Limb flexion-induced axial compression and bending in human femoropopliteal artery segments

Abstract

Background: High failure rates of femoropopliteal artery (FPA) interventions are often attributed in part to severe mechanical deformations that occur with limb movement. Axial compression and bending of the FPA likely play significant roles in FPA disease development and reconstruction failure, but these deformations are poorly characterized. The goal of this study was to quantify axial compression and bending of human FPAs that are placed in positions commonly assumed during the normal course of daily activities.

Methods: Retrievable nitinol markers were deployed using a custom-made catheter system into 28 in situ FPAs of 14 human cadavers. Contrast-enhanced, thin-section computed tomography images were acquired with each limb in the standing (180 degrees), walking (110 degrees), sitting (90 degrees), and gardening (60 degrees) postures. Image segmentation and analysis allowed relative comparison of spatial locations of each intra-arterial marker to determine axial compression and bending using the arterial centerlines.

Results: Axial compression in the popliteal artery (PA) was greater than in the proximal superficial femoral artery (SFA) or the adductor hiatus (AH) segments in all postures (P = .02). Average compression in the SFA, AH, and PA ranged from 9% to 15%, 11% to 19%, and 13% to 25%, respectively. The FPA experienced significantly more acute bending in the AH and PA segments compared with the proximal SFA (P < .05) in all postures. In the walking, sitting, and gardening postures, average sphere radii in the SFA, AH, and PA ranged from 21 to 27 mm, 10 to 18 mm, and 8 to 19 mm, whereas bending angles ranged from 150 to 157 degrees, 136 to 147 degrees, and 137 to 148 degrees, respectively.

Conclusions: The FPA experiences significant axial compression and bending during limb flexion that occur at even modest limb angles. Moreover, different segments of the FPA appear to undergo significantly different degrees of deformation. Understanding the effects of limb flexion on axial compression and bending might assist with reconstructive device selection for patients requiring peripheral arterial disease intervention and may also help guide the development of devices with improved characteristics that can better adapt to the dynamic environment of the lower extremity vasculature.

Figure 1

CT of the limb flexion states demonstrating Standing (180°), Walking (110°), Sitting (90°), and Gardening (60°) postures. Bending angle is defined as the inner angle between the femur and tibia. Note severe deformations at the Adductor Hiatus and below the knee. Intra-arterial markers are blue. SFA = Superficial Femoral Artery, AH = Adductor Hiatus, PA = Popliteal Artery.

Figure 2

CTA reconstructions of the artery (red), luminal centerline, and intra-arterial markers (blue) used for the measurement of axial compression. Radii (r, green) of best-fit spheres inscribed along the centerline indicate higher degrees of bending with smaller radii. Bending angles α were also calculated using the same inscribed spheres and three points along the arterial centerline.

Figure 3

Average Axial Compression in the Superficial Femoral Artery (SFA), Adductor Hiatus (AH) and Popliteal Artery (PA) in the walking (110°), sitting (90°) and gardening (60°) postures. Box extends to 25^th and 75^th percentiles, median is marked with a red horizontal line and mean values are marked with a blue asterisk.

Figure 4

Minimum (dark box) and average (light box) bending angles α in the SFA, AH and PA in all postures. Note more acute α angle with increased limb flexion.