Basic anatomy of the lower extremity arteries
To appreciate how helpful ultrasound is in evaluating the lower extremities for abnormalities, it is important to be proficient in the basic anatomy of the lower extremity arteries.
There are five arteries in each leg that you’ll examine in a routine ultrasound study:
- Common femoral artery (CFA)
- Superficial femoral artery (SFA)
- Popliteal artery
- Posterior tibial artery (PTA)
- Dorsalis pedis artery (DPA)
The lower extremities’ deep veins run adjacent to arteries of the same name which can help identify the arteries on ultrasound.
Figure 1. The five lower extremity arteries that are routinely examined on ultrasound include the common femoral artery (CFA), the superficial femoral artery (SFA), the popliteal artery, the posterior tibial artery (PTA), and the dorsalis pedis artery (DPA).
The common femoral artery (CFA)
The saphenofemoral junction (SFJ) in the groin area is adjacent to the CFA. On ultrasound, you can find the SFJ next to the CFA with the common femoral vein (CFV) just inferior. This appearance is referred to as the Mickey Mouse sign.
Figure 2. Ultrasound image of the Mickey Mouse sign, which consists of the saphenofemoral junction (SFJ) adjacent to the common femoral artery (CFA), and the common femoral vein (CFV) just inferior.
The CFA is inferior to the inguinal ligament and receives aortoiliac inflow. On ultrasound, a normal CFA has smooth walls and a black lumen.
Figure 3. The common femoral artery (CFA) is located just inferior to the inguinal ligament. On an ultrasound image of a normal CFA using a longitudinal (e.g., lengthwise) view, the walls appear smooth and the lumen appears black.
At the CFA bifurcation, the CFA divides into two branches:
- Profunda femoris artery (PFA)
- Superficial femoral artery (SFA)
The profunda femoris artery (PFA)
The PFA, formerly known as the deep femoral artery, dives deep off of the CFA bifurcation and branches into collaterals in the thigh. Due to its deep anatomical location, it is not routinely examined on ultrasound past the CFA bifurcation. The PFA and its branches are better evaluated by computed tomography (CT), if needed.
Figure 4. The profunda femoris artery (PFA) is a branch of the common femoral artery (CFA).
The superficial femoral artery (SFA)
The other branch off of the CFA bifurcation, the SFA, is also known as the femoral artery. Rather than use the general terminology, it is more useful to clarify whether you’re referring to the common femoral artery, the profunda femoris artery, or the superficial femoral artery. The SFA travels from the CFA bifurcation down the medial thigh to the knee.
Figure 5. The superficial femoral artery (SFA), a branch of the common femoral artery (CFA), travels down the medial thigh to the knee.
The popliteal artery
The SFA becomes the popliteal artery at the posterior knee. The above-knee popliteal artery starts at the distal adductor canal (where the thigh becomes the knee), and the below-knee popliteal artery extends to the bifurcations of the calf arteries at the distal popliteal fossa.
The popliteal is the only artery where you regularly see the vein located above the artery on the ultrasound screen.
Figure 6. The superficial femoral artery (SFA) becomes the popliteal artery at the posterior knee. On ultrasound, the popliteal vein is often oriented superior to the popliteal artery.
The posterior tibial artery (PTA)
The distal popliteal artery splits into the anterior tibial artery (ATA) and the tibioperoneal trunk (TPT) at the distal popliteal fossa. The TPT immediately splits into the peroneal artery and PTA, which both travel the length of the inner calf to the ankle.
Figure 7. The distal popliteal artery branches into the anterior tibial artery (ATA) and the tibioperoneal trunk (TPT). The TPT immediately branches into the peroneal artery and posterior tibial artery (PTA).
The dorsalis pedis artery (DPA)
The ATA follows the lateral shin and becomes the DPA at the ankle. Then, it forms the pedal arch of the foot. The DPA can be evaluated in an ankle-brachial index test, known as the ABI test.
Figure 8. The anterior tibial artery (ATA) becomes the dorsalis pedis artery (DPA) at the ankle.
The three-vessel runoff
The peroneal artery, the PTA, and the ATA are commonly referred to as the three-vessel runoff. The three-vessel runoff isn’t typically examined throughout the entire calf with ultrasound.
By comparing the ultrasound duplex findings at the popliteal artery to the waveforms obtained at the ankle, we can determine the presence and severity of a disease in the calf. If there is a concern from this comparison, a CT scan is ordered for a more efficient and detailed assessment of the runoff vessels.
Figure 9. The arteries that form the three-vessel runoff include the peroneal artery, posterior tibial artery (PTA), and anterior tibial artery (ATA).
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