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The popliteal artery is located behind the knee. Aneurysms (widening of the artery) can occur in this location. Patients rarely have any symptoms due to the aneurysm. It is usually discovered on routine physical examination by a physician. The cause of these aneurysms is unknown. They tend to occur in older men and women (more common in men) and occur in both legs about 50% of the time.
If a physician suspects the presence of a popliteal artery aneurysm, an ultrasound exam is usually ordered to confirm the presence of the aneurysm, determine the size, and look for the presence of clot within the aneurysm. Because of the abnormal swirling of blood within the aneurysm sac, blood clot usually forms along the inside wall of the aneurysm. Most of the time, popliteal artery aneurysms cause problems because the blood clot builds up to the point where it shuts down blood flow completely, or because some of the clot within the aneurysm travels down the artery and into the foot. Either of these two events can lead to the need for amputation of the lower leg and foot. This is what makes popliteal artery aneurysms so dangerous. These types of aneurysms rarely rupture, although this can occasionally occur.
After confirmation of the presence of a popliteal artery aneurysm, a determination is made as to whether repair is necessary at that time. Each case is different and a decision must be made by the patient's physician as to whether repair is necessary or whether close follow up and careful observation is the better course. Many issues must be taken into consideration including the size of the aneurysm, condition of the arteries above and below the aneurysm, presence or absence of blood clot within the aneurysm, and the overall health of the patient who has the aneurysm.
Surgical repair is usually quite successful, durable, and can usually be performed with low risk. The best procedure for repair involves an incision on the leg, removal of the popliteal aneurysm and reconstruction of the blood flow to the foot using either a vein or an artificial artery. In recent years, some physicians have recommended stent grafts to repair popliteal aneurysms, particularly in patients who are "not good risks" for the more standard type of repair due to, for example, cardiac or pulmonary conditions. Most experienced vascular specialists regard stenting as a "second choice procedure" reserved for very high risk patients who may not be suitable candidates for open surgery. Stent graft popliteal aneurysm repair does not have the durability of an open repair and closure of the stent occurs in a substantial number of cases within a year or two after the stent is placed. Many specialists also have concerns about placing a metallic stent behind the knee where it will be subject to flexion of the knee joint.
Baker's cysts are collections of fluid in the back of the knee which can occasionally be confused with a popliteal artery aneurysm. A Baker's cyst is usually the result of a problem in the knee joint which is causing inflammation of the joint space. Examples are traumatic injuries to the joint or inflammatory conditions such as arthritis. Baker's cysts generally occur in adults over the age of 50, and its treatment consists of correcting the underlying problem in the knee joint which has led to the development of the cyst. Occasionally, the cysts become very large and can press on adjacent structures such as veins resulting in swelling of the entire leg below the knee. In situations such as this, the Baker's cyst is sometimes drained with a needle in order to relieve the pressure created by the cyst.