Failure properties of abdominal aortic aneurysm tissue are orientation dependent.

Abstract

Biomechanical rupture risk assessment of abdominal aortic aneurysm (AAA) requires information about failure properties of aneurysmal tissue. There are large differences between reported values. Among others, studies vary in using either axially or circumferentially oriented samples. This study investigates the effect of sample orientation on failure properties. Aneurysmal tissues from 45 patients (11 females) were harvested during open AAA repair, cut into uniaxial samples (90) and tested mechanically within 3 h. If possible, the samples were cut in both axial (49 samples) and circumferential (41 samples) directions. Wall thickness, First Piola-Kirchhoff strength P_ult and ultimate tension T_ult were recorded. Influence of sample orientation and other clinical parameters were investigated using non parametric tests. Medians of P_ult (values 1100 kPa for circumferential vs. 715 kPa for axial direction, p < 10^-4) and T_ult (17.4 N/cm in circumferential vs. 11.2 N/cm in axial direction, p < 10^-4) were significantly higher in circumferential direction. For paired data, the median of difference was 411 kPa (p < 10^-3) in P_ult and 7.4 N/cm (p < 10^-4) in T_ult in favor of circumferential direction. In this first study of anisotropy in AAA wall failure properties using paired comparisons, the strength in circumferential orientation was found to be higher than in axial orientation.