Impact of a novel patient-specific, patient-matched Bezier parametric curve rod platform on proximal junction biomechanics in an in silico thoracolumbar instrumented fusion model.

Authors

Franck Le Naveaux, Bahe Hachem, Sasha Vaziri, Varun Puvanesarajah, Saeed Sadrameli, David O Okonkwo, Thomas J Buell, Amit Jain, Hamid Hassanzadeh, Craig Forsthoefel, Reginald Fayssoux, Zachary J Tempel, Alekos A Theologis, Christopher S Ahuja

Published in

Spine deformity. Jul 11, 2025. Epub Jul 11, 2025.

Abstract

To evaluate the biomechanical performance of a novel Bezier surface-smoothed transition rod, and to compare it to conventional and stepped rods, focusing on correction capability, spinal stabilization, instrumentation and spinal loading related to risk of proximal junctional kyphosis (PJK).
A spine finite element model with patient-specific 3D spinal geometry (severe sagittal imbalance from thoracolumbar kyphosis) was used. Surgical instrumentation with five rod types was simulated: (1) constant 6.0 mm diameter, (2) stepped 6.0 mm-5.0 mm diameter, (3) Bezier 6.0 mm-5.5 mm-5.0 mm diameter, (4) constant 5.5 mm diameter, and (5) Bezier 5.5 mm-5.0 mm-4.75 mm diameter. Gravitational forces and flexion movements were simulated to compare load transfer between the spine and instrumentation.
All rod configurations achieved equivalent sagittal correction. Load distribution analysis showed that Bezier rods provided smoother load transitions and better offloading of proximal segments compared to constant diameter rods. The highest moment sustained by the segment adjacent to the instrumentation was observed with the constant 6 mm rod (9N.m), while the Bezier 5.5-5-4.75 mm rod showed the lowest moment (7.5Nm), indicating reduced stress of 16% on the upper adjacent vertebrae. Similarly, the Bezier rods were more effective in offloading pedicle screws up to 45% with respect to the stiffer rod construct, potentially reducing the risk of PJK.
The simulation analysis demonstrates Bezier rods offer promising biomechanical benefits particularly in load distribution and stress reduction at adjacent levels of long thoracolumbar instrumentation. Future efforts will focus on clinical validation and optimization of patient-specific designs.

PMID:
40643818
Bibliographic data and abstract were imported from PubMed on 11 Jul 2025.

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