title: Type IIIb Endoleak and Relining: A Mathematical Model of Distraction Forces.
abstract: OBJECTIVE
  To examine the changes in distraction force following relining of a conventional abdominal aortic stent-graft with a type IIIb endoleak using the Nellix endovascular sealing device compared to a unilateral stent-graft.
  
  
  METHODS
  Relining is often used to repair type IIIb endoleaks, but the consequences to graft stability are unknown. A mathematical model was constructed based on pressure and volume flow through the stent-grafts, incorporating recognized distraction force equations. Steady flow was presumed at peak systolic pressures to calculate the maximum distraction force, with gravity ignored. Distraction forces for 28- to 36-mm-diameter stent-graft bodies with 16-mm limbs were calculated and compared to forces following relining with single and double Nellix devices or the Renu unilateral device.
  
  
  RESULTS
  Distraction forces for the 28-, 32-, and 36-mm stent-grafts prior to relining were 5.99, 10.21, and 14.99 N, respectively. Similar forces were reported after relining with bilateral Nellix devices (5.86, 10.08, and 14.86 N, respectively). However, use of a unilateral Nellix increased the distraction forces to 9.92, 14.14, and 18.92 N, respectively. These were comparable to the increase observed after relining with a Renu unilateral stent-graft (9.87, 14.09, and 18.86 N, respectively). The proportional increase in distraction force for a unilateral relining ranged from 26% to 66%, with the greatest increase noted in the smaller diameter main bodies.
  
  
  CONCLUSIONS
  Relining a stent-graft with a type IIIb endoleak using bilateral Nellix devices does not increase the distraction force. However, a unilateral Nellix device or the Renu system could theoretically increase the distraction force by up to 66%, potentially risking migration and type Ia endoleak. In clinical practice, these results suggest that a relining with bilateral Nellix may have benefits over the Renu unilateral stent-graft.
authors: Liverpool Vascular and Endovascular Service, Royal Liverpool University Hospital, Liverpool, UK swaelenscharles@gmail.com.
authors: Charles
authors: C
authors: Swaelens
authors: School of Engineering, University of Liverpool, UK.
authors: Robert J
authors: RJ
authors: Poole
authors: Liverpool Vascular and Endovascular Service, Royal Liverpool University Hospital, Liverpool, UK.
authors: Francesco
authors: F
authors: Torella
authors: Liverpool Vascular and Endovascular Service, Royal Liverpool University Hospital, Liverpool, UK.
authors: Richard G
authors: RG
authors: McWilliams
authors: Department of Radiography, University of Salford, UK.
authors: Andrew
authors: A
authors: England
authors: Liverpool Vascular and Endovascular Service, Royal Liverpool University Hospital, Liverpool, UK.
authors: Robert K
authors: RK
authors: Fisher
mesh_terms: D001012:Aorta, Abdominal / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D017544:Aortic Aneurysm, Abdominal / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D001027:Aortography / Q000379:methods; D001807:Blood Vessel Prosthesis; D019917:Blood Vessel Prosthesis Implantation / Q000009:adverse effects / Q000295:instrumentation*; D000072226:Computed Tomography Angiography; D057867:Endoleak / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology / Q000601:surgery*; D057510:Endovascular Procedures / Q000009:adverse effects / Q000295:instrumentation*; D005548:Foreign-Body Migration / Q000209:etiology / Q000503:physiopathology; D006439:Hemodynamics; D006801:Humans; D008955:Models, Cardiovascular; D011474:Prosthesis Design; D012039:Regional Blood Flow; D012086:Reoperation; D015607:Stents; D013314:Stress, Mechanical; D016896:Treatment Outcome
keywords: abdominal aortic aneurysm; computational models; device failure; endograft; endoleak; endovascular aneurysm sealing; stent-graft