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Morphological and Kinematic Aspects of Human Spine - As Design Inputs for Developing Spinal Implants

Abstract

Partha Sarathi Banerjee, Amit Roychoudhury and Santanu Kumar Karmakar

In present time, pain and stiffness in the cervical region of spine has become quite a common phenomena owing to the urbanized lifestyle of people which involves watching television or working on desktop computer for long hours without changing sitting postures. This pain and stiffness most often results from degeneration which takes place in the spinal discs which are located in between the vertebrae. However, the concept of establishing spinal pain as being caused by Degenerative Disc Disease is still problematic and unclear. Result of analysis on an anatomically accurate and validated intact finite element model of the spine indicated that the strain energy density and stress (internal responses) in the bony vertebra adjacent to the degenerated disc increased. During last few decades, biomedical engineers have been closely working with physicians for developing effective biomechanical techniques for relieving such pain. With conventional methods of spinal arthrodesis, the adjacent-segment ROM was significantly increased but with cervical disc arthroplasty, it has been reported to be preserved at the preoperative level. Artificial inter-vertebral disc has been in use for almost two decades in mainly European and some Asian countries. However, insertion of artificial cervical disc also has many technical issues and is not without risk. Complications, including the need for resurgery, device migration and physiological bodily response to the wear debris of the implant have been reported. An in-depth knowledge about the morphological and kinematic aspects of the spine is very much essential for designing and developing any such instrumentation. These include: - (a) shape and dimensions of bone vertebrae, (b) type and estimated values of loads to which the implants will be subjected, (c) motion patterns of vertebrae at the location where degeneration has taken place. Lastly, the choice of available materials that can be safely used for developing such implants is to be finalized. After these design inputs are obtained, computational stress analysis for bone and implants and also tribological characterization is to be done for investigating the wear rate of different combinations of materials in contact – that are planned for use as implants.