Pure moment testing for spinal biomechanics applications: fixed versus 3D floating ring cable-driven test designs

Area of Science:

• Biomechanical Engineering
• Spine Biomechanics
• Medical Device Testing

Background:

• Pure moment testing is crucial for evaluating spinal device effects on bending rigidity.
• Cable-driven systems are common for pure moment testing due to simplicity.
• Traditional fixed loading rings in these systems have shown accuracy and validity concerns.

Purpose of the Study:

• To compare the accuracy of a novel 3D floating ring design against a traditional fixed ring design for pure moment testing of the spine.
• To assess loading conditions during multi-axial bending, lateral bending, and axial torsion tests.
• To evaluate the impact of ring design on applied moments and induced shear forces.

Main Methods:

• Conducted multi-axial bending tests on an artificial lumbar spine using both fixed and 3D floating ring designs.
• Utilized a cable-driven apparatus and a multi-axial load cell to monitor applied moments.
• Tested various configurations to assess performance under different loading conditions.

Main Results:

• The fixed ring design exhibited significant deviations (up to 77%) from intended moments.
• The fixed ring design induced substantial shear forces (up to 18 N) during testing.
• The 3D floating ring design demonstrated improved accuracy and uniform loading conditions.

Conclusions:

• The traditional fixed ring design introduces considerable errors in pure moment testing.
• The novel 3D floating ring design offers a more accurate and reliable method for spine biomechanics research.
• The 3D floating ring setup is recommended for future pure moment testing with cable-driven apparatus.