Infrapopliteal Bypass

Infrapopliteal bypass is a major lower-extremity arterial reconstruction, the goal of which is to establish inline flow to target vessels such as the tibial, peroneal, or pedal arteries. Arterial supply (inflow) sites therefore include the common femoral, deep femoral (profunda femoris), superficial femoral, and popliteal arteries. Occasionally, a tibial artery may become the inflow vessel.

The primary indication for infrapopliteal bypass is critical limb ischemia (CLI) due to atherosclerotic peripheral arterial disease (PAD). This method of surgical arterial reconstruction can be applied to patients with nonatherosclerotic conditions such as aneurysmal disease and traumatic arterial injuries. The bypass conduit should usually be composed of autogenous vein, but prosthetic material can be used in the absence of suitable autogenous conduit.[1]

With regard to conduit type, vein grafts are superior to all prosthetic conduits for infrapopliteal bypass, regardless of target vessel.[2, 3, 4] The great saphenous vein (GSV; also referred to as the long or greater saphenous vein) is the most commonly utilized autogenous conduit; however, the small saphenous vein (SSV; also referred to as the short or lesser saphenous vein), the superficial femoral vein,[5] and spliced vein grafts from the arm can also be used.[6, 7]

Numerous varieties of prosthetic conduits are available; options include the following:

• Dacron
• Heparin-bonded Dacron
• Human umbilical vein
• Polytetrafluoroethylene (PTFE)
• Heparin-bonded PTFE

Of these, PTFE is the most commonly used material. All prosthetic grafts perform with similar patency rates in the infrapopliteal position and are inferior to autogenous grafts, regardless of type; composite grafts appear to be no better than prosthetic grafts in this regard.[3] The 1-year patency rates of vein conduit in the infrapopliteal position reach 70-80%, whereas those of prosthetic grafts reach 30-50% at best.[2] If a prosthetic graft is used in the infrapopliteal position, an adjunctive vein cuff at the distal anastomosis improves patency.[8]

Indications for infrapopliteal bypass include the following:

• Symptomatic lower-extremity ischemia (eg, disabling claudication, rest pain, or tissue loss)
• Aneurysmal disease
• Traumatic arterial injury

In 2019, the Global Vascular Guidelines were published via a joint effort from the the European Society for Vascular Surgery (ESVS), the Society for Vascular Surgery (SVS), and the World Federation of Vascular Societies (WFVS).[9]  The GVG program endorsed the SVS Threatened Limb Classification system, based on grading of Wounds, Ischemia, and foot Infection (WIfI). It also proposed the Global Anatomic Staging System (GLASS), which involved defining a preferred target artery path and then estimating limb-based patency, from which three stages of complexity for intervention were derived.

Contraindications for infrapopliteal bypass include the following:

• Debilitated patient with severe comorbidities
• Lack of an appropriate distal target for revascularization
• Unaddressed inflow disease
• Severe joint contractures
• Nonambulatory patient

Best practices

The principles of surgical revascularization are based on the following three components:

• Inflow
• Outflow
• Conduit

The inflow vessel (ie, the artery from which the bypass will originate) must have adequate flow and pressure and allow suturing. Significant vascular calcification or atherosclerotic disease of the inflow artery can present technical challenges. The outflow vessel should be the least diseased vessel with runoff to the foot. On imaging, inflow and outflow arteries must be well characterized. If disease exists in the proposed inflow vessel and a less diseased more proximal artery cannot be accessed or used because of bypass graft length constraints, an adjunctive procedure to address the inflow disease (eg, endarterectomy) must be added to the operative plan.

The distal target artery must be confirmed to be the dominant vessel to the foot. Tissue distribution of the outflow vessels must correlate with the operative indication. For example, whereas revascularization of the pedal arteries will aid in healing of ischemic foot ulcers, it will not improve calf claudication. In general, shorter reconstructions, if feasible, have better long-term patency.[2, 10]

With regard to conduit assessment, duplex vein mapping is vital for ensuring a graft of appropriate size and quality. The venous conduit should be at least 2.5 mm in diameter and soft throughout the length needed to perform the bypass. Calcified or sclerotic veins should not be used.

Complication prevention

Measures to help prevent complications include the following:

• Thorough preoperative assessment of the inflow and target vessels
• Thorough assessment of the vein conduit
• Strict attention to sterile technique in the handling of prosthetic grafts
• Systemic heparinization of patients before vessel clamping and after graft tunelling
• Assessment of the reconstruction at the time of the operation with duplex ultrasonography (US) or intraoperative arteriography

Popplewell et al evaluated outcomes in a subgroup of 104 patients with infrapopliteal disease from the BASIL (Bypass vs Angioplasty in Severe Ischaemia of the Leg)-1 trial who were treated with infrapopliteal vein bypass (VB; n = 56) or plain balloon angioplasty (PBA; n = 48).[11]  There were no significant differences in amputation-free survival (AFS) or overall survival (OS). The VB group had significantly quicker relief of rest pain but did not show significantly improved tissue healing. Median length of index hospital admission was significantly greater in the VB group (18 vs 10 days) but median total hospital stay between randomization and the primary endpoint was not (43.5 [VB] vs 42 [PBA] days).

Subsequently, Popplewell et al published prospectively gathered data on 137 consecutive patients with CLI from infrapopliteal disease who underwent PBA or VB in their unit between 2009 and 2013.[12]  Outcomes were similar to those reported in BASIL-1. Bypass patients spent more days in hospital during the index admission (median, 9 d vs 5), but not out to 12 months (median, 15 d vs 13). They had a higher rate of 30-day morbidity (36% vs 10%), mainly due to infective complications, but not of 30-day mortality (3.1% vs 6.8%). AFS and OS were better after bypass, but limb salvage (LS) and freedom from arterial reintervention (FFR) were not.

Morisaki et al retrospectively studied treatment outcomes in 99 CLI patients (106 limbs) who underwent infrapopliteal bypass either as initial treatment (n = 75; 82 limbs) or after initial endovascular therapy (n = 24; 24 limbs).[13]  Outcome measures included graft patency, limb salvage, AFS, and OS. Primary patency at 1 and 2 years was 72.0% and 67.5% for the bypass-first group, compared with 53.1% and 47.2% for the endovascular-first group. There were no differences in secondary patency, limb salvage, AFS, or OS.

Yan et al studied in-hospital and follow-up (≥1 y) outcomes of 32 patients who underwent infrapopliteal bypass surgery for treatment of atherosclerosis (ASO; n = 14) or thromboangiitis obliterans (TAO; n = 18).[14]  In-hospital patency rates were 77.8% for TAO patients and 92.9% for ASO patients. Patency rates at follow-up were 44.5% for TAO patients and 85.7% for ASO patients. Despite the lower patency at 1 year, TAO patients experienced relief of ischemic symptoms and improvement in ABI.

Patients requiring arterial reconstruction of the lower extremities frequently have significant medical comorbidities, with a particularly high prevalence of coronary artery disease (CAD).

A thorough and expeditious perioperative assessment and optimization of underlying CAD and medical comorbidities should precede intervention. First, it is essential to confirm ischemia-related claudication and critical limb ischemia (CLI), which is defined as rest pain and tissue loss. Functional and ambulatory status should be carefully assessed; patients with limited function of the affected limb should not undergo major extremity revascularization.

Assessment of lower-extremity arterial insufficiency should begin with the ankle-brachial index (ABI) and be followed by detailed anatomic characterization of the inflow and outflow arteries.[15]

The criterion standard imaging modality for defining the vascular anatomy before revascularization is arteriography. Substantial advances have been made in computed tomography (CT) angiography (CTA) and magnetic resonance angiography (MRA), and these modalities may provide sufficient detail for operative planning. In patients with relative contraindications for these imaging modalities, duplex arterial mapping may provide the anatomic information needed to proceed without formal arteriography.

Equipment employed for infrapopliteal bypass incldues the following:

• Standard vascular clamps and instruments
• Tunneling device (eg, Gore tunneler; W. L. Gore and Associates, Flagstaff, AZ)
• Polytetrafluoroethylene (PTFE) or other prosthetic grafts of appropriate length and caliber (for infrainguinal and infrapopliteal reconstruction, 6-mm grafts are commonly used)
• Doppler ultrasonography (US) device to assess blood flow intraoperatively

Anesthesia

The operation is most often performed with general anesthesia because exposure of the groin, exploration and harvesting of vein conduits, and tunneling of the graft proximal from the groin to the distal target site can be difficult to tolerate. In cases where underlying cardiopulmonary disease precludes general anesthesia, however, the procedure can be performed with spinal or regional anesthesia and sedation.

Positioning

The procedure is performed with the patient supine. The patient is prepared in a sterile fashion from the umbilicus down to the lower extremities. The extremities are prepared circumferentially. If an upper-extremity vein is required, the arms are extended and prepared.

Establishment of graft surveillance protocols is essential to maintaining the long-term patency of lower-extremity bypass grafts. Lesions that threaten graft patency can be readily identified and monitored for progression with serial ABI determination and graft duplex US.

The authors' center uses scheduled examination at 1 month postoperatively, then at 3 months, at 6 months, and yearly thereafter. Grafts with focal lesions associated with a peak systolic velocity higher than 300 cm/s, a velocity ratio greater than 3.5, or a change in ABI greater than 0.15 undergo further imaging with arteriography or MRA to identify potential inflow, outflow, or other graft lesions, which are addressed expeditiously.

Infrapopliteal bypass involves establishing inline arterial flow to target vessels such as the tibial, peroneal, or pedal arteries, using the common femoral, deep femoral (profunda femoris), superficial femoral, or popliteal artery (or, occasionally, a tibial artery) as the inflow vessel. The video below demonstrates a bypass from the popliteal artery to the dorsalis pedis.

Exposure of vessels

Proximal femoral artery and its branches

Longitudinal or oblique groin incisions are used for the femoral exposure. The incision is carried along the femoral pulse at the level of the common femoral artery (the inguinal ligament is often used as the landmark for the proximal common femoral artery).

Subcutaneous tissues are dissected and the femoral sheath entered. The artery lies lateral to the femoral vein. The common, superficial, and deep femoral (profunda femoris) arteries are dissected and controlled with vessel loops.

Attention is paid to preserving flow to and avoiding injury to the deep femoral artery during dissection. Care must also be taken in mobilizing and identifying the lateral circumflex femoral vein to avoid injury. Circumflex branches to the femoral artery are controlled and preserved.

A more proximal dissection to the external iliac artery may be required if vascular clamps cannot be safely applied to the common femoral artery. To facilitate this exposure, the inguinal ligament may have to be divided. This is repaired at the completion of the bypass reconstruction.

A significantly diseased femoral artery may require an endarterectomy with subsequent angioplasty in order to make it suitable for bypass grafting.

Distal femoral artery and above-knee popliteal artery

The knee is flexed and a roll placed underneath the thigh. A longitudinal skin incision is made in the lower medial thigh at the intermuscular groove between the superior edge of the sartorius and the inferior edge of the vastus medialis. Care is taken in avoiding injury to the great saphenous vein (GSV), which runs close to this area.

Fascia is incised longitudinally, and the sartorius is reflected posteriorly, along with the semitendinosus and the gracilis. The adductor magnus is retracted anteriorly and the adductor canal exposed. The popliteal fat pad is exposed, and careful dissection is performed close to the femur to identify the artery and vein (see the image below).

Below-knee popliteal artery

The knee is flexed, and a roll is placed underneath the thigh. A longitudinal incision is made 1-2 cm below the posterior edge of the tibia just distal to the medial tibial condyle and extended as needed (typically 10-12 cm). Care is taken in preserving the GSV.

The fascia overlying the gastrocnemius is incised longitudinally. The plane between the soleus and the gastrocnemius is developed. The soleus is retracted anteriorly; the gastrocnemius is retracted posteriorly. (See the image below.) The below-knee popliteal space is entered, and the artery is typically seen to be surrounded by two veins. The tibial nerve is posterior to the vascular bundle. Sharp dissection is carried out to delineate the anterior tibial artery and the tibioperoneal trunk. The soleus may have to be divided to afford further exposure.

Posterior tibial and peroneal arteries

The knee is flexed and rotated laterally. A roll is placed below the calf. A longitudinal incision is made 1-2 cm below the posterior edge of the tibia in the midleg and is extended proximally or distally as needed. This incision overlies the course of the GSV; care is taken to avoid injury to the vein during this exposure. The incision is carried down to the fascia, whereupon the fascia is incised and the gastrocnemius is mobilized and retracted posteriorly.

Soleus muscle attachments to the tibial edge are divided, allowing entrance to the deep posterior compartment. The posterior tibial artery should be accessible and is generally surrounded by a pair of tibial veins. The peroneal artery lies deeper to the tibial vascular bundle within this compartment (see the image below).

Anterior tibial artery

The knee is flexed with a roll underneath the calf. A longitudinal incision is made in the skin overlying the plane between the tibialis anterior and the extensor digitorum longus, to be extended as needed. The intermuscular groove is entered. The anterior tibial artery courses along with the deep peroneal nerve just superficial to the interosseus membrane. Again, the artery is typically enveloped by a network of tibial veins (generally paired).

Pedal arteries

Pedal vessels are relatively easy to identify because they are superficial. A Doppler probe can aid in identifying the location of both the dorsalis pedis artery and the distal posterior tibial artery. A longitudinal incision is made overlying the course of the vessels for exposure.

Preparation of conduit

If a GSV is deemed suitable as a bypass conduit, the vein can be completely mobilized and then reversed; alternatively, the vein can be left nonreversed, which requires subsequent lysis of the valves. If the inflow site is in the ipsilateral groin, the vein can also be left in situ and not mobilized from its bed; this technique also requires lysis of the valves.

An adequate conduit vein is mapped and marked preoperatively. The vein is then exposed through medial incisions that overlie the course of the vein. Tributaries to the vein are carefully ligated with silk ties. The vein is then gently distended, and any leaks are addressed. The vein is placed in heparinized saline until one is ready to construct the bypass.

With the in-situ bypass, the vein is exposed and not mobilized from its bed, except at the proximal and distal ends. As the vein is exposed, tributaries are tied off with silk ties. The proximal vein is mobilized, and the first valve is excised under direct vision. Once this is done, the proximal anastomosis can be performed.

Once the proximal anastomosis is complete and flow is established to the conduit, the first competent valve impedes flow. A valvulotome is then used to perform careful lysis of the valves. Preserving select side branches to allow passage of the valvulotome is important.

Alternatively, the GSV may be harvested endoscopically, which minimizes the incision length on the leg of the patient. In this technique, the vein is harvested with the aid of an insufflation device and laparoscopic camera. Once the vein is removed from its bed, the tributaries are ligated, much as with the open method described above.[16]

Tunneling of graft

Before systemic heparinization, graft tunneling is performed. A graft tunneling device (eg, Gore Tunneler; W. L. Gore, Newark, DE) is generally used to create tunnels. Tunneling can be anatomic or subcutaneous, depending on the target vessel. The diameter of the tunneling instrument must be sufficient to create a tunnel wide enough to prevent compression of the graft. The route for tunneling to the posterior tibial artery or peroneal artery can be anatomic or subcutaneous.

The anatomic route follows the posterior edge of the sartorius, enters the popliteal fossa between the two heads of the gastrocnemius, and passes anterior to the soleus to the posterior tibial artery. This is the preferred tunneling route for reversed saphenous or prosthetic grafts. The graft is less subjected to kinking when routed anatomically. In the subcutaneous route, a tunnel is made that runs along the anterior medial surface of the thigh, then the medial side of the knee and leg. The aponeurosis of the leg should be incised enough to avoid sharp angulation of the graft as it enters the target vessel.

The route for tunneling to the anterior tibial artery can also be anatomic or subcutaneous. Subcutaneous tunneling may be technically easier and courses anterolaterally at the lower thigh and lateral side of the knee and leg. For in-situ bypasses, the lower part of the popliteal fossa is divided, and the interosseous membrane is freed and incised longitudinally to allow passage of the graft to the anterior compartment. The distal anastomosis is constructed at a point that avoids sharp angulation as the graft exits the interosseous tunnel.

Construction of bypass

The patient is heparinized systemically with 80 units/kg of heparin before the inflow vessel is occluded. The activated clotting time is maintained above 250 seconds to prevent thrombotic complications. Longitudinal arteriotomies are made on the artery and extended with angled Potts scissors. The graft is spatulated, and typically, an end-to-side anastomosis is created with 5-0 or 6-0 polypropylene suture (see the image below).

After completion of the proximal anastomosis, flow is established through the graft, and its adequacy is confirmed. Vein grafts are left distended and marked for orientation. The graft is passed carefully through the tunnel in such a way as to ensure that there are no kinks or twists.

Before construction of the distal anastomosis, the lie of the graft is carefully assessed with the leg extended. The goal is to keep the graft as parallel to the target vessel as possible; this may necessitate modifications to the tunneling and further dissection and mobilization of the surrounding muscular aponeurosis.

Once length and lie are assessed, the graft is cut to size and the end spatulated. The anastomosis is then created in an end-to-side fashion with a continuous polypropylene suture; for tibial and pedal vessels, 6-0 or 7-0 polypropylene sutures are typically used. Before the completion of the anastomosis, the artery is back-bled and the graft flushed.

Once the anastomosis is complete, the bypass is carefully examined. The authors' center typically performs completion arteriography after the construction of the distal anastomosis. Some centers perform intraoperative duplex ultrasonography (US).

Hemostasis is thoroughly ensured in the wounds. The groin wound is closed in multiple layers of polyglactin suture to obliterate potential space. The leg wounds are closed in layers with polyglactin suture for the fascial and dermal layer. Skin can be approximated with staples or nylon suture on either site.

Doppler US signals should be checked frequently, and routine bedside ankle-brachial indices (ABIs) are obtained daily to monitor graft patency if pedal pulses cannot be palpated after the reconstruction. Any question regarding graft patency should prompt the performance of duplex US or another imaging investigation.

Patients are maintained on an antiplatelet agent, a beta blocker, and a statin. A study by Gupta et al suggested that dual antiplatelet therapy (DAPT) may have an advantage over single antiplatelet therapy (SAPT) after bypass when prothetic grafts are used, but not when vein grafts are used.[17]  In a study comparing SAPT, DAPT, and anticoagulation in Medicare beneficiaries who had undergone infrapopliteal bypass for CLI, Marcaccio et al found that as compared with SAPT, DAPT and anticoagulation therapy were not associated with improved outcomes.[18]

Systemic anticoagulation is reserved for high-risk grafts (because the risk of major bleeding is significant), reoperative cases, poor arterial runoff, and distal bypasses using prosthetic or suboptimal vein graft. Perioperative antibiotics are stopped 24 hours after surgery unless active infection is present. Patients with significant edema are treated with ACE compression (avoided with in-situ or subcutaneous vein grafts) and leg elevation.

Potential complications of infrapopliteal bypass include the following:

• Lymphatic leak
• Bleeding/hematoma
• Graft thrombosis
• Graft infection

Early graft thrombosis and delayed pseudoaneurysm of the graft may be a sign of underlying graft infection.

If an initial distal bypass fails, a redo bypass may be considered; however, patency and survival appear to be significantly lower.[19]