Comparison of the Load-sharing Characteristics between Pedicle-based Composite and Rigid Rod Devices

1. Introduction Adjacent segment degeneration (ASD) has been reported as the one of late serious complication after spinal fusion surgery [1-3]. Presumably, the immediate rigidity produced by instrumentation causes more stress leading to accelerated degeneration at adjacent levels [2]. Many previous studies have been corroborated a trend toward earlier development of ASD with instrumentation as well. In contrast, posterior dynamic stabilization (PDS) has been used to overcome the adjacent segment degeneration, one of the serous complications after lumbar fusion. Non-fusion technologies have been developed with the goal of reducing the incidence of arthrodesis-related morbidity. Implant types include total disc replacements, prosthetic nuclear implants and posterior dynamic stabilization devices. Although implants offer some theoretical advantages over fusion, new potential problems such as mechanical failure, device migration, same level degeneration and implant subsidence are associated with new technologies. Furthermore, the efficacy of non-fusion implants in the prevention of adjacent level degeneration was not yet proved. The popularity of non-fusion implants is based more on the lack of satisfaction with conventional spinal fusion rather than their proved superiority. In addition, implants failure (17% of 24 patients) after a 2-years follow-up was found in one study [4]. The stress concentration was suspected to be the main cause of screw breakage [5]. Screw breakage can easily occur in PDS system, surgical technique without cage. However composite material has a good fatigue-failure characteristic. Thus it is appropriate for PDS material. Therefore, in this study, comparison of the biomechanical property of woven composite rod (WCR) with rigid-rod lumbar fusion was evaluated.