Deformed Popliteal Artery Due to Highly Flexed Knee Position Can Cause Kinks, Creating an Unfavorable Hemodynamic State

Abstract

Background: Endovascular treatment devices of the femoropopliteal artery have evolved, improving clinical results. However, the effects of dynamic changes in the popliteal artery during knee flexion have not been sufficiently investigated. In this study we performed a 3-dimensional analysis to clarify the dynamic changes in the popliteal artery during knee flexion and their effects on hemodynamics.

Methods and Results: To analyze dynamic changes in the popliteal artery in the knee flexion position, a computed tomography protocol was developed in the right-angled and maximum flexion knee positions. Thirty patients with lower extremity artery disease were recruited. V-Modeler software was used for anatomical and hemodynamic analyses. Various types of deformations of the popliteal artery were revealed, including hinge points and accessory flexions. Kinks can occur in the maximum flexion position; however, they rarely occur in the right-angled flexion position. In addition, hemodynamic analysis revealed a tendency for lower minimum wall shear stress and a higher maximum oscillatory shear index at the maximum curvature of the popliteal artery.

Conclusions: Kinks in the maximum flexion position suggested that the outcome of endovascular treatment may change in areas such as Japan, where knee flexion is customary. Hemodynamics at the maximum curvature of the popliteal artery indicated that the luminal condition was unfavorable for endovascular treatment.

The indications for endovascular treatment (EVT) of the femoropopliteal artery have expanded during the past decade with advances in relevant devices and interventional procedures. Furthermore, the length of the femoropopliteal artery recommended for EVT increased from 5 cm, recommended by the Trans-Atlantic Inter-Society Consensus-II (TASC II) in 2007, to 25 cm in recent European and Japanese guidelines.^1–3 Accordingly, EVT of lesions has increasingly expanded to the popliteal artery. Although popliteal artery lesions may be deformed by knee flexion, there is little in current guidelines regarding the effects of dynamic changes in the popliteal artery during knee flexion on hemodynamics.

Previous studies reported dynamic changes in the knee joint and popliteal artery from anatomical, orthopedic, and vascular perspectives.^4–6 Until the early 2000s, there were several reports of stent fractures in the femoropopliteal artery,^7,8 and endovascular physicians occasionally performed dynamic angiography to avoid the effects of dynamic changes in the popliteal artery due to knee flexion.^9–11 Based on dynamic angiographic findings, Diaz et al defined multiple flexion points in the popliteal artery, including the hinge point (HP) and accessory flexions (AF).¹² However, most reports using angiography are based on 2-dimensional imaging analysis. To analyze morphological changes in the popliteal artery during knee flexion, we developed a protocol of capturing 3-dimensional (3D) contrast-enhanced computed tomography (CE-CT) in the right-angled and maximum flexion positions. In addition, we developed an image-based modeling system (V-Modeler) to extract vascular geometry and identify geometric parameters, such as curvature and torsion, and perform hemodynamic simulations.^13,14

Using these modalities and techniques, we aimed to analyze the morphological and hemodynamic changes, including wall shear stress (WSS) and oscillatory shear index (OSI), of the popliteal artery with knee flexion. This 3D analysis outlines the structural changes of kinks, along with hemodynamic changes of WSS and OSI. This can highlight dynamic changes in the popliteal artery and, accordingly, provide better endovascular treatment.

Methods

Participants

Thirty patients with lower extremity arterial disease (LEAD), aged >20 years, and with an ankle–brachial index <0.9 were recruited to this study. All the patients were recruited from outpatients visiting the Division of Vascular Surgery at the University of Tokyo Hospital. The exclusion criteria were a history of LEAD treatment for femoropopliteal lesions or artificial joints in the lower limb, decreased renal function (estimated glomerular filtration rate <45 mL/min/1.73 m²; patients undergoing dialysis were included), contrast agent allergy or asthma, or an inability to bend the knee. Patients underwent CE-CT in the normal (extended limb) position. After a period of over 1 month and within 1 year, patients underwent CE-CT in 2 leg positions: (1) right-angled flexion (approximately 90°), which mimicked the sitting position; and (2) maximum flexion (approximately 135°), which mimicked the crossed leg or gardening position (Figure 1).

Figure 1.

Leg flexion position of (A) right-angled flexion (90°) and (B) maximum flexion (135°). Images show the positions used during the contrast-enhanced computed tomography imaging, along with the sitting and crossed leg positions that mimic them.

CE-CT was performed using a 320-multidetector row CT scanner (Aquilion PRISM Edition; Canon Medical Systems, Otawara, Japan). The scanning parameters were as follows: thickness, 5.0 mm; interval, 5.0 mm; pitch factor, 0.813; rotation time, 0.5 s; field of view, 50 cm; and matrix, 512×512 pixels. For each patient, an 22-G intravenous catheter was placed in the median cubital vein of the upper limb and contrast medium was injected using an injector. When performing CE-CT in the normal position, contrast (2 mL/kg iohexol; Omnipaque 350; GE HealthCare, Tokyo, Japan) was administered at a flow rate of 2.5 mL/s. The trigger to start scanning was obtained for each patient individually using the bolus tracking technique, with a trigger level of 180 Hounsfield units to obtain optimal intraluminal contrast enhancement. The trigger was placed 5 cm above the proximal edge of the patella. When CE-CT imaging was performed in the knee flexed positions, contrast (1 mL/kg iohexol) was administered at a flow rate of 2.3 mL/s in the right-angled and maximum bending positions. Five minutes after imaging in the right-angled position, the same scan was performed in the maximum bending position. All images were obtained at the aortic bifurcation of the toes.

Analysis images, with a thickness of 1.0 mm and an interval of 0.8 mm, were created from the raw data using reconstruction software (Advanced Intelligent Clear-IQ Engine; Canon Medical Systems). Segmentation of the femoropopliteal artery was performed using Ziostation2 (Ziosoft, Tokyo, Japan; Figure 2). The primary analysis was performed using another software package (V-Modeler; see below). Chronic total occlusion and severe stenosis were detected by CE-CT in the iliac, common femoral, superficial femoral, popliteal, and tibial arteries (Table 1).

Figure 2.

Computed tomography images of the front and side views of the femoropopliteal artery at the normal, 90°, and 135° flexion positions (Patient 1).

Table 1.

Patient Demographics and Risk Factors (n=30)

Right/left (n)	13/17
Males/females (n)	20/10
Age (years)	73.4±6.0
Dialysis	10% (3)
Hypertension	73% (22)
Dyslipidemia	80% (24)
Diabetes	60% (18)
History of smoking	73% (22)
ABI	0.66±0.15
Rutherford’s classification
0	11
1–3	19
4–6	0
Reference vessel diameter (mm)
P1 segment	5.23±0.96
P3 segment	4.62±0.90
Chronic total occlusion or severe stenosis
Iliac artery	20% (6)
Common femoral artery	33.3% (10)
Superficial femoral artery	50% (15)
Popliteal artery	20% (6)
Tibial artery	50% (15)

Unless indicated otherwise, data are given as the mean±SD. ABI, ankle-brachial index.

The study protocol was approved by the Institutional Research Ethics Committee of The University of Tokyo Hospital (Approval no. 2021196NI). Written informed consent was obtained from all participants.

Vascular Image Reconstruction Using V-Modeler

We segmented the arterial lumen from each slice of CT images and extracted the centerlines using V-Modeler, as described in our previous studies.^13,14 During the process of segmentation using V-Modeler, stenosis and occlusive lesions due to arteriosclerosis were complemented semimanually to eliminate them from the analysis, allowing for the pure evaluation of deformation due to mechanical forces accompanying changes in lower limb position. The curvature and torsion of the centerline can also be obtained using the geometric parameters gotten using V-Modeler.^13,14 In addition to V-Modeler, Integrated Computer Engineering and Manufacturing (ICEM) code for computational fluid dynamics (CFD) version 18.0 (Research Center of Computational Mechanics, Tokyo, Japan) was used for meshing, OpenFOAM extended version (The OpenFOAM Foundation, London, UK) was used for simulation, and ParaView version 5.9.0 (Kitware, Clifton Park, NY, USA) was used for post-processing of simulation data. MATLAB version R2022b (MathWorks, Natick, MA, USA) was used for WSS and OSI calculations of patient-specific femoropopliteal arteries.

Mesh Construction, Physical Properties, and Boundary Conditions

To confirm the trend in hemodynamic changes associated with dynamic changes in the femoropopliteal artery, we performed a CFD analysis on 3 patients who initially underwent imaging. These patients had few arteriosclerotic changes in the popliteal artery region; furthermore, their HP formations and characteristic AF were typical. We aimed to perform CFD simulation on normal controls with no obvious calcifications to appropriately examine the procedure; accordingly, we choose these patients. Later, and based on the segmentation step, we created mesh models with the ICEM software using V-Modeler to perform numerical simulations. Before the simulation began, mesh criterion verification was performed on the mesh models created. The mesh resolution can be determined by the non-dimensional distance from the wall, denoted by the parameter y⁺. This parameter is defined as follows:

  

$y^{+}=\frac{y\times u_{\tau }}{v},u_{\tau }=\sqrt{\frac{{\tau }_w}{\rho }}$

where y is the first prism layer thickness, u_τ is the friction velocity, v is the kinematic viscosity of the blood flow, τ_w is the WSS, and ρ is the density of the blood flow.

  

$y_{firstprismlayer}=y^{+}\sqrt{\frac{vR}{2u_{\max }}}$

where v is the kinematic viscosity of the fluid, R is the radius of the artery, and u_max is the maximum velocity of blood flow at the inlet of the model. The variable y⁺ serves as an indicator to establish the first grid point from the wall, enabling the resolution of significant velocity gradient changes near the wall. Therefore, the mesh resolution criteria were set as follows:

• $y^{+}<1$

• increasing ratio of the grids between 1.1 and 1.25

• total height of the prism layer between 10% and 15% of the artery diameter.

All 3 representative cases were meshed satisfying the above criteria mentioned.

Reference vessel diameters were defined as the most normal-looking cross-sections within the same arterial segment.¹⁵

The physical properties and boundary conditions were defined as follows: density of blood 1,060 kg/m³; and viscosity of blood 0.0047Pa∙s.

The inlet velocity was set as the pulsatile flow boundary condition as follows:^16,17

  

$u=2U_{ave}\left(1-{\left(\frac{r}{r_0}\right)}^2\right)\times \left(1+\sin \left(2\pi t\right)\right)$

  

$U_{ave}=0.03m/s;Re=88$

where U_ave is the average velocity of the inlet of the model, r is the distance between the point and center of the inlet, and r₀ is the radius of the inlet, which is equal to 6 mm. The Reynolds number (Re) is a dimensionless quantity that characterizes the flow regime, indicating whether a flow is laminar or turbulent. It is defined as Re=UD/v, where U is a characteristic velocity, D is a characteristic length scale, and v is the kinematic viscosity of the fluid. In this study, the corresponding Re value for the cases was 88, classifying the flow as laminar. No-slip wall and zero-pressure gradient outlet boundary conditions were used in the numerical simulation.

Time-Averaged Wall Shear Stress and Oscillatory Shear Index

Time-averaged wall shear stress (TAWSS) was calculated by integrating each nodal WSS magnitude over the pulse cycle. OSI is a dimensionless metric that characterizes whether a WSS vector is aligned with a TAWSS.¹⁶ To obtain the distribution of TAWSS and OSI along the targeted model, the WSS information at each point of the wall boundary of the model over time could be obtained from the simulation results. Thereafter, the WSS value of each point at different time was output into an Excel file using MATLAB software to summarize the distribution of TAWSS and OSI based on the following equations:

  

$TAWSS=\frac{1}{T}{\displaystyle {\int }_0^T\left|{\tau }_w\right|}dt$

  

$OSI=0.5\times \left(1-\frac{\left|{\displaystyle {\int }_0^T{\tau }_{w}dt}\right|}{{\displaystyle {\int }_0^T\left|{\tau }_w\right|dt}}\right)$

where τ_w is the instantaneous WSS vector, t is time, and T is the pulse cycle period. Finally, the TAWSS and OSI of the targeted model were output, and the results were visualized using ParaView Software.

HP and AF

The HP was defined as the first curve in the PA at an acute angle toward the femur that appeared during knee flexion. AF was defined as any curve in the popliteal artery (other than the HP) identified during knee flexion.^12,18 The proximal location of the HP, which was primarily surrounded by the vastus medialis and semimembranosus muscles, was defined as the pre-HP segment. The distal location of the HP, which was primarily surrounded by the gastrocnemius muscle, was defined as the post-HP segment. The pre- and post-HP segments were analyzed separately because the structural mechanisms that induced AF were assumed to differ for these 2 locations.

The position of the HP during knee flexion is commonly close to that of the proximal edge of the patella in the knee-extended position. In the classification of the popliteal artery in the knee-extended position, the segments are defined as follows (Figure 3): P1: from the adductor hiatus to the proximal edge of the patella, P2: from the proximal edge of the patella to the center of knee joint space, and P3: from the center of knee joint space to the origin of anterior tibial artery. Moreover, the boundary between the P1 and P2 segments is the proximal edge of the patella; accordingly, the patella is a useful marker for estimating the position of the HP in the extended position. Therefore, the P1 and combined P2 and P3 segments can be used to reference the pre- and post-HP segments, respectively^12,18 (Figure 3).

Figure 3.

Dynamic changes in the popliteal artery and kink frequency at the 90° and 135° flexion positions. AF, accessory flexion; HP, hinge point.

Kink

Clinically, we have used the word “kink” as the narrowing of the lumen caused by the bending of the artery under compression. In this study, we defined “kink” as a narrowing of the lumen area in the extended position by ≥70% under knee flexion, referencing the ultrasound diagnosis where stenosis ≥70% is typically considered “severe” when accompanied by elevated flow velocity^19–21 (Figure 4). Furthermore, we investigated whether the presence of a kink in the flexed position lowers the ankle-rachial index (ABI) using Student’ t-test.

Figure 4.

Definition of kink: narrowing of the lumen area ≥70% in the knee flexion position.

Statistical Analysis

Data were analyzed using Microsoft Excel version 16.76 (Microsoft, Albuquerque, NM, USA). Continuous values are expressed as the mean±SD. P<0.05 (two-tailed) was considered significant. Student’s t-test was used to compare ABI between cases with and without a kink. Statistical analyses were performed using JMP version 17.2 (JMP Japan, Tokyo, Japan).

Results

Patients

We performed CE-CT on 30 patients with LEAD between November 2021 and April 2023. The knee joint angles at right-angled flexion were 90.9±7.3° and those at maximum flexion were 135.7±7.5°. Patient backgrounds are presented in Table 1. Patients with chronic limb-threatening ischemia were excluded. Arteriosclerotic lesions were not included in the selection criteria and ranged widely from the iliac to the tibial artery.

AF

CE-CT revealed substantial deformation of the popliteal artery during knee flexion. Bends are often overlooked by routine angiography alone when performing 3D observations (Figure 3).

HP

HPs were observed in all 30 patients (100%). Kinks occurred in 11 (36.7%) patients at the HP during maximum flexion; however, only 1 kink occurred during right-angled flexion. The location of the HPs coincided with the proximal edge of the patella in the extended position in 28 (93.3%) patients. This means that kinks are likely to occur (36.7%) during maximum flexion in the region of the popliteal artery, which is close to the proximal edge of the patella in the extended position, marking the boundary between the P1 and P2 segments.

AF in the Pre-HP Segment

The pre-HP segment forms a characteristically lateral/anterior convex AF several centimeters from the adductor hiatus. It represents the first bend formed by the popliteal artery after it is released from fixation by the adductor canal (Hunter’s canal), and we included it in the P1 segment^10,12 (Figure 3). We observed this characteristic AF in 23 (76.7%) patients; additionally, 11 (36.7%) patients exhibited kinks during maximum flexion. There was only 1 patient with a kink during right-angled flexion.

AF in the Post-HP Segment

All 30 patients (100%) had AF in the post-HP segment (P2 and P3 segments). Moreover, 17 patients (56.7%) showed kinks during maximum flexion, and there were 2 cases of kinks during right-angled flexion.

Kinks

One or more kinks were observed in 4 (13.3%) and 23 (76.7%) patients during right-angled flexion of the entire popliteal artery and maximum flexion, respectively (Figure 3). No relationship was found between the ABI and the presence or absence of a kink (P=0.9849).

Hemodynamic Parameters

In this study we performed CFD analysis on 3 patients who initially underwent imaging (Patients 1–3). Blood vessel models were created using V-Modeler, the centerline was obtained using V-Modeler, and the curvatures in each of the 3 cases were calculated. After creating the mesh of the models using ICEM software, the WSS and OSI were calculated by performing numerical simulations using the OpenFOAM software with the pulsatile inlet boundary condition. For example, the distributions of the curvature, WSS, and OSI at the maximum flexion position in Patient 1 are shown in Figure 5. We analyzed changes in the WSS and OSI at the AF in the pre-HP and HP areas for all 3 representative cases (Table 2). The results showed that as the curvature of the specific point (AF or HP) increased, the minimum TAWSS decreased, and the maximum OSI increased as the patient-specific bending degree increased in all 3 cases.

Figure 5.

Computational fluid dynamics (CFD) simulations of the maximum bending position and distributions of time-averaged wall shear stress (TAWSS) and the oscillatory shear index (OSI) in Patient 1. AF, accessory flexion; HP, hinge point.

Table 2.

Hemodynamic Parameters for Each Position

Patient no.	Section	Parameter	Normal (extended)	Right-angled flexion	Maximum bending
Patient 1	AF (pre-HP segment)	Curvature	0.016	0.055	0.174
		Minimum TAWSS	0.09	0.06	0.04
		Maximum OSI	0.07	0.12	0.36
	HP	Curvature	0.015	0.095	0.217
		Minimum TAWSS	0.11	0.04	0.03
		Maximum OSI	0.09	0.32	0.45
Patient 2	AF (pre-HP segment)	Curvature	0.010	0.0364	0.1044
		Minimum TAWSS	0.35	0.08	0.06
		Maximum OSI	0.04	0.14	0.4
	HP	Curvature	0.009	0.059	0.083
		Minimum TAWSS	0.21	0.05	0.03
		Maximum OSI	0.03	0.21	0.45
Patient 3	AF (pre-HP segment)	Curvature	0.010	0.031	0.055
		Minimum TAWSS	0.18	0.15	0.1
		Maximum OSI	0.05	0.06	0.18
	HP	Curvature	0.015	0.092	0.151
		Minimum TAWSS	0.15	0.09	0.02
		Maximum OSI	0.12	0.3	0.44

AF, accessory flexion; HP, hinge point; OSI, oscillatory shear index; TAWSS, time-averaged wall shear stress.

Discussion

Dynamic popliteal artery changes due to knee flexion are important factors affecting endovascular treatment; however, their verification using 3D analysis has not been performed. Morphological changes in the popliteal artery, including the HP and AF, due to knee flexion were evaluated in 3D in this study. The “kink” occurred in the maximum flexion position; however, it rarely occurred in the right-angle flexion position. Hemodynamic analysis revealed a tendency toward a lower minimum WSS and higher maximum OSI at the maximum curvature points.

There was no relationship between the ABI and the presence or absence of kinks. This lack of association could be attributed to the fact that the ABI is primarily influenced by lesions in the iliac and femoral arteries. Moreover, all ABI measurements were performed in the extended-knee position. This could explain why kinks had no impact on ABI.

A primary concern is whether long-term outcomes of EVT for deformed popliteal lesions owing to high knee flexion are acceptable. Stent placement in the popliteal artery is avoided, anticipating a high risk of stent failure due to knee flexion. However, there is no clear evidence regarding this, and the guidelines have not explicitly warned against stent placement in popliteal lesions, as a non-stenotic zone.^1–3

In the early 2000s, Scheinert et al reported a stent fracture rate of 37.2% (45/121 treated limbs at a mean follow-up time of 10.7 months) in femoropopliteal lesions.²² A high fracture rate of 77.8% (14/18 treated limbs at the 2-year follow-up) was also reported in patients in which self-expandable nitinol stents were placed in below-the-knee popliteal lesions.²³ Improvements in stent design and material were assumed to be required in this era. In the 2010s, 3 types of innovative EVT devices became available: drug-eluting devices, heparin-bonded stent grafts (Viabahn; W.L. Gore & Associates, Flagstaff, AZ, USA), and self-expanding nitinol stents with unique laminated rigid wire structures (SUPERA: IDev Technologies, JS Beuningen, Netherlands). These have improved the results of EVT for femoropopliteal artery lesions. However, few studies have focused exclusively on popliteal lesions. A systematic review and meta-analysis of studies using Viabahn for popliteal artery aneurysms reported that the pooled primary and secondary patency rates were 69.4% and 77.4%, respectively, at 5 years, which seemed acceptable for anatomically suitable cases.²⁴ SUPERA was primarily used in popliteal artery lesions for bail-out of adverse events during percutaneous transluminal angioplasty, and the primary patency rates were reported to range from 68% to 90% at 1 year.^25–28

The practice of sitting on the floor or being cross-legged is common in some regions, including Japan. Accordingly, the effect of knee flexion needs to be critically evaluated in these regions. In the present study, the “kink”, which was rarely observed in the right-angled position, mimicking sitting on a chair, occurred in >30% of patients during maximum flexion, mimicking the position of sitting on the floor or sitting cross-legged. If EVT is performed on a popliteal lesion, it may be helpful to consider the patient’s lifestyle and advise minimizing frequent knee flexion for long-term patency. To the best of our knowledge, no studies to date have compared the patency of stents placed in isolated atherosclerotic popliteal arteries while considering race, lifestyle, and activity levels. Notably, making direct comparisons is challenging due to significant differences in patient backgrounds. Horie et al reported an 84.9% 12-month primary patency rate for patients treated with scaffolds (SUPERA, drug-eluting stent, or Viabahn) in isolated atherosclerotic popliteal arteries.²⁷ Furthermore, Salamaga et al reported primary patency rates ranging from 68% to 90% at 12 months after reviewing 4 studies conducted in Germany, Spain, and the US, where SUPERA implantation was performed in isolated popliteal arteries.²⁸ There were no significant differences in the prognosis of SUPERA/Viabahn placement in the popliteal artery among Europe, America, and Japan. This suggests that these scaffolds may possess sufficient kink resistance.

Drug-eluting devices have the advantage of increasing patency after EVT by reducing intimal thickening. Although a high patency rate has been reported, negative factors such as recurrence by thrombotic occlusion have also been reported.²⁹ Hemodynamics in the arterial lumen may affect intimal hyperplasia. In addition, high WSS and low OSI help limit the occurrence of atherosclerosis and intimal hyperplasia.^30,31 Our findings revealed lower minimum TAWSS and higher maximum OSI at sites of severe curvature around the AF and HP. This may indicate unfavorable sites for EVT considering long-term patency.

Sullivan et al reviewed the unique nitinol helical stent (BioMimics 3D helical centerline stent system; Veryan Medical, Horsham, UK), which induces a laminar swirling flow acting athero-protectively.³² Clinically, the use of this device in femoropopliteal lesions showed good 3-year outcomes, overall survival, freedom from major amputation rate, and clinically driven target lesion revascularization whether used alone or in combination with a drug-coated balloon.³³ From a hemodynamic perspective, drug-coated devices could be used to treat femoropopliteal lesions.

The present study had several limitations. First, the small number of patients may have been insufficient to evaluate the types of femoropopliteal artery deformation, including the HP, AP, and kink. Second, we did not consider the effects of arteriosclerotic changes in our arterial deformation analysis. In our opinion, arterial deformity in cases with wall calcification tends toward linearization. In this study, the analysis of blood flow parameters using TAWSS and OSI was restricted to 3 patients with poor calcification. Accordingly, it is necessary to evaluate the influence of calcification on the results in future studies.

Our study provides a definition of kink that is easy to understand and applicable in clinical practice. It may provide useful information for the placement of scaffolds in blood vessels. We aim to examine the influence of scaffolds, like stents, when kinks are present in future studies.

Conclusions

Our CT protocol during knee flexion revealed 3D morphological changes of the popliteal artery, including AF and HP. A “kink” could occur in the maximum flexion position; however, it rarely occurs in the right-angle flexion position. This may cause the outcomes of EVT for the popliteal lesion to vary by geographic region, such as in Japan, where individuals have a habit of bending their knees to the maximum flexion position. In addition, hemodynamic analysis revealed a tendency for a lower minimum WSS and higher maximum OSI at the maximum curvature of the popliteal artery, where the luminal condition should be unfavorable for EVT. In future studies, we aim to observe the changes in kinks when scaffolds are placed to verify the clinical significance of the occurrence of kinks.

Acknowledgments

The authors thank Editage (www.editage.jp) for English language editing. The authors also thank Taeka Kawakami for creating the illustrations in Figure 3. Finally, the authors thank all the radiologic technologists at the Department of Radiology, The University of Tokyo, who assisted with CT imaging examinations.

Sources of Funding

This research was funded by Otsuka Medical Devices Co., Ltd.

Disclosures

This study highlights the advantages of the BioMimics 3D Helical stent from Veryan Medical Limited, a member of the Otsuka Medical Devices group of companies and the study’s sponsor.

IRB Information

The study protocol was approved by the Institutional Research Ethics Committee of The University of Tokyo Hospital (Approval no. 2021196NI).

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