Popliteal artery aneurysm

Anne Cervin*¹, Igor Koncar*² and Martin Björck³

*AC and IK are joint first authors of this chapter.

¹ Dep of Hybrid and Intervention, Sahlgrenska University Hospital, Gothenburg, Sweden
² Faculty of Medicine, University of Belgrade, Serbia
³ Department of Surgical Sciences, University of Uppsala, Sweden

Corresponding author: Igor Koncar, Faculty of Medicine, University of Belgrade, Serbia

Email address: Dr.koncar@gmail.com

Seven decades ago, Gifford described popliteal artery aneurysm (PAA) as a “sinister harbinger of sudden catastrophe” and it still is. Despite being the most common peripheral aneurysm, PAA is often marginalized, despite that it can result in very serious consequences. Symptomatic PAA presents with various clinical manifestations; thrombosis, distal embolization, compression of surrounding veins or nerves, as well as rupture. The risk of amputation in symptomatic patients is high, justifying prophylactic surgery.

Once a PAA is detected, multiple dilemmas arise. Defining the exact indication for treatment is difficult. For now, the diameter and presence of thrombus are both assessed. Surgical technique for treating and excluding the aneurysm includes open or endovascular techniques, but there are several aspects to consider. Open surgery is more invasive but provides good early and long-term results. When open surgery is planned, the selection of medial or dorsal approach, as well as the choice of conduit, depends on anatomy, morphology of the PAA and availability of autologous vein with sufficient diameter. Endovascular treatment is improving. The biomechanics of the popliteal artery, affected by the bending of the knee, combined with the low flow at rest, are important challenges and explain why endovascular technology has developed less quickly compared to for AAA. In symptomatic patients, the state of the patient and degree of ischaemia need to be evaluated before deciding whether thrombolysis, endovascular thrombectomy, direct open surgery, or a combination of these techniques, is the best option.

This chapter presents comprehensive data on epidemiology, clinical presentation, and natural history of PAA, as well as recommendations for optimal diagnostic work-up in both symptomatic and asymptomatic patients. Treatment modalities and their respective results are presented. Suggestions for future research are also given, hoping that the scientific challenge to improve future treatment of this disease are accepted.

The popliteal artery is created from the union of two arteries, during foetal life. The deep popliteal artery originates from the sciatic system initially supplying the blood to the lower leg, and the superficial popliteal artery, that develops later. In a patient with normal anatomy, the popliteal artery is defined as originating where the superficial femoral artery (SFA) passes through the adductor hiatus (also named the Hunter’s canal) to where the vessel branches into the anterior tibial artery and the tibio-peroneal trunk, as shown in Figure 1. The popliteal artery passes through the popliteal fossa, which also contains the popliteal vein, the small saphenous vein, the common peroneal and tibial nerves, the posterior cutaneous nerve of the thigh, the genicular branch of the obturator nerve, connective tissue, and lymph nodes. This is a confined space limited by tendons and muscles. Morphological changes of the vessel will occur during knee flexion. There are changes in length, curvature, angulation and torsion ¹Klein AJ, Chen SJ, Messenger JC, Hansgen AR, Plomondon ME, Carroll JD, et al. Quantitative assessment of the conformational change in the femoropopliteal artery with leg movement. Catheter Cardiovasc Interv 2009; 74: 787-798.,²Wensing PJ, Scholten FG, Buijs PC, Hartkamp MJ, Mali WP and Hillen B. Arterial tortuosity in the femoropopliteal region during knee flexion: a magnetic resonance angiographic study. J Anat 1995;187( Pt 1):133-139. In healthy individuals, the movement and angulation of the vessel will be most pronounced between the areas where the vessel is fixed: Hunter’s canal and the origin of anterior tibial artery.

Figure 1. The surgical anatomy of the popliteal artery is presented in these reconstructed images of MDCT angiography. The popliteal artery starts at the level of the adductor hiatus and ends at the origin of the first crural vessel (in most cases the anterior tibial artery).

There are very few studies on the prevalence of PAA in the healthy population. In a paper from 2002 it was estimated to occur in approximately 1% of men in the age interval 65-80 years¹Trickett JP, Scott RAP and Tilney HS. Screening and management of asymptomatic popliteal aneurysms. Journal of Medical Screening 2002; 9: 92-93.. There is no consensus how to define a PAA, and as a consequence, a number of definitions are suggested: 15 or 19 mm in diameter²Trickett JP, Scott RAP and Tilney HS. Screening and management of asymptomatic popliteal aneurysms. Journal of Medical Screening 2002; 9: 92-93.,³Tuveson V, Lofdahl HE and Hultgren R. Patients with abdominal aortic aneurysm have a high prevalence of popliteal artery aneurysms. Vasc Med 2016; 21: 369-375.,⁴Cervin A, Wanhainen A, Bjorck M. Popliteal Aneurysms are Common Among Men With Screening Detected Abdominal Aortic Aneurysms, and Prevalence Correlates With the Diameters of the Common Iliac Arteries. Eur J Vasc Endovasc Surg 2020; 59: 67-72.,⁵Diwan A, Sarkar R, Stanley JC, et al. Incidence of femoral and popliteal artery aneurysms in patients with abdominal aortic aneurysms. J Vasc Surg 2000; 31: 863-869., 50% larger than a normal diameter⁶Trickett JP, Scott RAP and Tilney HS. Screening and management of asymptomatic popliteal aneurysms. Journal of Medical Screening 2002; 9: 92-93.,⁷Cervin A, Wanhainen A, Bjorck M. Popliteal Aneurysms are Common Among Men With Screening Detected Abdominal Aortic Aneurysms, and Prevalence Correlates With the Diameters of the Common Iliac Arteries. Eur J Vasc Endovasc Surg 2020; 59: 67-72., 50% larger than the adjacent vessel (i.e. the distal superficial femoral artery, SFA) or 50% larger than the contralateral, non-aneurysmal popliteal artery⁸Cervin A, Wanhainen A, Bjorck M. Popliteal Aneurysms are Common Among Men With Screening Detected Abdominal Aortic Aneurysms, and Prevalence Correlates With the Diameters of the Common Iliac Arteries. Eur J Vasc Endovasc Surg 2020; 59: 67-72.,⁹Diwan A, Sarkar R, Stanley JC, et al. Incidence of femoral and popliteal artery aneurysms in patients with abdominal aortic aneurysms. J Vasc Surg 2000; 31: 863-869.,¹⁰Johnston KW, Rutherford RB, Tilson MD, et al. Suggested standards for reporting on arterial aneurysms. Subcommittee on Reporting Standards for Arterial Aneurysms, Ad Hoc Committee on Reporting Standards, Society for Vascular Surgery and North American Chapter, International Society for Cardiovascular Surgery. J Vasc Surg 1991; 13: 452-458.,¹¹Grip O, Mani K, Altreuther M, et al. Contemporary Treatment of Popliteal Artery Aneurysms in 14 Countries: A Vascunet Report. Eur J Vasc Endovasc Surg 2020; 60: 721-729.. It is unknown, however, how the risk of future complications and growth of the PAA are associated with these different definitions.The number of PAA repairs varies between countries. An assessment of thirteen countries participating in the Vascunet collaboration, and having data on PAA, showed a range of operations between 2.4 and 19.3 per million inhabitants per year during 2012-2018 ¹²Grip O, Mani K, Altreuther M, et al. Contemporary Treatment of Popliteal Artery Aneurysms in 14 Countries: A Vascunet Report. Eur J Vasc Endovasc Surg 2020; 60: 721-729.. This report also demonstrated the great differences in indications for surgery: emergency, elective symptomatic or asymptomatic. In Serbia, 17% were emergency procedures, while in Norway the same figure was 31%.

Pseudoaneurysm is a dilation of an artery caused by injury to one or more layers of the artery. The popliteal artery can be injured during an accident (e.g. fracture or dislocation of the knee area) or secondary to surgical trauma (e.g. catheterisation or during knee surgery ¹³Bernhoff K and Bjorck M. Iatrogenic popliteal artery injury in non arthroplasty knee surgery. Bone Joint J 2015; 97-B: 192-196.,¹⁴Bernhoff K, Rudstrom H, Gedeborg R, et al. Popliteal artery injury during knee replacement: a population-based nationwide study. Bone Joint J 2013; 95-B: 1645-1649.. It is important to single out true from the false aneurysms, as the fundamental mechanisms for complications and choice of treatment, are different.

PAAs are associated with multi-aneurysm disease (arteriomegaly, arterial ectasia). At presentation, bilateral PAAs are present in 46-68% and a concomitant AAA in 33-40% ¹⁵Vermilion, B. D., S. A. Kimmins, W. G. Pace and W. E. Evans. A review of one hundred forty-seven popliteal aneurysms with long-term follow-up. Surgery 1981;90:1009-1014.,¹⁶Varga, Z. A., J. C. Locke-Edmunds and R. N. Baird. A multicenter study of popliteal aneurysms. Joint Vascular Research Group. J Vasc Surg 1994; 20: 171-177.. Patients with bilateral PAAs have a higher frequency of AAA than those with unilateral PAA ¹⁷Vermilion, B. D., S. A. Kimmins, W. G. Pace and W. E. Evans. A review of one hundred forty-seven popliteal aneurysms with long-term follow-up. Surgery 1981;90:1009-1014.,¹⁸Ravn, H., D. Bergqvist and M. Bjorck. Nationwide study of the outcome of popliteal artery aneurysms treated surgically. Br J Surg 2007:94; 970-977.. Some population-based screening programmes have established a routine to add a measurement of the popliteal artery at re-examination of the enlarged aorta.

Most PAA are asymptomatic. PAA can, however, cause acute limb ischaemia (ALI) or critical limb ischaemia (CLI) either by thrombosis/occlusion of the aneurysm itself, and/or by embolization to the vessels below ¹Ravn H, Björck M. Popliteal artery aneurysm with acute ischemia in 229 patients. Outcome after thrombolytic and surgical therapy.Eur J Vasc Endovasc Surg. 2007;33:690-5.. Depending on collaterals and the extent of the occlusion, symptoms range between temporary pain from embolization that resolves, to occlusion with sudden claudication or severe ALI, that needs prompt revascularisation.

Ruptured PAA (rPAA) is a rare event, and in the literature, mostly case reports are found ²Vermilion, B. D., S. A. Kimmins, W. G. Pace and W. E. Evans. A review of one hundred forty-seven popliteal aneurysms with long-term follow-up. Surgery 1981;90:1009-1014.,³Roggo A, Hoffmann R, Duff C, Brunner U, Largiader F. How often does an aneurysm of the popliteal artery rupture?. Helv Chir Acta 1993: 145-148.,⁴Sie RB, Dawson I, van Baalen JM, Schultze Kool LJ, van Bockel JH. Ruptured popliteal artery aneurysm. An insidious complication. Eur J Vasc Endovasc Surg 1997: 432-438., with the exception of a national series of 45 legs with rPAA ⁵Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758.. Large aneurysms can compress the adjacent vein or nerves which may cause a slowly increasing swelling of the lower leg and sometimes deep venous thrombosis (DVT) as well as neuralgia of the calf and foot ⁶Haaverstad R, Fougner R and Myhre HO. Venous haemodynamics and the occurrence of leg oedema in patients with popliteal aneurysm. Eur J Vasc Endovasc Surg 1995: 204-210.,⁷Beaudry Y, Stewart JD and Errett L. Distal sciatic nerve compression by a popliteal artery aneurysm. Can J Neurol Sci 1989: 352-353.,⁸Logigian EL, Berger AR and Shahani BT. Injury to the tibial and peroneal nerves due to hemorrhage in the popliteal fossa. Two case reports. J Bone Joint Surg Am 1989: 768-770..

During the 1970s and 1980s, there was a debate whether a conservative or a more aggressive surgical approach was appropriate for patients with asymptomatic PAA. When presenting with acute ischaemic symptoms, there was a high rate of amputation: 13-36% ¹Vermilion, B. D., S. A. Kimmins, W. G. Pace and W. E. Evans. A review of one hundred forty-seven popliteal aneurysms with long-term follow-up. Surgery 1981;90:1009-1014.,²Ravn H, Björck M. Popliteal artery aneurysm with acute ischemia in 229 patients. Outcome after thrombolytic and surgical therapy.Eur J Vasc Endovasc Surg. 2007;33:690-5.,³Wychulis AR, Spittel JA, Wallace RB. Popliteal aneurysms. Br J Surg 1974,61:469-75.,⁴Whitehouse WM, Wakefield L, Graham JM et al. Limb-threating potential of atherosclerotic popliteal artery aneurysms. Surgery 1983, 93:694-9.,⁵Lowell RC, Gloviczki P, HallettJW Jr., Naessens JM, Maus TP, CherryKJ Jr., et al. Popliteal artery aneurysms: the risk of nonoperative management. Ann Vasc Surg 1994;8:14-23.. In earlier studies, patients with asymptomatic PA were managed conservatively more often, and developed symptoms in 29-60%, see Table 1. There was, and still is, a higher risk of amputation in patients treated as an emergency, both in the acute phase, and later, due to inferior patency at follow-up ⁶Anton G, Hertzer N, Beven E, O’Hara P, Krajewski L. Surgical management of popliteal aneurysms. J Vasc Surg. 1986; 3: 125-134.,⁷Schellack J, Smith RB 3^rd, Perdue G D. Nonoperative management of selected popliteal aneurysms. Arch Surg 1987: 122: 372-375.,⁸Huang Y., Gloviczki P, Oderich GS, Duncan AA, Kalra M, Fleming MD, et al. Outcomes of endovascular and contemporary open surgical repairs of popliteal artery aneurysm.2014;J Vasc Surg 60: 631-638.. A more active approach became accepted. The criteria to justify intervention remain controversial. PAA size is easily measured and has some correlation with risk of thrombosis, but other mechanisms are poorly understood. Concerning PAA rupture, logically, size should reflect the risk. Rupture, however, is the indication for repair in only 2–4% of PAA treated ⁹Ravn, H., D. Bergqvist and M. Bjorck. Nationwide study of the outcome of popliteal artery aneurysms treated surgically. Br J Surg 2007:94; 970-977.,¹⁰Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758.. In most studies, diameter less than 2 cm is associated with a lower incidence of complications, 0–9% ¹¹Whitehouse WM, Wakefield L, Graham JM et al. Limb-threating potential of atherosclerotic popliteal artery aneurysms. Surgery 1983, 93:694-9.,¹²Lowell RC, Gloviczki P, HallettJW Jr., Naessens JM, Maus TP, CherryKJ Jr., et al. Popliteal artery aneurysms: the risk of nonoperative management. Ann Vasc Surg 1994;8:14-23.,¹³Schellack J, Smith RB 3^rd, Perdue G D. Nonoperative management of selected popliteal aneurysms. Arch Surg 1987: 122: 372-375.. Although acute complications do occur in patients with small PAA ¹⁴Ravn, H., D. Bergqvist and M. Bjorck. Nationwide study of the outcome of popliteal artery aneurysms treated surgically. Br J Surg 2007:94; 970-977.,¹⁵Ascher, E., N. Markevich, R. W. Schutzer, S. Kallakuri, T. Jacob and A. P. Hingorani. Small popliteal artery aneurysms: are they clinically significant? 2003;J Vasc Surg 37: 755-760., Galland and Magee reported that a diameter ≥3cm, in combination with an angulation of more than 45 degrees, was strongly associated with thrombosis and ALI ¹⁶Galland, R. B. and T. R. Magee. Popliteal aneurysms: distortion and size related to symptoms. 2005; Eur J Vasc Endovasc Surg 30: 534-538.. In summary, risk factors for acute complications of PAA are not yet identified with sufficient precision, but there is an association between increasing size and the risk of ALI.

The diagnostic work up of a patient with suspected PAA, presented in Table 2, has several objectives: to verify the diagnosis, explore the presence of symptoms and assess the aneurysm morphology (diameter, extension, presence of thrombosis).

A PAA may be identified by careful clinical examination, but estimating the size may be difficult, and must be verified (or excluded) by imaging, usually Duplex ultrasound (DUS). DUS may also be used for screening, usually men with an AAA, where the incidence is higher ¹Schellack J, Smith RB 3^rd, Perdue G D. Nonoperative management of selected popliteal aneurysms. Arch Surg 1987: 122: 372-375.. It is recommended PAA should be sought by DUS in every patient diagnosed with, or previously operated on for AAA, especially in those with wide common iliac arteries ²Cervin A, Wanhainen A, Bjorck M. Popliteal Aneurysms are Common Among Men With Screening Detected Abdominal Aortic Aneurysms, and Prevalence Correlates With the Diameters of the Common Iliac Arteries. Eur J Vasc Endovasc Surg 2020; 59: 67-72..

Diameter and morphology of the PAA are crucial for decision-making when risk of complications is balanced against the risk of the procedure. PAA is an aneurysm with low risk of rupture, but high risk of thrombosis and distal embolization. Consequently, besides diameter, thrombus volume/diameter and morphology are useful imaging parameters, since they correlate with the risk of distal embolization and thrombosis ³Lowell RC, Gloviczki P, HallettJW Jr., Naessens JM, Maus TP, CherryKJ Jr., et al. Popliteal artery aneurysms: the risk of nonoperative management. Ann Vasc Surg 1994;8:14-23.,⁴A. Farber, N. Angle, E. Avgerinos, L. Dubois, M. Eslami, P. Geraghty, et al. The Society for Vascular Surgery clinical practice guidelines on popliteal artery aneurysms J Vasc Surg 2022;75(1):109-120..

Once intervention has been agreed, a more detailed mapping of the popliteal artery is necessary to plan the treatment. Computed tomography angiography (CTA) is the standard for obtaining such information, including evaluation of the run off. DUS still has an important role for planning an open surgical repair (OSR), providing information about the diameter and quality of great and small saphenous vein for bypass and marking the anatomy of the vein and the PAA. If open repair by the posterior approach is planned ⁵Morris-Stiff G, Haynes M, Ogunbiyi S, Townsend E, Shetty S, Winter RK, et al. Is assessment of popliteal artery diameter in patients undergoing screening for abdominal aortic aneurysms a worthwhile procedure. Eur J Vasc Endovasc Surg. 2005;30:71-4., the surgeon should consider being present in the vascular laboratory or ultrasound mapping of the extent of the PAA themself. The adductor canal (Hunter’s canal) can be reached from behind, even 20 cm above the knee joint. Since it is deep, however, marking the exact location of the upper limit of the PAA minimizes the dissection.

Preoperative measurement of Ankle Brachial Index (ABI) provides more information about limb and foot perfusion which is helpful in assessment of the severity of ischaemia, and which of the crural arteries are still open.

In a patient with ALI due to PAA, additional diagnostic considerations are required. The duration of ischaemia is of particular importance and should be correlated with the clinical status. The “six hours” rule describing the time needed to develop irreversible ischaemia should be considered, but in real life it often takes longer for this to develop due to existing collaterals. The presence of motor and sensory impairment, and pain on calf squeezing if muscle necrosis has developed, may obviate revascularisation, and sometimes primary amputation is the only option. Clinical examination is crucial!

Open versus endovascular treatment of PAA

Open surgical repair (OSR) with a vein interposition graft or bypass remains the first option for treatment of PAA. Treatment with a stent graft (endovascular repair, ER) might be considered for frail patients. A prosthetic graft or an ER can be considered for those with no adequate vein. The morphology of the popliteal vessel should be taken into consideration and the risk of complications after treatment should be weighed against the benefits of a minimally invasive treatment.

Results after OSR for PAA are well studied. Independent risk factors for occlusion and amputation are emergency procedures and the use of a prosthetic bypass graft¹Huang Y, Gloviczki P, Noel AA, Sullivan TM, Kalra M, Gullerud RE, et al. Early complications and long-term outcome after open surgical treatment of popliteal artery aneurysms: is exclusion with saphenous vein bypass still the gold standard? J Vasc Surg. 2007;45:706-13; discussion 13-5,²Ravn H, Wanhainen A, Bjorck M. Surgical technique and long-term results after popliteal artery aneurysm repair: results from 717 legs. J Vasc Surg. 2007;46:236-43.. There is a risk of wound complications, especially after emergency procedures, but operative mortality is low, even in high-risk patients ³Johnson ON, 3rd, Slidell MB, Macsata RA, Faler BJ, Amdur RL, Sidawy AN. Outcomes of surgical management for popliteal artery aneurysms: an analysis of 583 cases. J Vasc Surg. 2008;48:845-51. Four-year secondary patency rates of 84% – 97% have been reported.⁴Schwarze V, Marschner C, de Figueiredo GN, Rübenthaler J, Clevert DA. Contrast-enhanced ultrasound (CEUS) in the diagnostic evaluation of popliteal artery aneurysms, a single-center study. Clin Hemorheol Microcirc. 2020;76:191-197.,⁵Kropman RH, van Santvoort HC, Teijink J, van de Pavoordt HD, Belgers HJ, Moll FL, et al. The medial versus the posterior approach in the repair of popliteal artery aneurysms: a multicenter case-matched study. J Vasc Surg. 2007;46:24-30.,⁶Dorweiler B, Gemechu A, Doemland M, Neufang A, Espinola-Klein C, Vahl CF. Durability of open popliteal artery aneurysm repair. J Vasc Surg. 2014;60(4):951-7.

The patency is dependent on the availability of a vein conduit for bypass. The great saphenous vein (GSV) on both legs should be evaluated preoperatively with DUS. The evaluation includes the vein’s diameter, quality, and available length. Generally, veins >3 mm in diameter are adequate⁷Wengerter KR, Veith FJ, Gupta SK, Ascer E, Rivers SP. Influence of vein size (diameter) on infrapopliteal reversed vein graft patency. J Vasc Surg. 1990;11:525-31., and veins above 2.5 mm are worthy of exploration⁸Slim H, Tiwari A, Ritter JC, Rashid H. Outcome of infra-inguinal bypass grafts using vein conduit with less than 3 millimeters diameter in critical leg ischemia. J Vasc Surg. 2011;53:421-5.. In patients with PAA, however, the arteries are usually quite wide, and even a 3 mm vein may result in considerable mismatch. If a 4-5 mm vein is available, that is ideal. If there is doubt that the GSV is good enough, the SSV and arm veins should be considered. A shorter vein may be needed if the posterior approach is used, or by tunneling the vein anatomically from above to below the knee. Using a duplicating vein is not advisable for PAA since there is a risk of developing vein graft aneurysms⁹Ravn H, Wanhainen A, Bjorck M. Surgical technique and long-term results after popliteal artery aneurysm repair: results from 717 legs. J Vasc Surg. 2007;46:236-43..

Endovascularly, a polytetraflouroethylene graft secured with a Palmaz stents was first used to treat an asymptomatic PAA in 1994¹⁰Marin ML, Veith FJ, Panetta TF, Cynamon J, Bakal CW, Suggs WD, et al. Transfemoral endoluminal stented graft repair of a popliteal artery aneurysm. J Vasc Surg. 1994;19:754-7. As the technique has evolved, so have the stent grafts and the most commonly used stent graft is Viabahn, (GORE^®) a self-expandable stent graft with high radial force and flexibility. The latest generation has heparin bonded to the inner surface and is the most frequently used stent graft in later studies. The procedure is minimally invasive, performed under local anaesthesia and requires short hospital stay.

Direct comparison between results after open and endovascular surgery is difficult due to selection bias in indications, run-off, patient age and comorbidities.

In two large studies comparing ER with OSR for PAA, the groups were markedly different with 2.5-3 times more patients with acute ischaemia, as well as poor run-off, in the OSR group¹¹Pulli R, Dorigo W, Castelli P, Dorrucci V, Ferilli F, De Blasis G, et al. A multicentric experience with open surgical repair and endovascular exclusion of popliteal artery aneurysms. Eur J Vasc Endovasc Surg. 2013;45:357-63.,¹²Leake AE, Avgerinos ED, Chaer RA, Singh MJ, Makaroun MS, Marone LK. Contemporary outcomes of open and endovascular popliteal artery aneurysm repair. J Vasc Surg. 2016;63:70-6.. In the study of Pulli et al, primary and secondary patencies were similar, but 63% of the OSRs were done with a prosthetic graft¹³Pulli R, Dorigo W, Castelli P, Dorrucci V, Ferilli F, De Blasis G, et al. A multicentric experience with open surgical repair and endovascular exclusion of popliteal artery aneurysms. Eur J Vasc Endovasc Surg. 2013;45:357-63.. In Leake et al, primary patency still favoured OSR even though secondary patency rates were comparable¹⁴Leake AE, Avgerinos ED, Chaer RA, Singh MJ, Makaroun MS, Marone LK. Contemporary outcomes of open and endovascular popliteal artery aneurysm repair. J Vasc Surg. 2016;63:70-6..

Similar selection bias and results were reported in a meta-analysis from 2017, including 14 studies and 4,500 treated PAAs¹⁵Leake AE, Segal MA, Chaer RA, Eslami MH, Al-Khoury G, Makaroun MS, et al. Meta-analysis of open and endovascular repair of popliteal artery aneurysms. J Vasc Surg. 2017;65:246-56. For OSR, the weighted mean for primary patency at 1 year and 3 years was 88.3% and 79.4%, whereas the secondary patency was 92.3% and 86.6%. For ER, the primary patency at 1 year and 3 years was 81.2% and 68.2%, whereas the secondary patency was 86.3% and 80.0%, respectively.

In a recent publication¹⁶Cervin A, Acosta S, Hultgren R, Grip O, Bjorck M, Falkenberg M. Results After Open and Endovascular Repair of Popliteal Aneurysm: A Matched Comparison Within a Population Based Cohort. Eur J Vasc Endovasc Surg. 2021;61:988-97, with comparable groups matched for indication and outflow, the Hazard Ratio for permanent graft occlusion in ER compared with OSR was 2.47 (1.35-4.50), p=0.003. This, however, might reflect the high proportion of patients treated for acute ischaemia (32%), a factor that is highlighted repeatedly as an independent risk factor for adverse events and occlusions after ER¹⁷Leake AE, Avgerinos ED, Chaer RA, Singh MJ, Makaroun MS, Marone LK. Contemporary outcomes of open and endovascular popliteal artery aneurysm repair. J Vasc Surg. 2016;63:70-6.,¹⁸Leake AE, Segal MA, Chaer RA, Eslami MH, Al-Khoury G, Makaroun MS, et al. Meta-analysis of open and endovascular repair of popliteal artery aneurysms. J Vasc Surg. 2017;65:246-56,¹⁹Cervin A, Acosta S, Hultgren R, Grip O, Bjorck M, Falkenberg M. Results After Open and Endovascular Repair of Popliteal Aneurysm: A Matched Comparison Within a Population Based Cohort. Eur J Vasc Endovasc Surg. 2021;61:988-97,²⁰Trinidad-Hernandez M, Ricotta JJ, 2nd, Gloviczki P, Kalra M, Oderich GS, Duncan AA, et al. Results of elective and emergency endovascular repairs of popliteal artery aneurysms. J Vasc Surg. 2013;57:1299-305.,²¹Huang Y, Gloviczki P, Oderich GS, Duncan AA, Kalra M, Fleming MD, et al. Outcomes of endovascular and contemporary open surgical repairs of popliteal artery aneurysm. J Vasc Surg. 2014;60:631-8.,²²Maraglino, C., G. Canu, R. Ambrosi, F. Briolini, R. Gotti, P. Cefali, F. et al. Ferrero and F. Terraneo. Endovascular Treatment of Popliteal Artery Aneurysms: A Word of Caution after Long-Term Follow-up. Ann Vasc Surg 2017;41: 62-68..

The only RCT comparing OSR vs. ER was small, 30 patients, included only asymptomatic PAs, reporting no difference in patency at one year (primary 100 vs 86.7%, secondary patency 100 % in both groups)²³Antonello M, Frigatti P, Battocchio P, Lepidi S, Cognolato D, Dall’Antonia A, et al. Open repair versus endovascular treatment for asymptomatic popliteal artery aneurysm: results of a prospective randomized study. J Vasc Surg. 2005;42:185-93..

This variability in results may be one of the major reasons why there is wide variation in the uptake of stent grafts between hospitals and countries. In a recent Vascunet report²⁴Grip O, Mani K, Altreuther M, et al. Contemporary Treatment of Popliteal Artery Aneurysms in 14 Countries: A Vascunet Report. Eur J Vasc Endovasc Surg 2020; 60: 721-729., in New Zealand, 42% of the elective PAAs were treated with a stent graft, while in in Denmark, no stent grafts were used.

Still, treatment with a stent graft has good results in many studies and there are several benefits with the minimally invasive treatment for frail patients. But unlike open surgery, the risk factors for adverse events and occlusion after ER, are not clear. Further studies are warranted, but the following factors are worth to evaluate when considering ER:

1. Run-off. Poor run-off has more impact on patency after ER than OSR²⁵Cervin A, Acosta S, Hultgren R, Grip O, Bjorck M, Falkenberg M. Results After Open and Endovascular Repair of Popliteal Aneurysm: A Matched Comparison Within a Population Based Cohort. Eur J Vasc Endovasc Surg. 2021;61:988-97,²⁶Garg K, Rockman CB, Kim BJ, Jacobowitz GR, Maldonado TS, Adelman MA, et al. Outcome of endovascular repair of popliteal artery aneurysm using the Viabahn endoprosthesis. J Vasc Surg. 2012;55:1647-53,²⁷Rich NM. Popliteal entrapment and the posterior approach to the popliteal artery. In. Greenhalgh RM (ed). Vascular and endovascular surgical techniques 3rd Edition 1994, WB Saunders Company, Philadelphia, London, Sydney, Toronto pp330-4..
2. Diameter of the distal popliteal artery. In a population-based cohort, matched for indication, small stent graft diameter (median 7 mm) was associated with higher risk of occlusion after ER²⁸Cervin A, Acosta S, Hultgren R, Grip O, Bjorck M, Falkenberg M. Results After Open and Endovascular Repair of Popliteal Aneurysm: A Matched Comparison Within a Population Based Cohort. Eur J Vasc Endovasc Surg. 2021;61:988-97 The importance of the diameter is consistent with previous observations after stent graft treatment for chronic occlusive disease in the SFA and a need for oversizing in a small vessel²⁹Saxon RR, Chervu A, Jones PA, Bajwa TK, Gable DR, Soukas PA, et al. Heparin-bonded, expanded polytetrafluoroethylene-lined stent graft in the treatment of femoropopliteal artery disease: 1-year results of the VIPER (Viabahn Endoprosthesis with Heparin Bioactive Surface in the Treatment of Superficial Femoral Artery Obstructive Disease) trial. J Vasc Interv Radiol. 2013;24:165-73; quiz 74.
3. In an elongated aneurysmal artery, the morphological changes normally occurring during knee-flexion may be enhanced and lead to kinking at the end of the stent graft³⁰Rich NM. Popliteal entrapment and the posterior approach to the popliteal artery. In. Greenhalgh RM (ed). Vascular and endovascular surgical techniques 3rd Edition 1994, WB Saunders Company, Philadelphia, London, Sydney, Toronto pp330-4. and higher risk of occlusion. A technical suggestion is to do an angiogram with a bent knee, before deploying the stent graft to evaluate popliteal artery curvature points, and after, to check for kinking and need for extension³¹Piazza M, Menegolo M, Ferrari A, Bonvini S, Ricotta JJ, Frigatti P, et al. Long-term outcomes and sac volume shrinkage after endovascular popliteal artery aneurysm repair. Eur J Vasc Endovasc Surg. 2014;48:161-8. If pronounced tortuosity with straight or bent leg, OSR is recommended (see image below).
4. Use of an ER for a symptomatic PAA with acute ischaemia is an independent risk factor for poor patency.
5. The patient must be able to take dual antiplatelet therapy (DAPT)³²Tielliu IF, Verhoeven EL, Zeebregts CJ, Prins TR, Span MM, van den Dungen JJ. Endovascular treatment of popliteal artery aneurysms: results of a prospective cohort study. J Vasc Surg. 2005;41:561-7. (read more here) after ER, or Aspirin with low dose Rivaroxaban.

Surgical tips and planning for ER of PAA

Access is established via the common femoral artery. The choice between antegrade or retrograde puncture depends on the anatomy. As the stent graft requires a quite large introducer, the feasibility for a suitable closure device should be considered, or a cut down planned. The PAA is crossed, and an appropriately stiff guide wire is placed distal to the aneurysm. The stent graft used should have good radial strength and high flexibility – the one most commonly used is Gore Viabahn® Endoprosthesis.

According to manufacturer’s instructions for use (IFU), there should be a proximal and distal landing-zone of at least 20 mm and if two or more stent grafts are used, an overlap of at least 20 mm. General recommendation for the Viabahn is to use a stent graft diameter 5–20% larger than the healthy vessel diameter; in PAAs it is preferable to use less oversizing within that range. Preoperative assessment of anatomy in straight and bended knee is very important, as shown in Figure 2.

There are no tapered Viabahn stent grafts, and if stent grafts of different sizes are used, the stent graft with larger diameter should be telescoped into the stent graft with a smaller diameter. The diameter of two overlapping stent grafts should not vary more than 1 mm and overlapping should be avoided at the points of flexion in the vessel.

Figure 2. This male patient aged 44 years had acute occlusion of a PAA. After thrombolysis, angiogram images were taken with both straight (left) and bent knee (right). There was a pronounced tortuosity with a bent knee. He was treated with vein graft in open surgery with posterior approach.

 Once open repair is considered as treatment option there are several important decisions to make, as presented in Table 3 and in more detailed discussed in the text below.

Surgical approach

The surgical approach should provide simultaneous access to both proximal and distal healthy arterial sections, control the aneurysm, and enable thrombectomy of all three crural arteries. As shown in Table 3, neither dorsal nor medial approaches provide all of the above in every case, and an individualized approach to each patient is required.

Dorsal (posterior) approach

The dorsal approach is performed with the patient in prone position. It is preferable that the surgeon has mapped the patient with DUS before the patient enters the OR. The upper limit of the PAA is marked so that the surgeon feels confident that it can be reached from behind. The vein to harvest is also marked. The GSV often has a sufficient diameter when it passes the knee joint, which is accessible in the prone position, from the same or the contralateral side, in particular if the patient leg is slightly tilted to the lateral side. The SSV vein may also be considered, although unfortunately its diameter is seldom large enough. An alternative solution is a ringed ePTFE or a Dacron graft.

The skin incision should be S-shaped to minimize the risk of scarring in the hollow of the knee. The dissection has to be performed with great precision to avoid injury to the nerves and veins. Be careful with the retractors! After the arteries have been clamped above and below the PAA the aneurysm is opened longitudinally, the thrombus is removed and the back bleeding from the branches is secured with suture ligatures. The interposition graft is placed within the aneurysm. The proximal and distal anastomoses are usually easier to perform as end-to-end anastomoses, if the native arteries are divided. This is particularly true if there is a size mismatch between the graft and the native arteries. Remember to check the aneurysm sac after that the blood flow has been restored, since back bleeding may occur from branches that were silent during clamping. The remaining part of the aneurysm sac is used to cover the graft. After the completed procedure, fascia and skin are closed with interrupted stitches. Since the popliteal fossa is a confined space without possibility of expansion, most experts recommend active drainage to remove any blood for 1-3 days after surgery. Steps of this procedure are shown in the Figure 3.

Figure 3. A lazy S shape incision (A) is placed in a popliteal fossa with proximal part located medialy and distal part laterally. The subcutaneous tissue is divided and the artery located (B) The tibial nerve is carefully held laterally(C). Popliteal aneurysm is replaced with a dacron graft (due to a large artery) (D) and is covered with part of the aneurysm sac (E). Finally subcutaneous tissue is sutured with continuous sutures and the same procedure for the skin (F) (with courtesy of Dr D Högberg, Sahlgrenska University Hospital, Gothenburg).

Figure 4. A posterior approach with a short interposition vein-graft.

Medial approach

The patient is placed supine, with the hip abducted 30°and knee flexed 45°, and a pillow placed under the knee¹Rich NM. Popliteal entrapment and the posterior approach to the popliteal artery. In. Greenhalgh RM (ed). Vascular and endovascular surgical techniques 3rd Edition 1994, WB Saunders Company, Philadelphia, London, Sydney, Toronto pp330-4.,²Lazar B. Davidovic. Surgery of the popliteal artery. 2014 – Edizioni Minerva medica s.p.a. ISBN: 978-88-7711-798-4. The presence of a PAA can change anatomical relations and make dissection more difficult. A healthy proximal section of the popliteal artery should be identified to enable proximal control, either via an incision between the Sartorius muscle above, and the semimebranosus and semitendinosus muscles below, or in case of more extensive aneurysm morphology a separate proximal incision to expose the SFA or even common femoral artery. The popliteal vein, or rarely the nerve can be very close to the PAA and care should be taken to prevent injury of these structures.

For approach to distal popliteal artery, a longitudinal “hockey stick” incision starts at the level of the medial femoral condyle and follows posteromedial edge of the tibia and might be used for GSV harvesting as well. Once the GSV is harvested, the fascia just behind the tibia is opened and extended proximally with the resection of the pes anserinus, exposing the medial head of the gastrocnemius and the tibial nerve, the popliteal artery and vein, separating them after careful ligation of their small branches.

The distal extension of the incision depends on planned location of distal anastomosis. It is important to provide sufficient space for popliteal artery clamping, and its ligation above and below the aneurysm sac, or aneurysm resection (at least partial), if planned, as well as the proximal and distal anastomoses. Tunneling, is the next phase, done by blunt digital dissection from above and below using both index fingers with rotational movement. Bypass can be tunnelled anatomically taking care that goes medially from medial head of the gastrocnemius muscle or subcutaneously in the position of the GSV. The configuration of the anastomosis depends on diameter of both artery and GSV as well as the location. End to side is preferable when diameters are not compatible, while kinking can be avoided with end to end anastomosis in a more proximal section of the popliteal artery.

The choice of approach is subjective, depending on how proximal the surgeon feels confident to reach from behind. For this reason, comparative studies are difficult to design. In the recent literature, there are few comprehensive reports, and the operative approach is not always described. Where included, the posterior approach is used less frequently, in around one third of the patients. This corresponds with the most recent publication from VASCUNET registry³Grip O, Mani K, Altreuther M, et al. Contemporary Treatment of Popliteal Artery Aneurysms in 14 Countries: A Vascunet Report. Eur J Vasc Endovasc Surg 2020; 60: 721-729.. Relative indications for posterior approach are compression symptoms, short aneurysms and the availability of only a short vein segment⁴Stone PA, Jagannath P, Thompson SN, Campbell JE, Mousa AY, Knackstedt K, et al. Evolving treatment of popliteal artery aneurysms. J Vasc Surg. 2013;57:1306-10,⁵Zaraca F, Ponzoni A, Stringari C, Ebner JA, Giovannetti R, Ebner H. The posterior approach in the treatment of popliteal artery aneurysm: feasibility and analysis of outcome. Ann Vasc Surg. 2010;24:863-70,⁶Beseth BD, Moore WS. The posterior approach for repair of popliteal artery aneurysms. J Vasc Surg. 2006;43:940-4;,⁷Carpenter JP, Barker CF, Roberts B, Berkowitz HD, Lusk EJ, Perloff LJ. Popliteal artery aneurysms: current management and outcome. J Vasc Surg. 1994 ;19:65-72,⁸Davidovic LB, Lotina SI, Kostic DM, Cinara IS, Cvetkovic SD, Markovic DM, et al. Popliteal artery aneurysms. World J Surg 1998;22:812-7.

When it comes to comparing early and long term results with the different techniques it is difficult to avoid bias. Patients with proximal extension of the disease above the adductor hiatus or those with distal thrombosis or embolization are not suitable for both modalities. Kroppman et al performed a case controlled study with 33 patients in each group⁹Kropman, R. H., H. C. Van Santvoort, J. Teijink, H. D. Van de Pavoordt, H. J. Belgers, F. L. Moll et al. The medial versus the posterior approach in the repair of popliteal artery aneurysms: a multicenter case-matched study. J Vasc Surg 2007;46(1): 24-30. Primary patency was better after a posterior approach, while assisted primary patency was better in the medial approach group; there was no difference in secondary patency. Meta-analysis comparing only those treatable through both surgical approaches showed better primary and secondary patency, aneurysm exclusion, and less need for reoperation in those operated via the posterior approach¹⁰Phair A, Hajibandeh S, Hajibandeh S, Kelleher D, Ibrahim R, Antoniou GA. Meta-analysis of posterior versus medial approach for popliteal artery aneurysm repair. J Vasc Surg. 2016;64:1141-1150.. In papers reporting on selection of conduit and approach, a vein graft was used more frequently, including the SSV¹¹Wengerter KR, Veith FJ, Gupta SK, Ascer E, Rivers SP. Influence of vein size (diameter) on infrapopliteal reversed vein graft patency. J Vasc Surg. 1990;11:525-31..

Late rupture

In the medial approach, instead of opening the aneurysm and ligating branches with backbleeding, healthy sections of artery above and below are ligated, in the hope the PAA will thrombose so the sac remains depressurized. Subsequent bypass reconstruction provides limb perfusion. Such a strategy carries the risk of late expansion/rupture due to collateral perfusion of the aneurysm sac, similar to a type II endoleak after EVAR¹²Adamson M, Magee TR, Galland RB. Outcome following bypass, and proximal and distal ligation ofpopliteal Br J Surg. 2007;94:179-82,¹³Mehta M, Champagne B, Darling RC 3rd, Roddy SP, Kreienberg PB, Ozsvath KJ, et al. Outcome ofpopliteal artery aneurysms after exclusion and bypass: significance of residual patent branches mimicking type II endoleaks.J Vasc Surg. 2004;40:886-900.,¹⁴Ravn H, Wanhainen A, Björck M. Risk of new aneurysms after surgery for popliteal artery aneurysm. Br J Surg 2008; 95: 571-575. The rate of late expansion/rupture may reach 10%. Most frequently, sac enlargement causes compressive symptoms. These results suggest that surveillance may be necessary after the medial approach, and reintervention of the sac becomes repressurized. Reoperation for this indication often uses the posterior approach to open the aneurysm and ligate the collaterals, without interfering with a patent bypass.

In situ or reversed bypass

Selection of different strategies does not vary from bypasses used for other indications such as CLI. In situ bypass might be indicated for longer reconstruction, when distal runoff is poor and the target artery of small caliber. In PAA of larger diameter, leaving the vein graft in anatomical position close to the aneurysm should be avoided.

Background and clinical presentation

Only 2-5% of operations on PAA are for rupture in larger series¹Ravn, H., D. Bergqvist and M. Bjorck. Nationwide study of the outcome of popliteal artery aneurysms treated surgically. Br J Surg 2007:94; 970-977.,²Sie RB, Dawson I, van Baalen JM, Schultze Kool LJ, van Bockel JH. Ruptured popliteal artery aneurysm. An insidious complication. Eur J Vasc Endovasc Surg 1997: 432-438.,³Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758.. Most publications are case reports and small series⁴Dawson I, Sie R, van Baalen JM, van Bockel JH. Asymptomatic popliteal aneurysm: elective operation versus conservative follow-up. Br J Surg. 1994;81:1504-7. with the exception of a larger, population based cohort of 45 legs⁵Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758.. Both the case-reports and the cohort underline that this is a rare event, and is easily misdiagnosed, often due to a misleading clinical picture.

In other aneurysm disease, rupture will lead to massive bleeding and an unstable patient. The PAA usually ruptures into the popliteal space, confined by muscles and tendons and the main symptoms are pain and swelling. These patients first preliminary diagnosis is often DVT or a Baker´s cyst⁶Sie RB, Dawson I, van Baalen JM, Schultze Kool LJ, van Bockel JH. Ruptured popliteal artery aneurysm. An insidious complication. Eur J Vasc Endovasc Surg 1997: 432-438.,⁷Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758.,⁸Illig KA, Eagleton MJ, Shortell CK, Ouriel K, DeWeese JA, Green RM. Ruptured popliteal artery aneurysm. J Vasc Surg. 1998;27:783-7.. In rPAA, however, the swelling can occupy the whole leg. Pressure from a large PAA or haematoma, can also cause neurological pain⁹Sie RB, Dawson I, van Baalen JM, Schultze Kool LJ, van Bockel JH. Ruptured popliteal artery aneurysm. An insidious complication. Eur J Vasc Endovasc Surg 1997: 432-438.,¹⁰Logigian EL, Berger AR, Shahani BT. Injury to the tibial and peroneal nerves due to hemorrhage in the popliteal fossa. Two case reports. J Bone Joint Surg Am. 1989;71:768-70., adding further complexity to the challenge of making a correct diagnosis. Furthermore, there is often patient delay. Diagnosis and surgical approach are presented in Figures 5 and 6.

Patients with rPAA are almost ten years older than those treated for non-ruptured PAA and the diameter is almost twice as large (median 53 mm, mean 64 mm)¹¹Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758.. In this study an unexpected finding was that almost half of the patients were on an anticoagulant at the time of rupture. This may be one explanation why the aneurysms were so large, without developing thrombosis or embolization. In a few cases, it has been reported that a PAA became infected, resulting in rapid expansion and rupture.

Treatment

Traditional treatment is open repair with a medial bypass, but the posterior approach can have advantages, depending on anatomy. ER has also been described in case reports. As the patient in most cases is haemodynamically stable, there is time to evaluate which method is most appropriate according to the symptoms, anatomy and morphology. Evacuation of the haematoma needs to be considered, as well as the potential need for fasciotomy. If a mycotic aneurysm is suspected, a vein graft should be used. In some challenging cases, the patient has acute limb threatening ischaemia, in addition to the rupture, and timing becomes critical. In these cases a temporary shunt could be considered.

Outcome

The immediate outcome after surgery was quite good (patency 90%) in the population-based cohort, but with a higher risk of amputation in patients with critical limb threatening ischaemia¹²Ravn, H., D. Bergqvist and M. Bjorck. Nationwide study of the outcome of popliteal artery aneurysms treated surgically. Br J Surg 2007:94; 970-977.. Even at one year there were few occlusions, but a high risk of death (42%) in these often old and comorbid patients¹³Ravn, H., D. Bergqvist and M. Bjorck. Nationwide study of the outcome of popliteal artery aneurysms treated surgically. Br J Surg 2007:94; 970-977.. In some reported cases, there was also rupture/dissection of the thoracic aorta, suggesting that CT angiography should be considered before surgery.

Figure 5. CT images of a ruptured PAA from different perspectives

Figure 6. A, lateral circumference                           B. Medial circumference

Ruptured popliteal artery aneurysm in the right leg. Note the bluish discoloration on top of the bulge just above the hollow of the knee (A). The dotted line delineates the (A) lateral and (B) medial circumference of hematoma in the muscle. (Courtesy of S. Acosta, Vascular Centre Malmö, Sweden and S. Mathiesen, Hamar Hospital, Hamar, Norway.) Reproduced after permission from the Br J Surg¹⁴Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758..

Patients with ALI caused by PAA present with various symptoms and signs as shown in Table 4, and the diagnosis is frequently delayed¹Jungi S, Kuemmerli C, Kissling P, Weiss S, Becker D, Schmidli J et al.Limb Salvage by Open Surgical Revascularisation in Acute Ischaemia due to Thrombosed Popliteal Artery Aneurysm. Eur J Vasc Endovasc Surg. 2019;57:393-398.,²Gabrielli R, Rosati MS, Carra A, Vitale S, Siani A. Outcome after preoperative or intraoperative use of intra-arterial urokinase thrombolysis for acute popliteal artery thrombosis and leg ischemia. Thorac Cardiovasc Surg. 2015;63:164-7.. The grade of ALI and is the main factor when choosing the treatment strategy. Patients with Rutherford grade I and IIa acute ischaemia can tolerate a delay, but those with grade Rutherford IIb ALI (any neurological impairment, sensory or motor deficiency) require immediate revascularization. Rutherford grade III limb ischaemia presents with muscle paralysis extending above the foot, profound sensory loss and inaudible arterial and venous Doppler signals³Kropman RH, Schrijver AM, Kelder JC, Moll FL, de Vries JP. Clinical outcome of acute leg ischaemia due to thrombosed popliteal artery aneurysm: systematic review of 895 cases. Eur J Vasc Endovasc Surg. 2010;39:452-7.. These patients do not benefit from attempted reconstruction and require urgent amputation, usually above the knee. Even in experienced hands open PAA repair for ALI is a demanding and prolonged operation. Leg revascularization comes at the end of the procedure. Preoperative thrombolytic therapy might improve patency of the run-off vessels not only trunks, main vessels, but also collaterals, however, it is often time consuming and the delay is not acceptable for limbs with severe ischaemia. The combination of mechanical thrombectomy and thrombolysis (performed by infusing thrombolytic drugs into the run off during the procedure), open or endovascular, as well as temporary shunting, are strategies that overcomes the downsides of both techniques and save time in patients with severe ischaemia⁴Jungi S, Kuemmerli C, Kissling P, Weiss S, Becker D, Schmidli J et al.Limb Salvage by Open Surgical Revascularisation in Acute Ischaemia due to Thrombosed Popliteal Artery Aneurysm. Eur J Vasc Endovasc Surg. 2019;57:393-398.,⁵Dragas M, Zlatanovic P, Koncar I, Ilic N, Radmili O, Savic N et al.. Effect of Intra-operative Intra-arterial Thrombolysis on Long Term Clinical Outcomes in Patients with Acute Popliteal Artery Aneurysm Thrombosis. Eur J Vasc Endovasc Surg. 2020;59:255-264..

It is difficult to compare the results of open repair with or without preoperative thrombolysis in an observational study, due to multiple confounders, and the difficulty of assessing the level of ischaemia in a retrospective analysis. In one study there was no difference in early amputation rate, however, long term results improved among those who underwent preoperative thrombolysis⁶Gabrielli R, Rosati MS, Carra A, Vitale S, Siani A. Outcome after preoperative or intraoperative use of intra-arterial urokinase thrombolysis for acute popliteal artery thrombosis and leg ischemia. Thorac Cardiovasc Surg. 2015;63:164-7.. Comparison of pre- and intraoperative thrombolysis, in patients with grade I and IIa ALI, showed a lower amputation rate and better long term patency in patients who underwent intraoperative thrombolysis⁷Claridge M, Hobbs S, Quick C, Adam D, Bradbury A, Wilmink T. Screening for popliteal aneurysms should not be a routine part of a community-based aneurysm screening program. Vasc Health Risk Manag. 2006;2:189-91.,⁸Morris-Stiff G, Haynes M, Ogunbiyi S, Townsend E, Shetty S, Winter RK, et al. Is assessment of popliteal artery diameter in patients undergoing screening for abdominal aortic aneurysms a worthwhile procedure. Eur J Vasc Endovasc Surg. 2005;30:71-4..

If the distal run-off has not been improved, due to lack of time or efficacy of preoperative thrombolysis, open repair starts with exploration of distal healthy (non-aneurysmal) vessels, when arteriotomy is performed followed by embolectomy and/or through transverse arteriotomies at the ankle level. Intraoperative angiography might facilitate selection of target vessels and thrombectomy. Infusion of Heparin into the patent distal vessels is worthwhile, whilst the bypass is constructed. If the crural vessels remain blocked, instead of Heparin, infusion of a thrombolytic drug should be considered⁹Jungi S, Kuemmerli C, Kissling P, Weiss S, Becker D, Schmidli J et al.Limb Salvage by Open Surgical Revascularisation in Acute Ischaemia due to Thrombosed Popliteal Artery Aneurysm. Eur J Vasc Endovasc Surg. 2019;57:393-398.,¹⁰Gabrielli R, Rosati MS, Carra A, Vitale S, Siani A. Outcome after preoperative or intraoperative use of intra-arterial urokinase thrombolysis for acute popliteal artery thrombosis and leg ischemia. Thorac Cardiovasc Surg. 2015;63:164-7.. As an example, 2 mg of rtPA can be administered into each crural vessel, while the bypass is made.

There are several outstanding issues regarding PAA.

• What is a meaningful definition of a PAA indicating future surveillance?

The definition of a popliteal aneurysm is controversial, and a number of definitions were suggested in different reports¹Trickett JP, Scott RAP and Tilney HS. Screening and management of asymptomatic popliteal aneurysms. Journal of Medical Screening 2002; 9: 92-93.,²Diwan A, Sarkar R, Stanley JC, et al. Incidence of femoral and popliteal artery aneurysms in patients with abdominal aortic aneurysms. J Vasc Surg 2000; 31: 863-869.,³Claridge M, Hobbs S, Quick C, Adam D, Bradbury A, Wilmink T. Screening for popliteal aneurysms should not be a routine part of a community-based aneurysm screening program. Vasc Health Risk Manag. 2006;2:189-91.,⁴Morris-Stiff G, Haynes M, Ogunbiyi S, Townsend E, Shetty S, Winter RK, et al. Is assessment of popliteal artery diameter in patients undergoing screening for abdominal aortic aneurysms a worthwhile procedure. Eur J Vasc Endovasc Surg. 2005;30:71-4.: 50% larger than a normal diameter⁵Tuveson V, Lofdahl HE and Hultgren R. Patients with abdominal aortic aneurysm have a high prevalence of popliteal artery aneurysms. Vasc Med 2016; 21: 369-375., >15 or >19 mm in diameter⁶Trickett JP, Scott RAP and Tilney HS. Screening and management of asymptomatic popliteal aneurysms. Journal of Medical Screening 2002; 9: 92-93.,⁷Diwan A, Sarkar R, Stanley JC, et al. Incidence of femoral and popliteal artery aneurysms in patients with abdominal aortic aneurysms. J Vasc Surg 2000; 31: 863-869., 50% larger than the adjacent vessel (i.e. the distal SFA) or 50% larger than the contralateral, non-aneurysmal artery⁸Trickett JP, Scott RAP and Tilney HS. Screening and management of asymptomatic popliteal aneurysms. Journal of Medical Screening 2002; 9: 92-93.. It is unknown how the risk for complications of the PAA is associated to these different definitions⁹Chan O, Thomas ML. The incidence of popliteal aneurysms in patients with arteriomegaly. Clin Radiol. 1990;41:185-9,¹⁰Varga ZA, Locke-Edmunds JC, Baird RN. A multicenter study of popliteal aneurysms. Joint Vascular Research Group. J Vasc Surg. 1994;20:171-7.. Is the risk for occlusion or embolization an effect of a relative increase in vessel size (bulging), or are larger vessels with larger aneurysms at higher risk?

• What is the indication for repair in asymptomatic PAA?

Most centres offer intervention for PAA with a diameter of 2 cm or more, with or without thrombus. The diameter is probably more associated with the risk of rupture¹¹Cervin A, Ravn H and Bjorck M. Ruptured popliteal artery aneurysm. Br J Surg 2018: 1753-1758.; how it correlates to the risk of thrombosis or embolism is less certain. The heterogeneity in results in different subgroups depending on symptoms¹²Cervin A, Acosta S, Hultgren R, Grip O, Bjorck M, Falkenberg M. Results After Open and Endovascular Repair of Popliteal Aneurysm: A Matched Comparison Within a Population Based Cohort. Eur J Vasc Endovasc Surg. 2021;61:988-97 raises the question what other factors may contribute to the risk of thrombosis/embolization? Flexion of the knee, sedentary lifestyle, small vessel size, elongation, and tortuosity could have independent or synergistic effects. A better understanding of these factors, and how they alter the haemodynamics, would enable a more accurate decision making.

• Which patients with PAAs are eligible for treatment by ER?

Minimally invasive treatment would be preferable, if the results were predictable and equivalent to open surgery (and cost effective). This is not yet the case. Even the frail patient will not benefit from ER if it is complicated by early or late stent graft occlusion. Some risk factors for adverse events and occlusion after ER have been suggested. The technical aspects of ER will undoubtedly improve with time and experience. Future prospective studies are needed to further evaluate in what cases ER can be regarded as the procedure of choice.