In Vivo Morphological Changes of the Femoropopliteal Arteries due to Knee Flexion After Endovascular Treatment of Popliteal Aneurysm

Abstract

Purpose: To evaluate morphological changes of the femoropopliteal (FP) arteries due to limb flexion in patients undergoing endovascular treatment of popliteal artery aneurysms (PAAs). Materials and Methods: Seven male patients (mean age 68 years) underwent endovascular treatment of PAA with a Viabahn stent-graft between January 2013 and December 2017. During follow-up, one contrast-enhanced computed tomography angiography (CTA) scan of the lower limbs was acquired for each recruited patient. A standardized CTA protocol for acquisitions in both straight-leg and bent-leg positions was used to visualize changes in artery shape due to limb flexion. Three-dimensional reconstruction of the FP segment was performed to compute mean diameter and eccentricity of the vascular lumen and to measure length, tortuosity, and curvature of the vessel centerline in 3 arterial zones: (A) between the origin of the superficial femoral artery and the proximal end of the stent-graft, (B) within the stent-graft, and (C) from the distal end of the stent-graft to the origin of the anterior tibial artery. Results: After limb flexion, all zones of the FP segment foreshortened: 6% in zone A (p=0.001), 4% in zone B (p=0.001), and 8% in zone C (p=0.07), which was the shortest (mean 4.5±3.6 cm compared with 23.8±5.7 cm in zone A and 23.6±7.4 cm in zone B). Tortuosity increased in zone A (mean 0.03 to 0.05, p=0.03), in zone B (0.06 to 0.15, p=0.005), and in zone C (0.027 to 0.031, p=0.1). Mean curvature increased 15% (p=0.05) in zone A, 27% (p=0.005) in zone B, and 95% (p=0.06) in zone C. In all zones, the mean artery diameter and eccentricity were not significantly affected by limb flexion. Conclusion: Limb flexion induces vessel foreshortening and increases mean curvature and tortuosity of the FP segment both within and outside the area of the stent-graft.

Keywords: endovascular treatment; femoropopliteal segment; foreshortening; limb flexion; medical image analysis; morphology; popliteal artery aneurysm; stent-graft; superficial femoral artery; tortuosity.

Figure 1.

Computed tomography angiography acquisition in standardized (A) bent-leg and (B) straight-leg positions.

Figure 2.

Subdivision of the femoropopliteal segment into 3 zones: (A) between the origin of the superficial femoral artery (red) and the proximal end of the stent-graft (blue), (B) from the proximal to the distal end of the stent-graft (blue), and (C) from the distal end of the stent-graft to the origin of the anterior tibial artery (red).

Figure 3.

Three-dimensional reconstructions of the femoropopliteal segment (red), stent-graft (blue), and bones (gray) in 7 patients (P) recruited for this study. Two different views are presented for each patient.

Figure 4.

Diameter reduction in the stent-graft segment due to limb flexion in 2 patients. Left: Contour plots depicting changes in artery diameter along the length of the segmented femoropopliteal arteries. Right: Change in femoropopliteal diameter along the length of the stent-graft zone in straight (blue) and bent (red) positions. Nominal stent-graft diameters are depicted with black dashed lines; 2 partially overlapping endografts are shown for the second patient.

Figure 5.

On the left, 3-dimensional reconstruction of bones and the femoropopliteal segment (red) in both straight- and bent-limb configurations from a representative patient. The stent-graft is highlighted in blue. On the right, the graph demonstrates the change in eccentricity along the length of the stent-graft segment in straight and bent positions. The black dashed line denotes eccentricity of an ideal circular section. The black circle highlights the zone where eccentricity reduction was observed during limb flexion. Colored boxes refer to different stents.