Limb flexion-induced twist and associated intramural stresses in the human femoropopliteal artery

Abstract

High failure rates of femoropopliteal artery (FPA) interventions are often attributed to severe mechanical deformations that occur with limb movement. Torsion of the FPA likely plays a significant role, but is poorly characterized and the associated intramural stresses are currently unknown. FPA torsion in the walking, sitting and gardening postures was characterized in n = 28 in situ FPAs using intra-arterial markers. Principal mechanical stresses and strains were quantified in the superficial femoral artery (SFA), adductor hiatus segment (AH) and the popliteal artery (PA) using analytical modelling. The FPA experienced significant torsion during limb flexion that was most severe in the gardening posture. The associated mechanical stresses were non-uniformly distributed along the length of the artery, increasing distally and achieving maximum values in the PA. Maximum twist in the SFA ranged 10-13° cm^-1, at the AH 8-16° cm^-1, and in the PA 14-26° cm^-1 in the walking, sitting and gardening postures. Maximum principal stresses were 30-35 kPa in the SFA, 27-37 kPa at the AH and 39-43 kPa in the PA. Understanding torsional deformations and intramural stresses in the FPA can assist with device selection for peripheral arterial disease interventions and may help guide the development of devices with improved characteristics.

Keywords: femoropopliteal artery; intra-arterial markers; mechanical stress; peripheral artery disease; torsion.

Figure 1.

(a) Three-dimensional reconstruction of a silicone tube in the free (unpinned, left) and deformed (pinned, right) configurations twisted to 0°, 45°, 90° and 180° using hypodermic needles. (b) Intra-arterial markers on a string separated by glass beads and assessment of torsion in a silicone tube bent and twisted to 45°, −45°, 90°, −90°, 180° and −180°. (c) Schematic of angle measurement using two consecutive markers. (Online version in colour.)

Figure 2.

(a) Schematic of the three arterial segments and main anatomic markers used in this study. (b–e) CTA of the limb flexion states demonstrating (b) standing (180°), (c) walking (110°), (d) sitting (90°) and (e) gardening (60°) postures. Note severe deformations of the femoropopliteal artery at the AH and below the knee. Intra-arterial markers are blue.

Figure 3.

Measurement of limb flexion-induced FPA torsion in a segment of the PA. Left panel represents the straight limb posture, while right panel represents the bent limb posture. Two-dimensional cross-sectional CT images of the markers are obtained along the arterial centreline. Note the change in orientations of the markers relative to each other in both postures.

Figure 4.

(a) A representative distribution of torsion along the normalized lengths of the SFA and PA in the walking (110°), sitting (90°) and gardening (60°) postures. (b) Distribution of Green shear strains along the normalized lengths of the SFA and PA in the gardening (60°) posture. SFA spans from the take off of the profunda femoris artery (PF) to the adductor hiatus (AH) segment. PA starts at the AH and continues to the tibial peroneal trunk (TPT). Note gradually higher torsion with increasing limb flexion and its non-uniform distribution along the length of the FPA. (Online version in colour.)

Figure 5.

Maximum twist in the superficial femoral artery (SFA), adductor hiatus segment (AH) and popliteal artery (PA) in the walking (110°), sitting (90°) and gardening (60°) postures. Box extends to 25th and 75th percentiles, median is marked with a red horizontal line and mean values are marked with a blue dot. (Online version in colour.)

Figure 6.

(a) A representative graph of the biaxial experimental data and its constitutive model fit. (b) Results of the non-parametric bootstrapping demonstrating unimodal distribution of parameters. (Online version in colour.)

Figure 7.

Maximum principal stresses averaged through the thickness of the superficial femoral artery (SFA), adductor hiatus segment (AH) and popliteal artery (PA) during walking, sitting and gardening postures. Box extends to 25% and 75% confidence levels, whiskers depict data range excluding outliers, black dots correspond to mean values and horizontal bar represents median values. Outliers are marked with a plus symbol. (Online version in colour.)

Figure 8.

Shear stress due to twist σ_θz averaged through thickness in the superficial femoral artery (SFA), adductor hiatus segment (AH) and popliteal artery (PA) during walking, sitting and gardening postures. Bar graphs represent mean values of stress and error bars extend to 1 s.d. (Online version in colour.)