Popliteal artery entrapment syndrome is a complex and relatively rare problem. It involves the compression of the artery that runs behind the knee and this occurs most commonly during exercise. In some people the compression of this artery is normal and does not result in symptoms at all. For others however, this compression can result in similar symptoms as patients who have blockages in their arteries. The repeated compression of the popliteal artery with every step taken reduces the blood flow into the muscles of the calf and foot. This lack of oxygenated blood flow can cause pain and discomfort within the muscles below the knee. These symptoms are often described as intermittent claudication.
There are two main causes of popliteal artery compression.
Functional popliteal artery entrapment is the compression of the popliteal artery caused by hypertrophy (large muscle bulk) of the muscles in the upper calf and behind the knee.
Anatomical popliteal artery entrapment is the compression of the popliteal artery caused by an abnormally positioned artery or abnormally positioned muscle.
An important part of this ultrasound scan is exercise. It is essential that you bring clothing and footwear are suitable for running on a treadmill.
To begin with the sonographer will perform and ankle brachial pressure index. This is a simple but effective test which gives us a baseline of the blood pressures in all four limbs (both arms and legs). When you are lying down the pressure should be similar in both arms and both legs.
Next, the sonographer will do an ultrasound scan of the arteries in your legs from the groin to the ankle (you may need to remove your shorts/pants for this part). This is to check that you don’t have any unusual anatomy or blockages in your arteries. For the next part of the scan you will need to be standing so that the sonographer can image the arteries behind your knee whilst standing, they will measure the diameters of the artery and blood flow.
Next, whilst standing, the sonographer will ask you to perform a heel raise and hold, they will then take the same measurements of the artery to see if there is any change in the artery which indicates compression. Unfortunately, you will need to perform multiple heel raises so that the sonographer can look the whole segment of popliteal artery. Depending on any compression that is identified sometimes you will be asked to perform heel raises on one leg.
The final part of the scan is the exercise. The sonographer will ask to run on a treadmill and to try and reproduce the typical symptoms. When the exercise is completed you will need to lie down again on the couch and the sonographer will repeat the ankle brachial pressure index. This will demonstrate if there is any difference between the arm and leg pressure, if the pressure in the legs is lower than the arms then this could indicate that there is significant compression of the popliteal artery.
Dr Theivendran will need to clinically assess you in order to determine whether any compression that may be identified during the ultrasound scan is likely to be the cause of your symptoms. The popliteal artery entrapment ultrasound is just part of the process and you may be required to undergo further imaging (eg. MRI or CT). There are several differential diagnosis for the doctor to consider such as chronic exertional compartment syndrome, tibial stress fractures, nerve entrapment syndrome and lumbar disc herniation.