Interventional Strategies for Atherosclerotic Popliteal Disease
A review of the limitations and therapeutic options available for treating this challenging segment.
The popliteal segment is a frequent location of atherosclerosis stenosis and occlusion, as well as the site of unique vascular occlusive entities, such as adventitial cystic disease, popliteal entrapment syndrome, and aneurysms occurring in association with arteria magna syndrome. A nonobstructed popliteal artery is a critical determinant of long-term patency after femoropopliteal bypass surgery and is critical if synthetic bypass conduits are utilized.1
Endovascular strategies for atherosclerotic popliteal lesions have unique limitations due to distinct anatomic features. The popliteal artery extends from the adductor hiatus in the adductor magnus muscle to the origin of the anterior tibial artery and has a tapering diameter from its above-knee to below-knee segment.2
Consequently, noncompliant balloons, as well as uniform diameter stents, may therefore be oversized in the more distal treatment zone, risking arterial damage or a propensity to restenosis. Similarly, the use of undersized stents, fitted to accommodate the distal portion of a lesion, may not have adequate wall apposition at their upper margin, again increasing the likelihood of restenosis.3 Wire purchase across distal popliteal lesions has the potential to injure the crural runoff, requiring careful attention to wire positioning during interventions.
The popliteal artery is also subject to dynamic biomechanical forces during normal activities. Limited cadaver studies have shown shortening of the popliteal artery of 9% to 14%, comparable to the adductor canal region of the superficial femoral artery.4 Stents placed within the popliteal artery have the potential for marked compression, particularly with longer, more flexible stents. Although the long-term implications of this phenomenon specific to popliteal stents are not yet established, there is clearly a risk for restenosis due to axial or bending stent fatigue and subsequent fractures or overt kinking resulting in catastrophic stent failure. In addition, for patients with isolated popliteal stents, the resulting compliance mismatch between the upper edge of the stent and the adjacent bare artery results in a propensity to native arterial kinking during physiologic stresses.4
APPROACH TO ENDOVASCULAR TREATMENT
Despite the singular anatomic and biologic properties of the popliteal artery and evidence of a higher rate of failure after revascularization when compared with the superficial femoral artery,5 there is little published information differentiating popliteal artery outcomes after endovascular interventions.6 In fact, most series generally publish the results of intervention in the femoropopliteal artery as a whole, making it impossible to distinguish strategies or results of popliteal disease management per se. As a result, no guidelines can be established, and a personalized approach is necessary to match available devices and expertise to each treated individual's patterns of stenosis or occlusion.
Conventional or plain old balloon angioplasty should remain the mainstay of therapy for patients with isolated short-segment popliteal lesions that can be successfully and atraumatically traversed with a guidewire (Figure 1). The interventional wire should be maintained in view whenever possible to avoid movement into the smaller tibial arteries. Alternatively, in patients with critical limb ischemia undergoing concomitant popliteal and infrapopliteal interventions, a low-profile wire may be maintained with its tip distal to the target crural stenosis. The goal is to avoid blind trauma to the tibial arteries. Balloons should be sized to the diameter of the artery at the distal margin of the popliteal lesion; if necessary, repeat larger-size balloon inflations can be performed in the cephalad aspect of the diseased segment for the treatment of any residual narrowing.
Cryoplasty (PolarCath, Boston Scientific Corporation, Natick, MA) also represents a reasonable treatment option for stenoses or short occlusions located at flexion points, including the midpopliteal artery. Distal embolic protection has been promoted by some operators in patients with compromised tibial runoff (Figure 2), particularly to prevent conversion of claudication patients to a scenario of acute ischemia and limb salvage.
Nitinol stents remain a viable option for popliteal stenoses with residual narrowing or flow-limiting dissection after angioplasty and should be positioned so that the entirety of the diseased arterial segment is covered (Figure 2). Lateral flexion arteriography may provide additional benefit to evaluate for stent kinking, as well as acute flow-limiting angulation of the artery above and below the stent margins. In these cases, additional stent placement should be considered. Long-segment disease is probably also best treated with primary stenting, although this has not been specifically shown in the popliteal segment. Stents may also be used to "tack up" eccentric stenoses caused by friable atheroma or even in cases of focal embolic involvement of the popliteal artery to trap the thrombus and allow rapid restoration of flow (Figure 3).
The intermediate and long-term results of extirpative (eg, SilverHawk, ev3 Inc., Plymouth, MN) or ablative (eg, Turbo Elite, Spectranetics Corporation) atherectomy have not been defined in the popliteal artery. However, there is good rationale for the use of atherectomy as a debulking tool if it can facilitate successful angioplasty. Atherectomy using the SilverHawk device is also particularly useful for highly eccentric stenoses that may not respond to angioplasty alone. Another uniquely beneficial role of atherectomy is for the treatment of recurrent lesions after previous endovascular treatment. These fibrous intimal hyperplastic lesions can often be successfully treated with multidirectional atherectomy alone or as an adjunct to subsequent angioplasty or stenting (Figure 4).
Subintimal recanalization of the popliteal artery can be achieved with a high success rate when needed, particularly with the judicious use of currently available reentry devices (Pioneer Catheter, Medtronic; Outback Catheter, Cordis Corporation, Warren, NJ). Generally, subintimal recanalization should be reserved for cases of limb salvage due to lower patency rates than standard revascularization techniques. In patients with lesions that cannot be traversed in an antegrade fashion, retrograde recanalization via a popliteal (Figure 5) or even a pedal approach is possible. After retrograde traversal, the intervention can either be completed from the original arterial access site, or the patient can be placed supine, and the crossing wire snare retrieved via a contralateral (over the bifurcation) or ipsilateral (antegrade) femoral puncture, allowing completion of the case from the femoral approach. If stent placement is anticipated, this latter approach has the advantage of avoiding the placement of large sheaths in the popliteal artery, with the risk of arterial injury or difficulty with subsequent hemostasis.
Published Results of Popliteal Stenting
As noted earlier, the results of interventions in the popliteal artery have not been routinely singled out in series describing femoropopliteal treatment. Onohara et al described the results of popliteal angioplasty adjunctive to femoral to above-knee bypass grafting in 27 patients.7 One-year primary patency rates of 69% and secondary patency rates of 82% were achieved, and the results of bypass grafts performed with concomitant popliteal angioplasty exceeded that achieved with a matched group of patients undergoing femoral to below-knee bypass. Five-year primary patency was noted in 51% of patients. In a more contemporary series of 50 patients with patent femoral arteries undergoing popliteal angioplasty, Raouf and colleagues reported a comparable 2-year primary patency rate of 57%.8 Patency was better for claudicants compared with limb salvage (P=.006), focal versus long segment disease (P=.01), and in the upper versus lower popliteal artery (P=.03). There was no difference between stenoses and occlusions. These results are similar to previous pooled 1-year primary patency data of 67% for percutaneous transluminal angioplasty of combined femoropopliteal lesions.9
There are equally limited publications specifying popliteal stent outcomes. A series of Strecker stent implantations (Boston Scientific Corporation) in 32 popliteal arteries with residual post-percutaneous transluminal angioplasty stenoses reported 1- and 2-year primary patency rates of 81% and 74%, respectively.10 Equivalent patency was described for stents in the upper (P1 segment) and middle (P2 segment) third of the popliteal artery, although there was a trend for reduced results when treating occlusions and in patients with impaired runoff. The use of 4-F sheath-compatible self-expanding popliteal and tibioperoneal stents has been recently reported in 35 patients with severe claudication and critical limb ischemia.11 A total of 33 stents were placed in the distal popliteal artery (P3 segment) with a combined 6-month primary cumulative patency rate of 82% and a 1-year rate of approximately 50%. Stent fractures were not described in either of these series.
The popliteal artery segment presents challenging problems to the endovascular interventionist due to its distinct anatomy, the various disease entities affecting it, its importance in bypass surgeries, and the unique dynamic forces it is subjected to during normal activity. These same factors can have an adverse impact on the long-term success of endovascular interventions on this arterial segment.
Although conventional balloon angioplasty remains the optimal therapy for de novo short-segment popliteal lesions, there are many other therapeutic options available to the interventionist for lesions with more complex anatomical and clinical characteristics. These include cryoplasty, primary or secondary stenting, atherectomy, and the use of reentry devices. Endovascular techniques, such as retrograde catheterization of the popliteal artery, can be helpful in the difficult-to-cross popliteal lesions. The use of these therapeutic options and their success will ultimately depend on their appropriate application and the experience of the operator. These devices and techniques should always be employed with careful consideration of the delicate distal crural arteries. Distal embolic protection and the careful positioning of guidewires can be helpful in this regard.
Many inferences on the best treatment for complex popliteal lesions are best drawn from the experience in the trials on the endovascular treatment of the diseased femoropopliteal segment and those of the operator. Ultimately, there is a need for high-quality randomized clinical trials that specifically target the diseased popliteal artery segment and the appropriate application of the techniques and devices we have described.
John H. Rundback, MD, is Director, Interventional Institute, Holy Name Hospital, and Associate Professor of Radiology, Columbia University College of Physicians and Surgeons, Teaneck, New Jersey. He has disclosed that he is a paid consultant to ev3 and Medtronic. Dr. Rundback may be reached at firstname.lastname@example.org.
Luis Rodriguez, Jr, MD, is from the Interventional Institute, Holy Name Hospital, in Teaneck, New Jersey. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Rodriguez may be reached at (201) 833-3310; email@example.com.