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Title: A computational fluid dynamics analysis of the distraction forces experienced by stent-grafts following fenestrated Endovascular Aneurysm Repair
Author: Jones, Steven
ISNI:       0000 0004 6058 6605
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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Introduction One option for repair of abdominal aortic aneurysms with inadequate length of infrarenal neck is fenestrated Endovascular Aneurysm Repair. Significant complications may be caused by stent-graft migration and component distraction which are both resisted by fixation force and provoked by haemodynamic distraction force. The hypotheses tested in this thesis are that larger angulation of vessels is associated with greater distraction force and that greater distraction force is associated with higher incidence of migration and component distraction. Method Interobserver variation of a new method of angle measurement was compared with the standard method currently in use in our unit. Computer models of complete fenestrated stent-grafts and their individual components (proximal body, distal body and limb extensions) were then constructed based on the postoperative computed tomography scans of 54 patients. Computational Fluid Dynamic analysis in steady state was used to quantify the distraction force acting on each device. Blood pressure was kept constant at 160mmHg and the impact of morphological features upon distraction force was assessed. To test the second hypothesis, patient-specific blood pressures were used to obtain in situ distraction forces that were then related to the incidence of migration and component distraction. Results There were no significant differences between the old and new methods of angle measurement (p=.723, WSR). Inlet cross-sectional area (XSA) exhibited a strong, positive correlation with total RDF in complete stent-grafts, proximal body and distal body components. Outlet angulation ≥45° was significantly associated with greater total RDF in complete stent-grafts and limb extension components (Median total RDF in complete stent-grafts with angle < 45° = 2.6N vs 6.2N in those ≥45°, p < .001. Limb extensions: 1.4N vs 2.1N, p = .004, MWU). There was no significant difference between total RDF acting on the proximal or distal bodies that underwent migration or component distraction versus those that did not. Limb extensions that were observed to migrate were exposed to significantly greater total RDF compared to those that did not migrate (Median total RDF 2.9N, range 2.7-6.3N versus 1.6N, range 0.4-3.8N, p = .003, MWU). Conclusions For a given blood pressure XSA was the most important morphological determinant of total RDF. Outlet angulation of complete stent-grafts and limb extensions was associated with significantly greater total RDF. In limb extensions, greater distraction force was significantly associated with migration. The results suggest caution when planning distal seal in ectatic iliac vessels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: RD Surgery