The device investigation report was received and the following information was provided: the scanning electron microscope (sem) results showed the separated strut area of the stent unit presented consistent evidence of fatigue fracture on the struts' separated surface areas.Also, non-metallic inclusions were observed near to the fracture origins.It is assumed that the observed non-metallic inclusions led to fatigue crack initiation, resulting ultimately in the separation of the struts' material.The inclusions of the observed size are expected to be found in the material and are not uncommon.Fatigue fractures in this material are commonly observed to originate at inclusions such as these.Based on literature review on carotid stent fracture, it is stated that the incidence rate of fractures in self expanding carotid stents is commonly reported to be 6% or less, and fractures have generally not been associated with adverse clinical sequelae.Researchers have observed that the causes of carotid stent fracture are multivariate, involving design aspects of the specific stents, biomechanical factors related to blood flow, swallowing, and mobility of the neck, and the patient specific nature of the disease state itself, particularly calcification in the region stent implantation.Fatigue performance of nitinol components is understood to be influenced by impurities in the material, as well as localized concentration of stress and strain in the material related to unique design attributes of each component, as well as biomechanical forces and deformations that are unique to each anatomical region of the body, and to some extent to each individual patient.Please see the em-020414-a-20210115a literature review, sem technical results, and product evaluation report attached under file attachments.
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