Smoothed Particle Hydrodynamics to Model Spinal Canal Occlusion of a Finite Element Functional Spinal Unit Model under Compression

Compressive impacts on the cervical spine can result in bony fractures. Bone fragments displaced into the spinal canal produce spinal canal occlusion, increasing the potential for spinal cord injury (SCI). Human body models (HBMs) provide an opportunity to investigate SCI but currently need to be improved in their ability to model compression fractures and the resulting material flow. Previous work to improve fracture prediction included the development of an anisotropic material model for the bone (hard tissues) of the vertebrae assessed in a functional spinal unit (FSU) model. In the FSU model, bony failure was modeled with strain-based element erosion, with a limitation that material that could occlude the spinal canal during compression was removed when an element was eroded. The objective of this study was to implement a multi-physics modeling approach, using smoothed particle hydrodynamics (SPH) with element erosion, to simulate the movement of fractured material during central compression of a C5-C6-C7 cervical spine segment and assess spinal canal occlusion. The calculated maximum occlusion in the original model was 11.1%. In contrast, the enhanced model with SPH had a maximum occlusion of 79.0%, in good agreement with the average experimental maximum occlusion of 69.0% for age-matched specimens. The SPH implementation to preserve fractured material volume enabled the assessment of spinal canal occlusion.