Role of neck angulation and endograft oversizing in folding and its impact on device fixation strength

Objective: To assess neck angulation and endograft oversizing as factors contributing to folding. Endograft folding will then be assessed on its role in endograft fixation strength. Methods: Bench top flow loop experiments were performed with barbless Gore Excluder endovascular grafts (EVG) that were deployed into silicone aorta-AAA models with neck angles of 0, 30, and 60. A total of five oversizings were tested: -7%, 2%, 12%, 24%, and 38% with N= 3 for each oversizing at each neck angle for a total of 45 experiments. Photographs of the stent apex to apex distances were taken for the entire circumference of the device for a total of 8 photos per experiment. Measurements of the apex to apex distance were taken for the top three stent layers and variance for each stent layer was calculated. Variances for all three stent layers were summed to represent the folding metric. The silicone model was then removed from the flow loop and placed on the uniaxial extension tester to for pull out testing to assess impact on attachment strength. Results: Neck angle and oversizing increases folding risk at oversizing ≥12% for 00 and 300 neck angles, and ≥ 2% oversizing for a 600 neck angle. Folding metric comparison between 00 vs. 300 and 00 vs. 600 across all oversizings had statistical significance (Mann-Whitney U, p<0.05). Folding decreases fixation strength at lower neck angles for oversizing ≥24%. As oversizing is increased, pull out forces increase as well. At higher neck angles, oversizing and folding has little effect on migration risk. There was no statistical difference in pull out forces across all neck angles. Conclusion: Oversizing and neck angulation contributors to folding. Folding increases migration risk for at oversizing ≥24% and lower neck angles. At higher neck angles, folding and oversizing has no impact on attachment strength.