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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