Quantifying the Impact of Spinal Fusion Systems by Multibody Simulation

The established surgical procedure of spinal fusion, in which two or more spinal vertebrae are permanently connected, is constantly increasing worldwide due to new developments in fusion procedures and surgical techniques, as well as improved implants, even though there is still no consensus on whether fusion leads to subsequent degeneration of adjacent spinal segments. We outline the potential biomechanical impacts of mono-segmental and multi-segmental fusion on the spinal structures, especially on the adjacent functional spinal units (FSU), using MultiBody Simulation (MBS). In addition, we investigated the influence of the implant size on the loading situation of the spinal structures by analyzing suitable human MBS models, focusing on a highly detailed spinal region. Our results showed no significant increase in the load on adjacent intervertebral discs (IVD) in the present specific model configurations due to mono-segmental and multi-segmental fusion. Instead, the load was redistributed to the disadvantage of the posterior facet joints in the lumbar spine's upper section. Analysis of the influence of different implant sizes on the spinal structures' load revealed that choosing an implant size that did not correspond to the original IVD space led to a massive increase in the IVD loads.Clinical relevance: gaining new insights to improve surgical outcomes to minimize the risk of adverse effects.