Tag: Finite element analysis

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Comprehensive analysis of biomechanical stability and clinical efficacy in oblique lumbar interbody fusion with distinct anterolateral fixation modalities

J Neurosurg Spine 44:436–448, 2026

This study evaluates how different anterolateral screw angles in oblique lumbar interbody fusion with anterolateral fixation (OLIF-AF) affect cage subsidence, biomechanical stability, and clinical outcomes. A retrospective cohort of 80 L4–5 OLIF-AF patients was grouped by coronal and horizontal screw angles, supplemented by finite element models simulating four screw configurations under physiological loads.

Findings show coronal-plane parallel screw placement reduced cage subsidence, cage stress, displacement, and range of motion versus nonparallel placement, while horizontal bifurcation had no significant effect on subsidence; clinical scores and fusion rates were similar across groups. The authors recommend coronal parallelism with bicortical purchase to optimize stability and lower subsidence risk.

Coronal Plane Parallel Screw Placement: Parallel screw placement in the coronal plane during OLIF-AF significantly reduces the risk of cage subsidence (CS) and enhances biomechanical stability compared to nonparallel placement.

Nonparallel Coronal Screw Placement Risks: Nonparallel coronal screw placement (G2 and G3 groups) is independently associated with higher CS rates, greater reduction in disc height (ΔDH), increased cage stress, displacement, and range of motion (ROM), indicating poorer biomechanical outcomes.

Horizontal Screw Bifurcation: Horizontal screw bifurcation (difference in horizontal plane angle) does not have a statistically significant impact on CS risk or clinical outcomes when coronal plane parallelism is maintained.

Bicortical Purchase Importance: Ensuring that screws penetrate the contralateral vertebral cortex (bicortical purchase) may further reduce the risk of CS, while lack of penetration is associated with earlier and more severe subsidence.

Clinical Outcomes: No significant differences in pain relief (VAS-LBP, VAS-LP) or Oswestry Disability Index (ODI) were observed among the four screw configuration groups at any follow-up point; fusion rates were also similar.

Finite Element Analysis Validation: Finite element modeling confirmed that nonparallel screw configurations increase cage stress and spinal ligament tension, especially during flexion, supporting clinical findings.

Risk Factors for Subsidence: Lower bone mineral density (BMD) and nonparallel coronal screw placement are independent risk factors for cage subsidence after OLIF-AF.

Surgical Recommendation: For optimal biomechanical stability and reduced complication risk, OLIF-AF screws should be placed parallel to the coronal plane and close to the endplates, with bicortical purchase, as this configuration provides better load sharing and fusion environment.

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Effects of Sacral Slope Changes on the Intervertebral Disc and Hip Joint: A Finite Element Analysis

World Neurosurg. (2023) 176:e32-e39

Spinopelvic parameters are vital components that must be considered when treating patients with spinal disease. Several finite element (FE) studies have explored spinopelvic parameters such as sacral slope (SS) and the impact on the lumbar spine, although no study has examined the effect on the hip and sacroiliac joint (SIJ) on varying SS angles. Therefore, it is necessary to have a biomechanical understanding of the impact on the spinopelvic complex.

METHODS: An FE lumbar, pelvis, and femur model was created from computed tomography scans of a 55-year-old female patient with no abnormalities. Three models were created: a normal model (SS [ 26  ), a model with high SS (SS [ 30  ), and a model with low SS (SS [ 20  ). These models underwent loading for flexion, extension, lateral bending, and axial rotation. Range of motion (ROM), intradiscal pressures, hip joint, and SIJ contact stresses were analyzed.

RESULTS: The high SS model (SS [ 30  ) indicated the highest ROM in the L5-S1 (slip angle) level and the highest intradiscal pressures. The highest average hip and SIJ contact stresses were present in this model, although the low SS model (SS [ 20  ) in extension had the largest stresses for the hip and SIJ.

CONCLUSIONS: The results provide evidence that patients with higher SS may be more prone to increased ROM at the slip angle (L5-S1). In addition, patients with higher SS were shown to have higher contact stresses on the hip joint and SIJ, potentially leading to SIJ dysfunction. Clinically, correcting lumbar lordosis including SS is important; however, a high SS may have a negative impact on the intervertebral disc, SIJ, and hip joint.

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