditions, where type 1 exhibited a failure rate of 91.5%, while type 2 and type 3 remained below 39%. Cement augmentation did not demonstrate a substantial impact on ASD development, as ROM and IDP changes remained within a minimal range in this FEA model. However, osteoporosis was associated with a substantial increase in IDP, with a result as high as 809%. Despite its benefits, augmentation at UIV+1 increased the risk of pedicle screw breakage and vertebral body fracture, with L1 (UIV+1) lower endplate fracture rate of 82.7% in type 3, compared to 56.6% in type 2 and 52.8% in type 1.

Conclusion: Cement augmentation effectively improves screw fixation and does not appear to significantly increase ASD risk based on this FEA study. Limiting cement augmentation to the UIV level in lumbar multilevel fusion may help reduce the risk of implant failure, though further clinical validation is required to confirm these biomechanical findings.

Keywords: Adjacent segment disease; Cement augmentation; Finite element analysis; Implant failure; Pedicle screw fixation.

Fig. 1.

(A) Cement-augmented pedicle screw insertion at the upper instrumented vertebra (L2) and cement augmentation (vertebroplasty) at the L1 body. (B) Six types of samples. Type 1, without cement augmentation; type 2, L2 cement-augmented screws; type 3, L2 cement-augmented screws with L1 vertebroplasty.

Fig. 2.

Biomechanical analyses. (A) Screw pull-out at L2. (B) Range of motion of the L1–2 segment. (C) Intradiscal pressure at the L1–2 level. (D) Screw breakage at L2. (E) Fracture risk at L1. PVMS, peak von Mises stress.

Fig. 3.

Pull-out rates of L2 screws. Osteoporosis significantly increased the risk of screw pull-out across all stabilization types, with type 1 being the most highly affected. Type 1, without cement augmentation; type 2, L2 cement-augmented screws; type 3, L2 cement-augmented screws with L1 vertebroplasty; type 1-OP, type 1 in osteoporotic vertebra; type 2-OP, type 2 in osteoporotic vertebra; type 3-OP, type 3 in osteoporotic vertebra.

Fig. 4.

Risk of adjacent segment disease. (A) Range of motion at L1–2. (B) Intradiscal pressure at L1–2. Type 1, without cement augmentation; type 2, L2 cement-augmented screws; type 3, L2 cement-augmented screws with L1 vertebroplasty; type 1-OP, type 1 in osteoporotic vertebra; type 2-OP, type 2 in osteoporotic vertebra; type 3-OP, type 3 in osteoporotic vertebra.

Fig. 5.

Risk of implant failure. (A) Failure of L2 pedicle screws. (B) Failure of the L1 vertebral body (lower endplate). Type 1, without cement augmentation; type 2, L2 cement-augmented screws; type 3, L2 cement-augmented screws with L1 vertebroplasty; type 1-OP, type 1 in osteoporotic vertebra; type 2-OP, type 2 in osteoporotic vertebra; type 3-OP, type 3 in osteoporotic vertebra.