Intradiscal pressurisation predicts intervertebral disc herniation: insights from a low-cost, open-source loading rig

Area of Science:

• Biomedical Engineering
• Orthopedics
• Spinal Biomechanics

Background:

• Ex vivo biomechanical research is crucial for understanding disc herniation and developing spinal treatments.
• Current commercial systems for multi-axis loading are often costly or mechanically restrictive, hindering research.
• Reproducing physiologically relevant loading conditions remains a significant challenge in spinal biomechanics.

Purpose of the Study:

• To develop a low-cost, open-source experimental rig for simulating physiologically relevant multi-axis loading conditions.
• To characterize the performance of the developed rig under various loading scenarios.
• To evaluate the rig's capability in inducing disc herniation in ex vivo models.

Main Methods:

• Development of an open-source rig integrating with standard hydraulic testing machines, adding flexion-extension capabilities.
• Rig characterization using uniaxial, cyclic, and three-degree-of-freedom loading protocols.
• Evaluation of prolonged cyclic loading and flexion-compression to failure on bovine tail discs (n=18) instrumented with pressure probes.

Main Results:

• The rig demonstrated precise load application with off-axis moments <0.5 Nm and RMS errors ≤2% for axial compression/rotation and ≤7% for lateral bending.
• Accurate load application was confirmed up to 2 Hz, with reduced accuracy at 10 Hz.
• The rig successfully induced disc herniation in bovine tail discs, with the pressure-force slope discriminating herniation status (AUC=0.92, p<0.001).

Conclusions:

• The developed open-source rig provides a cost-effective and mechanically capable solution for physiologically relevant multi-axis loading in spinal research.
• The rig reliably induces disc herniation in ex vivo models, facilitating further investigation into herniation mechanisms.
• Intradiscal pressurization was identified as a significant predictor of disc herniation, offering insights for diagnostic and therapeutic strategies.