In vitro measurement of load-sharing in spinal implants

Abstract

Efficient load-sharing in the spinal column relies on the proper working of the components of the Functional Spinal Unit (FSU). Due to various reasons such as trauma, ageing and diseases, these components or even the entire FSU can get degenerated or injured during a person’s lifetime. Spinal column reconstruction surgerieswere created with the aimto restore the functioning of the diseased or injured spine. Several spinal implants are available today for the surgeon to aid in this process. There are three major categories of these devices: anterior stabilization devices, posterior stabilization devices and motion preservation devices. This review highlights thein vitro researchdone on these devices,over the past five decades, to evaluate their ability to effectively share loads at the operated level of the spinal column. Some conclusions have been drawn based on this research.Dynamic anterior cervical plates are more successful at maintaining load-sharing after graft subsidence and anterior stabilization devices can be used to provide support to posterior stabilization devices during severe anterior column injuries. Motion preservation devices, specifically cervical disc prostheses and facet replacement systems,show great potential in maintaining physiologicalloads in the spinal column. Further clinical investigation of all these implants would help to identify the contributing factors for their success or failure post-surgery. It would also aid in determining the requirements of an ideal spine stabilization device which perfectly mimics the physiological load-sharing properties of the FSU and its components.