Development and 3D Finite Element Implementation of a Multiaxial Constitutive Relation for Abdominal Aortic Aneurysms

Geest, Jonathan Vande; Bohra, Ajay; Sun, Wei; Martino, Elena S. Di; Sacks, Michael S.; Vorp, David A.

doi:10.1115/imece2004-59643

Cited by 5 publications

(6 citation statements)

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“…27 More recent work in our laboratory has allowed the improvement of AAA stress estimation technique by the incorporation of experimentally determined tissue anisotropy into our models. 47,59 Kyriacou and Humphrey showed that the stress distribution in cerebral aneurysms is markedly different when incorporating an anisotropic model versus a simplified isotropic model, 60 and we have made similar preliminary observations for AAA.…”

Section: Estimation Of Aaa Wall Stresssupporting

confidence: 61%

Biomechanical Determinants of Abdominal Aortic Aneurysm Rupture

Vorp

Geest

2005

ATVB

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227

172

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Abstract-Rupture of abdominal aortic aneurysm (AAA) represents a significant clinical event, having a mortality rate of 90% and being currently ranked as the 13th leading cause of death in the US. The ability to reliably evaluate the susceptibility of a particular AAA to rupture on a case-specific basis could vastly improve the clinical management of these patients. Because AAA rupture represents a mechanical failure of the degenerated aortic wall, biomechanical considerations are important to understand this process and to improve our predictions of its occurrence. Presented here is an overview of research to date related to the biomechanics of AAA rupture. This includes a summary of results related to ex vivo and in vivo mechanical testing, noninvasive AAA wall stress estimations, and potential mechanisms of AAA wall weakening. We conclude with a demonstration of a biomechanics-based approach to predicting AAA rupture on a patient-specific basis, which may ultimately prove to be superior to the widely and currently used maximum diameter criterion. Key Words: abdominal aortic aneurysm Ⅲ biomechanics Ⅲ rupture Ⅲ strength Ⅲ stress A bdominal aortic aneurysm (AAA) is a focal enlargement of the infrarenal aorta, which occurs over a time course of several years. This condition is present in Ϸ2% of the elderly population, with Ϸ150 000 new cases diagnosed each year, and the incidence is increasing. 1,2 If left untreated, AAA will gradually expand until rupture; it is an event that carries a mortality rate of 90% and that is ranked as the 13th most common cause of death in the US. 3 Current AAA repair procedures are expensive and carry significant morbidity and mortality risks.Open repair of AAA is a major surgical procedure that requires patients to be hospitalized typically for 1 week and to recuperate at home for several more weeks. The mean postoperative mortality for elective repair is Ϸ5% and for emergency operations 47% (range 27% to 69%). 4 The major drawback of open repair is the compromised quality of life after surgery because of postoperative pain, the prolonged recovery period, and the high costs associated with both the surgery and the recovery.An alternative approach that avoids the extensive tissue dissection associated with open repair is the minimally invasive endovascular repair procedure. The potential advantages of endovascular AAA repair include reductions in mortality, morbidity, blood loss, hospital stay, intensive careOriginal

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Section: Estimation Of Aaa Wall Stresssupporting

confidence: 61%

Biomechanical Determinants of Abdominal Aortic Aneurysm Rupture

Vorp

Geest

2005

ATVB

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227

172

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“…More recently, patient-specific FE simulations were performed to compare the peak wall stress between ruptured or symptomatic and non-ruptured AAAs (Fillinger et al, 2002(Fillinger et al, , 2003. Despite utilizing an isotropic tissue constitutive model , and neglecting to include the presence of the ILT-each of which has been shown to influence AAA wall stress (Wang et al, 2002;Vande Geest et al, 2004a;Vande Geest, 2005)-this study found a significant difference between the groups, even when matched for equivalent maximum diameters. The peak stress for ruptured/symptomatic AAAs was 46.874.5 N/cm 2 versus 38.171.3 N/cm 2 for the electively repaired group ðp ¼ 0:05Þ.…”

Section: Clinical Application Of Aaa Biomechanicsmentioning

confidence: 89%

“…(2) and (3) may lead to an improved prediction of the stress distribution in the AAA (Fig. 9) (Vande Geest et al, 2004a;Vande Geest, 2005). Two non-ruptured and one ruptured AAA were reconstructed and subjected to two FE simulations each: one using our previous isotropic wall constitutive relation (i.e., Eq.…”

Section: Article In Pressmentioning

confidence: 97%

Biomechanics of abdominal aortic aneurysm

Vorp

2007

Journal of Biomechanics

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424

369

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Abdominal aortic aneurysm (AAA) is a condition whereby the terminal aorta permanently dilates to dangerous proportions, risking rupture. The biomechanics of AAA has been studied with great interest since aneurysm rupture is a mechanical failure of the degenerated aortic wall and is a significant cause of death in developed countries. In this review article, the importance of considering the biomechanics of AAA is discussed, and then the history and the state-of-the-art of this field is reviewed--including investigations into the biomechanical behavior of AAA tissues, modeling AAA wall stress and factors which influence it, and the potential clinical utility of these estimates in predicting AAA rupture.

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“…The intraluminal thrombus was included in the FEM stress simulations and was modeled as hyperelastic incompressible isotropic material. Following recent investigations within the authors' laboratory, 19,20 the AAA wall was modeled as an anisotropic material with a preferred stiffening in the circumferential direction. Each of the patient‐specific AAA stress simulations resulted in spatially varying estimations of local wall stress.…”

Section: Methodsmentioning

confidence: 99%

A Biomechanics‐Based Rupture Potential Index for Abdominal Aortic Aneurysm Risk Assessment

Geest

Martino

Bohra

et al. 2006

Annals of the New York Academy of Sciences

185

157

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Abdominal aortic aneurysms (AAAs) can typically remain stable until the strength of the aortic wall is unable to withstand the forces acting on it as a result of the luminal blood pressure, resulting in AAA rupture. The clinical treatment of AAA patients presents a dilemma for the surgeon: surgery should only be recommended when the risk of rupture of the AAA outweighs the risks associated with the interventional procedure. Since AAA rupture occurs when the stress acting on the wall exceeds its strength, the assessment of AAA rupture should include estimates of both wall stress and wall strength distributions. The present work details a method for noninvasively assessing the rupture potential of AAAs using patient-specific estimations the rupture potential index (RPI) of the AAA, calculated as the ratio of locally acting wall stress to strength. The RPI was calculated for thirteen AAAs, which were broken up into ruptured (n = 8 and nonruptured (n = 5) groups. Differences in peak wall stress, minimum strength and maximum RPI were compared across groups. There were no statistical differences in the maximum transverse diameters (6.8 +/- 0.3 cm vs. 6.1 +/- 0.5 cm, p = 0.26) or peak wall stress (46.0 +/- 4.3 vs. 49.9 +/- 4.0 N/cm(2), p = 0.62) between groups. There was a significant decrease in minimum wall strength for ruptured AAA (81.2 +/- 3.9 and 108.3 +/- 10.2 N/cm(2), p = 0.045). While the differences in RPI values (ruptured = 0.48 +/- 0.05 vs. nonruptured = 0.36 +/- 0.03, respectively; p = 0.10) did not reach statistical significance, the p-value for the peak RPI comparison was lower than that for both the maximum diameter (p = 0.26) and peak wall stress (p = 0.62) comparisons. This result suggests that the peak RPI may be better able to identify those AAAs at high risk of rupture than maximum diameter or peak wall stress alone. The clinical relevance of this method for rupture assessment has yet to be validated, however, its success could aid clinicians in decision making and AAA patient management.

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Development and 3D Finite Element Implementation of a Multiaxial Constitutive Relation for Abdominal Aortic Aneurysms

Cited by 5 publications

References 0 publications

Biomechanical Determinants of Abdominal Aortic Aneurysm Rupture

Biomechanical Determinants of Abdominal Aortic Aneurysm Rupture

Biomechanics of abdominal aortic aneurysm

A Biomechanics‐Based Rupture Potential Index for Abdominal Aortic Aneurysm Risk Assessment

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