Determination and analysis of normal and adverse kinetics in the cervical spine
A detailed cervical vertebra biomechanical rigid-body analysis is necessary in order to ascertain the loads and angular motion of the functional spinal unit during activities of daily living, which presently is a gap in this field of research. The enquiry into this aspect is what motivated me to carry out this research project where the information obtained would be a valuable input in refining the ISO18192 wear testing protocol for cervical intervertebral prostheses.
There are several articulating spinal disc implants that are commercially available, mostly metal-on-polymer, with different biomechanical properties. These implants are used in cervical total disc replacement (CTDR) where it is indicated as an alternative surgical intervention to fusion for cervical myelopathy and radiculopathy. The CTDR also has been shown to be more advantageous in averting the unwanted side-effects such as heterotopic ossification and adjacent segment degeneration. Like its predecessors in joint replacement, these devices are not immune to biotribological wear that commonly seen in many orthopaedic implants, with abrasion and adhesion being the most common wear mechanisms occurring. Wear testing protocol intended for the spinal intervertebral disc implant published by the International Organization for Standardization (ISO) has been widely accepted by many biotribologists owing to its composite, multidirectional motions. The composite motions of the protocol assimilate the cross-shear effect into the simulation – a better reflection to physiological wear compared to the standard issued by ASTM International. Nonetheless, the ISO protocols come short in representing the functional loading and angular displacement of the cervical spine where it has a central tendency within the motion spectrum and discounting the extreme ends during the adverse movements of the neck.