Development of a low imaging signature cervical spine disc arthroplasty

Abstract

Spinal disc replacements have the fundamental goal of pain relief while prolonging lifespan of adjacent intervertebral discs. This study focuses on reducing magnetic resonance (MR) artefacts, thereby improving the post-operative imaging qualities of the Kineflex cervical disc arthroplasty. Magnetic resonance imaging (MRI) is used to evaluate the success of the resulting design, as it provides the greatest distinction between various cellular types, and is the technique of choice for spinal diagnosis. Initial research includes a survey of the most recent findings regarding cervical kinematics, the pathology of degenerative disc disease, treatments of cervical myelopathy and radiculopathy, and the complications associated with total disc replacement. The influence of modern imaging techniques and the properties of common biomaterials are investigated to obtain the basis for development. Reducing the occurrence of MR arte facts is achieved through material selection and design adaptation. Various biomaterials used in spinal applications are evaluated for their clinical performance. Smaller artifacts are achieved by replacement of cobalt-chromium-molybdenum (CCM) of the original device, with a combination of polyether-ether-ketone (PEEK) and titanium due to a lower magnetic susceptibility Testing of the device is performed in two phases: verification and validation. The prototype device is successfully verified by means of MR, computed tomography (CT) and fluoroscopy imaging of a human cadaver spine with the device in the C5-6 position. Successful verification of the prototype warranted further development. After reviewing manufacturing techniques, validation is achieved on a production-ready device to characterise the MR signature of the end product. Artefact area is reduced from 1842mm² to 242mm², allowing for visibility of both spinal nerve roots and adjacent inter-vertebral discs. The spinal canal remains affected by encroachment of artefacts by 2-3mm, but the improvement in imaging signature over the existing CCM device is significant. The resulting Kineflex product is expected to find considerable application in industry.