In vitro mechanical testing and finite element analysis of a novel β-Titanium alloy pedicle screw-rod fixation system

doi:10.12122/j.issn.1673-4254.2026.03.17

Abstract

Abstract:

Objective To compare the biomechanical properties of a novel Ti-3Zr-2Sn-3Mo-25Nb β‑titanium alloy and a traditional Ti-6Al-4V titanium alloy pedicle screw-rod fixation system in posterior lumbar interbody fusion (PLIF). Methods In vitro mechanical tests were conducted to evaluate the bending, tensile, compressive, and torsional performance of the β-titanium alloy screws, connecting rods, and the assembled screw-rod fixation system. Two PLIF finite element models were constructed to compare the effects of Ti-6Al-4V versus β-titanium screw-rod systems on range of motion (ROM) and stresses in the endplate and implants. Results In vitro tests showed that the β‑titanium alloy screw exhibited good resistance to bending (455.95±18.66 N) and torsion (9.03±0.20 N·m). The maximum tensile load of the β-titanium rod was 17 647.06±101.89 N, and the β-titanium screw‑rod system showed a maximum compressive load of 417.65±5.09 N and a maximum torque of 25.00±0.70 N·m. Compared with Ti-6Al-4V, the β‑titanium model showed a 2.6%-8.3% increase in ROM, and the peak stresses in the interbody bone graft, cage, and endplate increased by 1.4%-8.5%, 2.2%-9.4%, and 2.2%-10.1%, respectively, whereas the peak stresses at the bone-screw interface and within the screw-rod system decreased by 8.8%-23.7% and 19.0%-33.1%, respectively. Conclusion The β‑titanium pedicle screw-rod fixation system exhibits good in vitro mechanical performance to provide stability comparable to the conventional Ti-6Al-4V system while markedly reducing stress concentration within the screw-rod construct, suggesting its great potential for clinical application.

Key words: β-titanium alloy, pedicle screw-rod fixation system, finite element analysis, posterior lumbar interbody fusion

Jie LI, Yinan LIU, Dong WANG, Haopeng LI, Xijing HE, Teng LU. In vitro mechanical testing and finite element analysis of a novel β-Titanium alloy pedicle screw-rod fixation system[J]. Journal of Southern Medical University, 2026, 46(3): 638-645.

Figures/Tables 8

Fig.1 Finished β-Titanium alloy screws and the connecting rods.

Fig.2 Static mechanical testing of β-titanium alloy screws and rods. A: Tensile test of the β-titanium alloy rod. B: Compression-torsion test of the β-titanium alloy screw-rod system. C: Torsion test of the β-titanium alloy screw. D: Bending test of the β-titanium alloy screw.

Fig.3 Intact L4-L5 lumbar finite element model. A: Lateral view. B: Posterior view. C: Axial view.

Tab.1 Material properties and element types in the finite element models

Materials	Element type	Constitutive equation	Young's modulus	Poisson's ratio (μ)
Cortical bone	C3D4	Isotropic elastic	12 GPa	0.3
Cancellous bone	C3D4	neo-Hookean	C₁₀ = 19.38 MPa, D = 0.0252 MPa
Bony endplate	C3D8I	Isotropic elastic	1.2 GPa	0.29
Cartilage endplate	C3D8I	neo-Hookean	C₁₀ = 4.10 MPa, D =0.03 MPa
Nucleus pulposus	C3D8H	Mooney-Rivlin	C₁₀ = 0.12 MPa, C₀₁ = 0.03 MPa
Annulus ground	C3D8H	Mooney-Rivlin	C₁₀ = 0.18 MPa, C₀₁ = 0.045 MPa
Annulus fiber	T3D2	Hypoelastic	360-550 MPa
Screws and rods	C3D4	Isotropic elastic	110 GPa, 55 GPa	0.3
Cage	C3D4	Isotropic elastic	3.6 GPa	0.25
Bone grafts	C3D4	Isotropic elastic	100 MPa	0.2

Fig.4 Posterior lumbar interbody fusion (PLIF) model. A: Lateral view. B: Posterior view. C: Axial view.

Fig.5 Results of in vitro mechanical testing of the β-titanium alloy pedicle screw-rod fixation system. A: Torsion test of the β‑titanium alloy screw. B: Bending test of the β‑titanium alloy screw. C: Tensile test of the β‑titanium alloy rod. D: Compression test of the β-titanium alloy screw-rod fixation system. E: Torsion test of the β‑titanium alloy screw-rod fixation system.

Fig.6 Results of segmental range of motion and stress within components. A: Segment range of motion for each model. B: Peak stress in the interbody bone graft. C: Peak stress in the cage. D: Peak stress in the endplate. E: Peak stress at the bone-screw interface. F: Peak stress in the screw-rod system.

Fig.7 Stress nephogram of the endplate, interbody bone graft, cage, and screw-rod system.

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