Ex vivo biomechanical testing of a three-dimensional printed titanium plate and spacer construct and 4.5 mm locking compression plate for ventral cervical fusion of C4-C5 in the horse.

Overview

• This study compares the biomechanical performance of a 3D printed titanium plate and spacer (3DM) versus a traditional 4.5 mm locking compression plate (LCP) for ventral cervical fusion at the C4-C5 vertebrae in horses.
• Both devices showed similar strength and stiffness in bending tests, but the 3DM construct was less prone to failure modes like screw pullout or displaced fractures in extension.

Background and Purpose

• Ventral cervical fusion is a surgical procedure used to stabilize the cervical vertebrae in horses, commonly at the C4-C5 level.
• Traditional fixation using a 4.5 mm broad locking compression plate (LCP) is commonly applied but may have limitations such as screw pullout or vertebral fractures.
• Emerging technology of 3D printing allows for custom-made titanium plates and spacers (3DM), which could potentially improve biomechanical outcomes.
• The purpose of this study was to compare the biomechanical properties—specifically yield moment, failure moment, and stiffness—of the 3DM device against the standard LCP during simulated mechanical testing.
• It aimed to assess differences in mechanical performance and modes of failure under flexion and extension loading.

Methods

• Twenty-four equine cervical spines were harvested post-mortem and randomly allocated to fixation with either the 3DM device (n=12) or the LCP (n=12) at the C4-C5 intervertebral space.
• Two types of mechanical tests were performed on each group:
  • Flexion testing (bending forward) on 6 spines per group.
  • Extension testing (bending backward) on 6 spines per group.
• Four-point bending tests were run until failure in a single cycle for each specimen.
• Measured outcomes were:
• Yield moment: the bending moment where irreversible deformation begins.
• Failure moment: the bending moment at which structural failure occurs.
• Stiffness: resistance of the construct to bending deformation.
• Statistical analyses:
  • Mixed effects linear regression compared yield, failure moments, and stiffness between the two groups.
  • Penalized logistic regression compared failure modes (e.g., screw pullout, displaced fractures).
  • Significance threshold set at p ≤ 0.05.

Results

• Yield moment, failure moment, and stiffness showed no significant differences between the 3DM and LCP groups in both flexion and extension conditions, demonstrating comparable mechanical performance.
• Failure modes differed in extension:
  • The LCP group had a significantly higher incidence of displaced vertebral fractures (p = 0.03).
  • Screw pullout tended to be more common in the LCP group, although this did not reach statistical significance (p = 0.09).
• The 3DM constructs were less likely to fail by displaced fracture when loaded in extension.

Conclusions and Implications

• The 3D printed titanium plate and spacer provided biomechanical stability equivalent to the established LCP system for ventral fusion at C4-C5 in horses.
• However, the different modes of failure suggest the 3DM constructs may offer an advantage by reducing risk of certain complications like displaced fractures and screw pullout, particularly during extension movements.
• These findings highlight the potential clinical benefits of 3D printed constructs in equine spinal surgery.
• A major limitation noted was the sample size; smaller yet potentially clinically relevant differences might not have been detected.
• The study recommends further in vivo evaluation to confirm these biomechanical advantages and assess biological responses, healing, and long-term outcomes.