Biomechanical Impact of Splint Rods in Posterior Cervicothoracic Fixation: A Finite Element Analysis

Area of Science:

• Spine biomechanics
• Orthopedic implant technology
• Finite element analysis in surgery

Background:

• Cervicothoracic fixation is crucial for spinal stability after C7 vertebrectomy.
• Understanding biomechanical factors influencing construct load-bearing capacity is essential for surgical success.

Purpose of the Study:

• To investigate the impact of splint rods, rod material, and rod diameter on cervicothoracic construct load-bearing capacity.
• To identify optimal configurations for enhanced spinal fixation stability.

Main Methods:

• Finite element analysis simulated 8 construct variations in a C7 vertebrectomy model (C5-T2 pedicle screw fixation).
• Variations included rod material (titanium vs. cobalt-chrome), splint rods (presence/absence, 3.5/4.5 mm diameter), and screw sizes (3.5/4.0 mm).
• Boundary conditions followed ASTM F1717/ISO 12189 standards, analyzing yield load, displacement, stiffness, and stress.

Main Results:

• The optimal configuration (3.5 mm titanium primary and splint rods) yielded the highest load capacity (107N) and stiffness (29.8 N/mm).
• The least effective configuration (single 3.5 mm titanium rod) showed the lowest load capacity (66N).
• Increased stiffness via larger diameters or cobalt chrome alloy did not consistently improve load-bearing capacity, risking bone-screw interface failure.

Conclusions:

• Splint rods demonstrably improve the load-bearing capacity of cervicothoracic fixation constructs.
• Achieving optimal construct performance requires balancing stiffness with load-sharing to prevent premature failure at the bone-screw interface.