A comparative analysis of anatomical variations of popliteal artery and its branches in concomitant aneurysmal disease

Abstract

Objectives

Open or endovascular treatment of popliteal artery aneurysms (PAAs) is still debated. Data about the popliteal artery anatomy and its branches are essential to plan a surgical approach. The aim of this study was to report the anatomical variations of the popliteal artery and its branches in a population with aneurysmal disease and compare them with a standard population with non-aneurysmal disease.

Methods

A retrospective review of consecutive patients who underwent surgical PAA repair in our center between January 2011 and December 2020 was performed. One-hundred-forty-six limbs in 128 patients underwent PAA treatment (Group 1). Computed tomography angiography images using a 128-section configuration were reviewed for anatomical variations of the popliteal artery and its branches. A control population of 178 limbs in 89 patients with non-aneurysmal disease was used to compare the outcomes (Group 2). All limbs were classified according to Kim’s classification. The two groups were analyzed and compared by means of nonparametric Pearson chi-square test.

Results

Both groups were homogeneous in terms of demographics, risk factors, and clinical presentation. In Group 1, the limbs with PAA were classified as type IA, 133 (91.1%); type IB, 2 (1.4%); type IC, 0; type IIA1, 1 (0.7%); type IIA2, 1 (0.7%); type IIB, 4 (2.7%); type IIC, 0; type IIIA, 3 (2.1%); type IIIB, 0; and type IIIC, 2 (1.4%). In Group 2 the limbs with non-aneurysmal disease were classified as type IA, 163 (91.6%); type IB, 5 (2.8%); type IC, 1 (0.6%); type IIA1, 1 (0.6%); type IIA2, 3 (1.7%); type IIB, 2 (1.1%); type IIC, 0; type IIIA, 3 (1.7%); type IIIB, 0; and type IIIC, 0. No difference in terms of anatomy of the popliteal artery and its branches was found between the two groups (P = NS).

Conclusions

Knowledge of anatomical variations of the popliteal artery and its branches is mandatory in case of the surgical approach. Anatomy in PAA patients is not different. Studies with larger population size are needed to validate these outcomes.

Keywords

Popliteal artery aneurysm anatomical variation popliteal artery

Introduction

The popliteal artery is the direct prolongation of the superficial femoral artery into the popliteal fossa. According to standard anatomy, branches of the popliteal artery are the anterior tibial artery (ATA) and the tibioperoneal trunk which further divides into the posterior tibial artery (PTA) and the peroneal artery (PA).¹

The popliteal artery is the most common localization of peripheral aneurysms.² Some of them are related to muscular abnormalities.³

Open or endovascular treatment of popliteal artery aneurysms (PAAs) is still debated.^4,5 A recent metanalysis⁶ failed to demonstrate the superiority of endovascular techniques over open surgery in terms of graft thrombosis and reintervention rates.

Accurate preoperative evaluation including data concerning popliteal artery anatomy and its branches is crucial to plan a surgical approach.⁷ Digital subtraction angiography is the gold standard for the evaluation of anatomical variations.⁸ In the recent years, computed tomography angiography (CTA) reached high levels of sensitivity and specificity in detecting anatomical variations of the popliteal artery.^7,9,10

Knowledge of anatomy of the popliteal artery and its branches is mandatory when a surgical intervention in the knee region is performed. In case of total knee replacement or popliteal bypass/grafting, iatrogenic injuries with bleeding or ischemic complications could occur.¹¹

Kim et al.,¹² in 1989, published a modified classification system for the anatomy of the popliteal artery including three primary types and 10 subtypes. A recent metanalysis reported the data of about 12,757 lower limbs according to Kim’s classification.¹³ No mention about anatomical variations in PAAs has been made in the literature.

The aim of this study was to report the anatomical variations of the popliteal artery and its branches in a population with aneurysmal disease and compare them with a standard population with non-aneurysmal disease.

Materials and methods

Population study

A retrospective review of consecutive patients who underwent surgical PAA repair in our center between January 2011 and December 2020 was performed.

One-hundred-forty-six limbs in 127 patients underwent PAA treatment (Group 1). No patient had an entrapment syndrome.

A ghost population of 178 limbs in 89 patients with non-aneurysmal disease was used to compare the outcomes (Group 2).

Patients of Group 2 were randomly selected from our CT image database on OsiriX (Pixmeo SARL, Geneva, Switzerland) DICOM vascular software.

Institutional review board approval was waived. Patients undergoing surgical treatment gave their written consent to the procedure as approved by the ethics committee.

CT-scan

CT-images using a 128-section configuration were reviewed for anatomical variations of the popliteal artery and its branches.

Source images were processed using OsiriX (Pixmeo SARL, Geneva, Switzerland) DICOM vascular software. Transverse images were used to identify the ostia of popliteal branches. Moreover, maximum intensity projection (MIP), multiplanar reformatted (MPR) sections, and sagittal/coronal planes were used. If necessary, additional data were obtained with three-dimensional volume-rendered images.

Two vascular surgeons, one radiologist, and a technician simultaneously reviewed all CTA examinations in order to exclude interobserver variability.¹⁴ All examiners had more than 10 years of experience in interpretation of CTA images.

Kim’s classification

All limbs were classified according to Kim’s classification.¹² Figure 1 shows the anatomical patterns of the popliteal artery and its branches.

Figure 1.

Kim’s classification.

The presence of popliteal artery branches below the level of the knee joint were classified as type I, the presence of popliteal artery branches above the level of the knee joint were classified as type II, and any cases of hypoplastic/aplastic branches were classified as type III.

Type I included 3 variations

• Type IA: division into ATA and a common trunk for the PA and PTA

• Type IB: division into the ATA, PTA, and PA, all within 0.5 cm of each other

• Type IC: division into PTA and a common trunk of the ATA and PA

Type II included 4 variations

• Type IIA1: ATA originates first and follows a normal course

• Type IIA2: ATA originates first and follows a medial course (Figure 2)

• Type IIB: PTA originates first

• Type IIC: PA originates first

Figure 2.

Type IIA2 pattern: CT-scan images. green arrow, 40-mm popliteal artery aneurysm; red arrow, high origin of the anterior tibial artery.

Type III included 3 variations

• Type IIIA: hypoplasia or aplasia of PTA

• Type IIIB: hypoplasia or aplasia of ATA

• Type IIIC: hypoplasia or aplasia of PTA or ATA

Outcome measures and statistical analysis

All data were retrospectively collected in a dedicated database. Data included demographics, preoperative risk factors, clinical and diagnostic preoperative assessments, and intraoperative measurements (in case of surgery).

Continuous data were expressed as the mean ± range, and categoric data were expressed as percentages. Differences in outcomes between the groups (comparative analysis) were assessed using the nonparametric Pearson chi-square test. A post-hoc power analysis of the study was calculated (alpha error = 0.05).

Statistical significance was defined at the p < 0.05 level. Statistical analysis was performed using SPSS software (version 24.0 for Apple; IBM Corporation, Armonk, NY, USA).

Results

Both groups were homogeneous in terms of demographics and risk factors. A higher rate of symptomatic patients in terms of Rutherford class was detected in Group 1 (Table 1).

Table 1.

Demographic data and preoperative risk factors.

Demographics	Group 1 (128 pts)	Group 2 (89 pts)	P
Males	116 (90.6%)	83 (93.2%)	0.412
Age, y (range)	56–90	48–87	—
> 80 years	95 (74.2%)	65 (73%)	0.623
Risk factors
Smoking	38 (29.6%)	25 (28%)	0.513
Former smoker	80 (62.5%)	54 (60.6%)	0.525
Hypertension	110 (85.9%)	75 (84.2%)	0.634
Hypercholesterolemia	39 (30.4%)	26 (29.2%)	0.589
Diabetes mellitus	48 (37.5%)	41 (46%)	0.211
Coronary artery disease	25 (19.5%)	20 (22.4%)	0.521
Chronic renal failure^a	17 (13.2%)	12 (13.4%)	0.744
Dialysis treatment	1 (0.7%)	1 (1.1%)	0.248
Rutherford classification			0.04 (between asymptomatic and symptomatic patients)
0 (asymptomatic)	83 (64.8%)	64 (88.9%)
1–3 (claudication)	26 (20.3%)	6 (8.3%)
4 (rest pain)	10 (7.8%)	0
5 (minor tissue loss)	8 (6.2%)	2 (2.8%)
6 (major tissue loss)	0	0

Continuous data are presented as the mean; categorical data are given as the counts (percentage).

^aGlomerular filtration rate < 30 mL/min.

The post-hoc power of the study was 96.4% (alpha error = 0.05).

In Group 1, the limbs with PAA were classified as type IA, 133 (91.1%); type IB, 2 (1.4%); type IC, 0; type IIA1, 1 (0.7%); type IIA2, 1 (0.7%); type IIB, 4 (2.7%); type IIC, 0; type IIIA, 3 (2.1%); type IIIB, 0; and type IIIC, 2 (1.4%).

In Group 2, the limbs with non-aneurysmal disease were classified as type IA, 163 (91.6%); type IB, 5 (2.8%); type IC, 1 (0.6%); type IIA1, 1 (0.6%); type IIA2, 3 (1.7%); type IIB, 2 (1.1%); type IIC, 0; type IIIA, 3 (1.7%); type IIIB, 0; and type IIIC, 0.

No difference in terms of anatomy of popliteal artery and its branches was found between the two groups (Table 2).

Table 2.

Kim’s classification: Comparison of the two groups.

Type			Group 1 (146 limbs)	Group 2 (178 limbs)	Total (324 limbs)	P
I	A		133 (91.1%)	163 (91.6%)	296 (91.4%)	0.879
	B		2 (1.4%)	5 (2.8%)	7 (2.2%)	0.375
	C		—	1 (0.6%)	1 (0.3%)	0.364
II	A	1	1 (0.7%)	1 (0.6%)	2 (0.6%)	0.888
	A	2	1 (0.7%)	3 (1.7%)	4 (1.2%)	0.417
	B		4 (2.7%)	2 (1.1%)	6 (1.9%)	0.283
	C		—	—	—	—
III	A		3 (2.1%)	3 (1.7%)	6 (1.9%)	0.806
	B		—	—	—	—
	C		2 (1.4%)	—	2 (0.6%)	0.117

In Group 1, a concomitant abdominal aortic aneurysm was found in 35/128 patients (27.3%). In Group 2, an abdominal aortic aneurysm was present in 63 patients (70.8%).

Moreover, in Group 1, an open surgical approach was performed in the majority of limbs (117/146, 81.4%). In two cases, a selective reimplantation of the ATA on the venous bypass graft was performed. In three cases (2.1%), an endovascular exclusion of PAA was performed.

In Group 1 patients undergoing surgical treatment, no differences have been found in terms of 30-day outcomes (overall patency and limb salvage) in patients with type IA variation versus other variations.

The two patients undergoing selective reimplantation of the ATA on the venous bypass grafts had ATA patent at 13 and 27 months of follow-up, respectively.

Discussion

Anatomical variations of popliteal artery and its branches are well known. In the most comprehensive metanalysis published in the literature,¹³ type IA was the most common configuration with a prevalence of 92.6%. Another recent study⁸ (not included in this metanalysis) enrolling 1261 limbs reported type IA as the usual pattern with a prevalence of 88.7%. In the present study, the type IA pattern was found in 91.4% of all limbs analyzed.

Among variations, the most common pattern was type IB in Tomaszewski’s metanalysis¹³ (2.4%) and type IIIA in Demirtaş’ study⁸ (3.5%). In the present study, type IB was the common anatomical variation (2.2%).

Some differences could exist according to ethnicity. In an Asian population including 1242 extremities, the most common variation was type IIIA with the highest percentage reported in the literature (5.1%).¹⁵ This pattern was found in just 0.8% of 1037 lower limbs included in an angiographic study conducted in Europe.⁸ In the present study, type IIIA anatomical variation was detected in 1.9% of all included limbs.

Therefore, our comprehensive outcomes are very similar to Tomaszewski’s metanalysis¹³ and other studies reporting data about European population.^8,16,17

A key point could be the modality of diagnostic assessment. Some studies have been performed on cadavers.^18–20 However, these studies included a very limited number of lower limbs. In the past, arteriography was considered the gold standard to evaluate popliteal branching. Some studies^8,16 included more than 1000 lower extremities. More recently, CTA has been considered an effective method to evaluate popliteal artery anatomy and its branches.^8,10 Kil et al.¹⁵ used magnetic resonance imaging. Anecdotal studies reported color Doppler as modality of imaging to detect anatomical variations of the popliteal artery.^21,22

In the present retrospective study, we adopted CT-scan as modality of imaging assessment. The advantages of CTA were short examination time, high spatial resolution, and three-dimensional volume-rendered images.

Two vascular surgeons, one radiologist, and a technician simultaneously reviewed all CTA examinations. In case of doubts about occluded or hypoplastic/aplastic vessels, a second imaging analysis was planned after at least 1 week.

The control group included patients randomly selected from our CT image database. We usually perform a CT-scan of the abdomen and lower limbs in all patients with abdominal aortic aneurysm. Therefore, we have a lot of patients in our database with no peripheral arterial disease. For this reason, patients of both groups were homogeneous in terms of demographic data and risk factors but they differed in clinical presentation.

On the basis of our knowledge, no mention about anatomical variations in PAAs has been made in the literature.

Nevertheless, the post-hoc power of the study was high (96.4%); the study failed to demonstrate any differences in terms of anatomical variance between the two groups.

Indications and surgical approaches to PAAs are still debated. Surgery is mandatory in all symptomatic PAAs and in cases with a diameter bigger than 3 cm.^23,24 Open surgical repair of PAAs was associated with better outcomes than endovascular repair in terms of major adverse limb events and limb preservation.⁶ Superiority of the posterior approach over the medial approach for primary and secondary patency, aneurysm exclusion, and need for reoperation was noted in a recent metanalysis.²⁵

In case of surgical revascularization, run-off status (patency of below-the-knee vessels) significantly affected long-term outcomes in terms of patency and limb preservation.⁴ Therefore, when planning open or endo surgery for PAAs, it is very important to have knowledge about the anatomy of the popliteal artery and origins of the tibial vessels in order to preserve their patency in case of anatomical variations. In the present series in two cases, we performed surgical reimplantation of the ATA on the venous bypass graft. In both cases, patients had a high origin of ATA (type IIA1 and type IIA2 variations).

In the present comparative study, no difference in terms of anatomy of the popliteal artery and its branches was found in an aneurysmal or non-aneurysmal population. However, type II variations with high origins of tibial vessels could represent an issue in all planned interventions.

Even in orthopedic surgery, the knowledge of the popliteal anatomy and its branches should be considered when a surgical intervention is planned into the knee region. Major vascular injuries have been reported.²⁶ Type IIA1 and type IIA2 variations (high origin of ATA) are susceptible to a higher rate of potential bleeding complications during knee surgery.²⁰ This could account for litigations after knee surgery.²⁷

This study has some limitations. First, the study population is quite small. Second, the study is a retrospective analysis based on the assessments performed in a single center. Thirdly, the interobserver variability could be an issue even if the examination of CTA images was simultaneously performed by all the examiners.

Conclusions

Knowledge of anatomical variations of the popliteal artery and its branches is mandatory in cases of a surgical approach in the knee region. Anatomical variations in patients with aneurysmal disease are not different. Studies with larger population size are needed to validate these outcomes.

Footnotes

Authors’ contributions

Nicola Troisi, writing, data analysis, data interpretation, final revision, and final approval. Alberto Melani, writing, data collection, data analysis, figures, and final revision. Claudio Raspanti, data interpretation, final revision, and final approval. Simone Panci, data interpretation, final revision, and final approval. Emiliano Chisci, data interpretation, final revision, and final approval. Carlo Pratesi, final revision and final approval. Stefano Michelagnoli, final revision and final approval.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Nicola Troisi

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