In vivo characterisation of 3D intervertebral disc strains

Low back pain is the leading cause of disability worldwide and is estimated to cost the NHS £500 million annually. A link has been found between degeneration of the intervertebral discs and low back pain, suggesting degeneration may be a contributing factor. Identifying patients where this is the case is not straight forward, particularly as it is possible to have degenerate discs without experiencing any pain at all.

Initially, patients with low back pain are treated conservatively, but for those who require surgery, fusion of the vertebrae is the most common procedure, although increasingly total or partial disc replacement technologies are considered to preserve motion at the joint. Outcomes from these procedures are relatively poor, with revision surgeries required in as many as 20% of patients who undergo a lumbar fusion within 10 years. Improving patient selection is important for good clinical outcomes using these treatments, however the tools currently available (usually Magnetic Resonance Imaging (MRI) or X-ray) provide little information of how the disc is functioning before a clinical decision is made. The ability to assess quantitatively the deformations within discs would provide a unique tool to allow treatments to be targeted towards appropriate patients and therefore improve outcomes.

Recent advances have been made in measuring disc deformations in human cadaveric specimens by combining a technique called Digital Volume Correlation (DVC) and MR images captured with a high-resolution research scanner (9.4T). The technique works by obtaining two sets of images of the same specimen, one unloaded, and one loaded. Three dimensional patterns within the images are then tracked between the two sets of images such that deformations and strains can be calculated. Results from this study show huge potential but a real breakthrough will come when the tool can be used clinically, this is not currently possible because the bore of research MRI scanners is less than 10cm in diameter.

This study will utilise DVC in clinical MRI scanners (that is, scanners used in every hospital to image patients) to create a non-invasive clinical method of measuring intervertebral disc deformations. This novel diagnostic tool will allow better stratification in treatment. It will also provide fresh insight into the intricate mechanics of healthy and degenerate discs, information that will guide future surgical treatments and medical device designs.