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Arterial Surgery of the Leg
Femoral-Popliteal Bypass

Arteries in any part of the body may block (occlusive vascular disease). It is not limited to the lower extremities (legs). Arteriosclerosis (hardening and thickening of the artery wall) is most often associated with hypertension and diabetes. With the increase in the number of risk factors (age, diabetes, hypertension, obesity, elevated cholesterol and lipids) and an aging population, the incidence of occlusive vascular disease is rapidly increasing. The goal of surgery to correct occlusive vascular disease in the legs is the saving of life and limb. There are several procedures for treating occlusive vascular disease, but at the end of 5 years only 65 - 75% of procedures remain successful.

Anatomy

  • There are three types of arteries (Figure 1):
    1. Large or elastic - aorta and its large branches (e.g. iliac arteries)
    2. Medium sized or muscular (e.g. femoral and popliteal arteries)
    3. Small arteries - usually less than two millimeters and within tissues of organs
  • The walls of arteries consist of (Figure 2):
    1. Intima - lining cells along with minimal underlying tissue
    2. Internal Elastic Membrane - a dense elastic membrane that separates intima and media
    3. Media - smooth muscle cells
    4. External Elastic Membrane - an elastic membrane separating media and adventia
    5. Adventitia - outer connective tissue (fibrous) layer
  • In muscular arteries, the media is composed mostly of smooth muscle cells that regulate blood flow and pressure in the tissues. Nerves that control the size of blood vessels are not under voluntary control (the autonomic nervous system). Local tissue metabolism also contributes to vessel size (e.g. carbon dioxide build up causes the vessels to dilate)
  • Arteries serve to deliver nutrients (food) and oxygen to tissue capillaries. At rest blood flow to a normal leg averages 300 - 400 milliliters/minute (1/3 quart per minute). With moderate exercise flow increases 5 - 10 times
Figure 1 - Arteries of the leg. © J. NorahFigure 2 - Cross-section of a normal artery and an artery with plaque. © J. Norah

Pathology

  • Atherosclerosis is a form arteriosclerosis in which the artery walls are thickened with a fatty material called a plaque. Atherosclerosis is a disease mainly of large and medium sized arteries
    1. The plaques tend to form at arterial bifurcations (branch points)
    2. Low density lipoprotein (LDL) cholesterol migrates beneath the intima and forms foam cells. Groups of these cells form the first visible evidence of plaque formation, which continues to grow and become a fibrous plaque
    3. Some of these cells die. Cell debris and fatty material build up and a more complex plaque forms. Complex plaques are unstable and hemorrhage into the plaque may occur and obstruct the blood vessel
    4. Plaque enlargement may cause intimal ulceration, which attracts platelets (sticky particles in the blood) and causes blood clots within the vessels. Mature plaques will frequently also have calcium deposits.
  • Critical stenosis is the degree of narrowing at which blood pressure and flow begin to be affected, usually greater than 50% diameter reduction
  • Embolization is the passage of embolic material (usually old clot from the heart or artery wall) to any distant arterial site
    1. The common femoral artery bifurcation is the most common embolic site
    2. Tiny cholesterol emboli from ulcerated arteries may pass to the small vessels of the toes and foot (blue toe syndrome or trash foot syndrome). Embolization will almost always cause symptoms acute ischemic (lack of oxygen) symptoms
  • Aneurysms (localized enlargements involving entire arterial wall) of the lower extremity occur with the popliteal artery being the most common
    1. Aneurysms may be multiple. There is a tendency for bilateral popliteal aneurysms
    2. Popliteal aneurysms may form clots and cause loss of the limb
    3. Extremity aneurysms are not as prone to rupture as aortic aneurysms.
  • Diabetic patients have an increased rate of changes in the popliteal arteries
  • Hypertensive and diabetic patients are also prone to thickening of arterioles (smallest arteries) with loss of structure and narrowing of the lumen (inner channel of the vessel).

History

  • The classical symptoms of chronic occlusive vascular disease are intermittent claudication (pain caused by activity and relieved with rest), non healing ulceration of the foot, rubor (red color), and rest pain (pain without activity)
  • These symptoms usually start with intermittent claudicaton (pain on walking), which progresses to pain at rest. The majority of people with intermittent claudication will never require surgery
  • Acute arterial occlusion frequently presents with the five P's, sudden pain, pallor, pulselessness (loss of the pulse), paresthesias (abnormal sensations) and paralysis. All five of these symptoms may or may not be present
  • Several conditions aggravate atherosclerosis and success of a bypass graft
    1. A past history of diabetes, hypertension, elevated cholesterol or lipids or smoking
    2. Vasculitis (inflammation of blood vessels), collagen disease (e.g. lupus), hypercoagulable syndrome (increased clotting of blood), Buerger's disease (occlusive arterial disease different from atherosclerosis), previous operations on blood vessels, coronary artery disease (see Coronary Artery Bypass Graft), renal (kidney) disease, and cerebrovascular (arteries of the brain) disease is important
  • Intermittent claudication involving the calf muscles is usually the first symptom of peripheral vascular occlusive disease. The muscle blood flow is unable to meet the requirements of activity. The pain is related to the accumulation of waste products in the muscle
  • Severe ischemia (lack of blood supply) will cause pain in the toes and distal forefoot when at rest. There is also reddening of the toes when the foot hangs down
  • Long standing diabetes causes a peripheral neuropathy (disease of the nerves) in which the sensation of foot pain is diminished
  • Ischemic ulceration will frequently involve the toes and top of the forefoot

Examination

  • The legs are examined for skin color (pallor/rubor), temperature (warm/cool), hair distribution, muscle atrophy (shrinkage), mottling, edema (swelling), ulceration, discoloration, and sensation (present/absent)
  • The legs are checked for the presence or absence of pulses at the groin (femoral), behind the knee (popliteal), top of the foot (dorsalis pedis), and behind the inner ankle (posterior tibial)
  • Filling of the capillaries (smallest vessels in the tissues) is determined by compressing the skin of the toe to displace the blood under the examiner's finger. The toe blanches and the time for the capillaries to refill back to a normal color is determined. A prolonged refill time indicates a poor circulation
  • The condition of the saphenous veins in the groins, which may be used for bypass surgery, is determined

Testing

Several tests are used to evaluate the lower extremity circulation.

  • Pulse Volume Recordings (PVR's) - blood pressure cuffs are placed around the upper thigh, calf, ankle, and toes. The cuffs are inflated to 65 mm/Hg Mercury (millimeters/mercury. A waveform is obtained that reflects blood volume change during systole (during the pulse) and diastole (between the pulses) under the cuff
  • Color Flow Duplex Scanning - combination of Doppler B mode (evaluates arterial wall and plaques) and pulsed Doppler (characterizes flow disturbances and velocity of flow). Duplex scanning provides anatomic and physiologic information and is an excellent study for screening, diagnosis, and follow-up (Figure 3)
  • Magnetic Resonance Angiography (MRA) - is carried out using the MRI scanner. It gives a picture of the arteries without having to invade the body (non invasive). No dye is given.
  • Angiography - A needle or small catheter is passed into the artery and contrast material (dye that shows up on X-ray) is injected into the vessel and imaged by X-ray. (Figure 4)
  • Carbon Dioxide Angiography -carbon dioxide is directly injected into the artery with X-ray examination of the vessels
Figure 3 - Doppler ultrasound scan of the femoral artery showing an area of stenosis. Courtesy S. Sadiq, MDFigure 4 - Before. Femoral angiogram showing irregular narrowing of the femoral artery in the thigh. After. Following balloon angioplasty the artery is no longer narrowed. Courtesy S. Sadiq, MD

Nonsurgical Therapy

  • Initial treatment consists of risk factor modification
    1. Lowering blood cholesterol by diet and cholesterol lowering medication
    2. Stop smoking - this is a must
    3. Dietary modification
    4. Exercise program appears to provide significant benefit. In fact several early studies comparing surgery with exercise programs favored the exercise program for individuals with claudication
  • Drug therapy. The use of drug therapy has generally been disappointing
    1. Pentoxiflylline (Trental®) has been available for many years. It appears to have only a limited benefit for most patients
    2. Cilostazol (Pletal®), a newer medication, shows promise as an agent to improve walking distance

Surgical Procedures

There are several procedures that may be used to improve the blood supply to the legs.

  • Most operations are performed under continuous epidural or spinal anesthesia (See Anesthesia). Local or general anesthesia may be used in certain instances. Antibiotics are usually given before surgery. Anticoagulation (blood thinners) is routinely used during surgery. Sometimes tourniquets may be used to reduce bleeding during surgery
  • Embolectomy
    1. The purpose of this procedure is to remove a localized clot in an artery
    2. An incision is made in the skin over the artery and the artery exposed
    3. A small incision is made in the artery and a small balloon tipped catheter is inserted. The catheter is pushed pass the clot, the balloon inflated and the catheter removed dragging the clot with it
    4. The incision in the artery is closed with sutures
  • Endarterectomy
    1. An incision is made in the skin over the vessel that is blocked with plaque (Also see Carotid Endaterectomy)
    2. Special clamps that do not injure the artery are applied to the artery before and after the plaque
    3. An incision along the length of the artery is made in the arterial wall
    4. The plaque is peeled out of the artery and the incision closed with fine with or without a patch. The patch is made be of a section of vein or a prosthetic (artificial) material
  • Bypass graft
    1. A bypass graft channels blood around a block in an artery
    2. The ideal graft material is autogenous (patient's own) saphenous vein without disease that is 5 millimeters (1/5 inch) in diameter or greater and long enough to span the distance around the block. The lesser saphenous vein and forearm veins are alternative autogenous vein donor sites. Different synthetic materials are also available, but the vessel is more likely to remain open if autogenous material is used
      • The vein graft is obtained by making an incision over the full length of the graft. Any side branches are tied. The graft is then reversed in direction because small valves in the wall of a normal leg vein, which prevent venous back flow, will prevent blood flow into the leg when used as an arterial graft
      • Another method of preparing the vein graft that reduces the incision size is to leave the saphenous vein in place (in situ graft). The valves in the vein are removed by inserting a small scope and a cutting instrument called a valvulotome that removes the valves, and any side branches are tied off
      • The results of reversed vein grafts versus in situ grafts are similiar without a distinct advantage for either
    3. An incision is made in the skin over the length of the artery that is blocked. The artery is exposed and vascular clamps placed on the artery before and after the blocked area. Small incisions are made in the side of the artery before and after the block. The ends of the graft are then anastomosed (sutured) to the incisions in the side of the artery
    4. The patient must know that it is important to have routine follow up of the graft. Color flow Duplex scanning is the preferred method. Approximately 10-30% of bypass grafts below the groin will show stenosis (greater than 50% diameter reduction). Sixty to eighty percent of these occur within 1st year. Five to ten percent develop after 2nd year and graft failure is three fold greater if stenosis present
    5. Femoral Popliteal Bypass - the bypass graft is used to bridge a blockage between the common femoral artery and popliteal artery near the knee (Figure 5) (Animation)
    6. Femoral Infrapopliteal Bypass - a venous graft is used to bridge from the femoral artery to one of the arteries below the knee (e.g. peroneal, posterior tibial, anterior tibial, or pedal artery (Figure 6 and 7)
  •  
    Click image to view animation
    Figure 5 - Femoral popliteal bypass. Obstruction of the superficial femoral artery bypassed with a venous graft. © J. Norah
    Animation demonstrating a femoral-popliteal bypass. The femoral artery is exposed in the groin and the popliteal artery exposed above and behind the knee. The arteries are clamped with vascular clamps. A saphenous vein graft is passed along side the femoral artery. Sometimes the graft is composed of a prosthetic material. The graft is then sutured into an opening in the side of the femoral artery and then into the side of the popliteal artery. The clamps are removed to allow flow of blood around the blocked portion of the artery.
Figure 6 - Femoral infrapopliteal bypass. Obstruction of the popliteal artery at the knee bypassed with a venous graft. © J. Norah Figure 7 - Angiogram obtained after a femoral popliteal bypass using a venous graft. Courtesy S. Sadiq, MD
  • Interposition Graft - This involves the replacement of a short segment of blocked artery or aneurysm (dilated artery) with a graft. After the vascular clamps are applied, the artery segment is removed and the ends of the graft are sutured to the ends of the cut arteries (end to end anastomosis)
  • Angioplasty of lower extremity vessels is a common endovascular procedure with or without stent placement (Figure 8). An endovascular procedure is one in which the procedure is carried out from within the blood vessel
    1. Under X-ray control, a catheter with a special balloon is placed into the area of an artery narrowed by a plaque
    2. The balloon is positioned in the plaque and the balloon expanded causing the plaque to be compressed against the artery wall. The ideal angioplasty is performed on a single short segment of artery
    3. A stent may be placed to help keep the artery open. A stent is a metal (usually titanium) mesh. After the balloon is expanded, a second catheter with a collapsed stent over a balloon is placed. The balloon is dilated causing the stent to expand and hold the artery open.
    4. Most lower extremity vessels will have multiple stenoses, which makes long term patency (opening) difficult to achieve with multiple dilatations with or without stents
    5. Stent placement below the knee in single vessels is being done with mixed results. Newer approaches to maintain patency include local radiation of plaque site or stents impregnated with certain drugs
  • The effectiveness of a given procedure can be evaluated at the time of surgery using several different measures
    1. Arteriography during surgery to be sure the vessel is open
    2. Angioscopy in which a flexible fiberoptic tube is placed inside the vessel with direct visualization of the operated area
    3. Color flow Doppler exam of vessels during surgery
  • Laser therapy and atherectomy (a special motor driven device to remove plaque from vessel wall) are endovascular procedures that have not been found to be beneficial at this time
  • Thrombolysis involves the injection of clot busting medication into clotted blood vessels and occluded grafts. This procedure will open up blood vessels, which then can be studied by arteriography. The clot busting medications are Streptokinase, Urokinase and rt-PA (recombinant tissue-type plasminogen activator)
Figure 8 - Left. Preoperative angiogram showing stenosis of the femoral artery. Middle. Balloon and stent in place. Right. Postoperative angiogram showing correction of the stenosis with a stent. Courtesy S. Sadiq, MD

Complications

Postoperative complications include:

  • Bleeding from vein donor site or bypass sites
  • Wound or graft infection
  • Urinary tract infection
  • Thromophlebitis - clots developing in veins that may lead to a pulmonary embolus in which a clot goes to the lung
  • Early graft occlusion due to clotting
  • Compartment compression syndrome in which there is excessive pressure in the muscle compartments due to swelling and causes ischemia of the muscles
  • Poor wound healing
  • Late graft failures occur due to progressive atherosclerosis and scarring and thickening of the intima
  • A heart attack, heart failure or stroke may occur during or after a bypass since the same process, which causes plaque to build up in the leg arteries is also present in the arteries of the heart (see cardiac catheterization) and brain
  • Pneumonia
  • Kidney failure
  • Failure of the surgical wounds to heal
  • Death

Care After Surgery

  • Blood pressure, pulse rate, respiration, temperature and urine output are closely followed
  • The leg is frequently checked for signs of ischemia, graft occlusion and swelling
  • Most patients eat and drink the day of surgery
  • Antibiotics and possibly anticoagulants (blood thinners) may be continued
  • Medications taken before surgery are usually continued
  • Most patients walk within 24-48 hours
  • Frequently anti platelet aggregating medications (Aspirin, Persantin, others) that reduce clotting are given
  • Discharge usually 4-7 days

Follow Up

  • The surgeon is seen the office in 5-10 days
  • Continue with prescribed medications
  • The condition of the graft, angioplasty or stent needs to be followed (usually by color flow Duplex ultrasound, a high grade stenosis will probably need arteriography)
  • The patient should be closely followed by other attending physicians to lower risk factors such as heart disease, stroke, kidney disease, eye disease, hypertension, diabetes and high cholesterol and lipids