Biomechanical evaluation of intervertebral disc treatments

Lower back pain, which has been associated with intervertebral disc degeneration, is a leading cause of disability worldwide and is associated with a large socioeconomic cost. A proposed treatment for disc degeneration is nucleus augmentation, where a biomaterial is injected into the nucleus pulpous of the disc aiming to restore disc height and biomechanics. Current laboratory test methods have not been adapted for evaluating soft tissue mechanics. The aim of this project was to develop and utilise a suite of methods to evaluate the mechanical properties and effects of injectable treatments on the intervertebral disc. A further goal was to develop a prototype delivery device to meet the unique requirements of the University of Leeds peptide hydrogel. High magnitude loading was applied to bovine tail intervertebral discs in native, degenerated, and treated states. Discs were cyclically tested under high magnitude to 20,000 cycles aiming to exacerbate potential mechanical consequences across the different states. A rapid enzymatic degeneration procedure was performed to replicate an early stage degeneration state. Predictive modelling was applied to the 20,000 cycle data and showed the mechanical behaviour in the native and degenerate states can be estimated with approximately 1,000 to 5,000 cycles. A further study was performed using 1,000 cycles which evaluated different parameters with respect to mechanical restoration. The test method found a strong relationship with the clinically measurable parameters volume injected (r2=0.7) and change in disc height from the injection (r2=0.8). The developed bovine tissue in vitro model was transferred to human tissue. Several issues with the transfer were addressed and a preliminary set of data was analysed. Finally, a novel prototype device was developed that is able to deliver the University of Leeds patented hydrogel. In vitro and clinical studies were completed to evaluate the efficacy of the novel device. These studies examined the performance of the design and highlighted the need to assess the delivery requirements for injectable treatments. Overall, a suite of tests has been developed that were able to mechanically evaluate the performance of injectable nucleus augmentation treatments. Mechanical testing was shown to be an important factor that can help optimise the surgical process, mitigate risks, and contribute towards clinical translation.