Continue to scan slightly more distal from the popliteal vein to find its trifurcation.
Compress the popliteal vein periodically until you find where the popliteal vein trifurcates into the anterior tibial, peroneal, and posterior tibial veins. This junction signals the end of the examination.
Slide the probe 1-2 cm down the patient’s leg to find where the CFV branches into the deep femoral vein and (superficial) femoral vein.
At this point, the deep femoral vein will dive deep in the thigh. However, the (superficial) femoral vein will travel alongside the femoral artery.
Compress the (superficial) femoral vein just distal to the bifurcation.
Optional: though the 3-point ultrasound protocol only requires you to compress just distal to the bifurcation, you can also periodically check for clots in the rest of the (superficial) femoral vein using compression as you gradually move the probe inferiorly and medially towards the popliteal fossa where the (superficial) femoral vein dives into the adductor canal.
In this section, we will go over a step-by-step ultrasound approach to evaluate for deep vein thrombosis by visualizing the veins and using venous compression using a standard DVT Ultrasound Protocol.
It is important to note that there are several published protocols using anywhere from a 2-point ultrasound scan to a whole leg scan. We have found a 3-point compression ultrasound protocol to be most feasible while maintaining similar sensitivity and specificity when compared to a whole leg scan (Lee, Lee & Yun). We will focus on performing the 3-Point Ultrasound scan in this post, but here are the differences between the protocols that you may encounter:
2-Point Lower Extremity DVT Ultrasound: compression ultrasound including the femoral vein 1 to 2 cm above and below the saphenofemoral junction and the popliteal vein up to the calf veins confluence.
3-Point Lower Extremity DVT Ultrasound: compression ultrasound including the femoral vein 1 to 2 cm above and below the saphenofemoral junction, 1 to 2 cm above and below the bifurcation of the common femoral vein into the deep femoral vein and the (superficial) femoral vein, and lastly the popliteal vein up to the trifurcation into the anterior tibial vein, the posterior tibial vein, and the peroneal vein (Garcia 2018).
Whole Leg/Complete Lower Extremity DVT Ultrasound: involves scanning the leg using compression, color Doppler, and pulse wave Doppler from the common femoral vein all the way to the ankle while evaluating the calf veins.
Proper Vein Compression Technique
One of the biggest issues with performing DVT ultrasound is knowing how much to compress the vein. If the operator does not apply enough pressure or if the ultrasound probe is not perpendicular, these can lead to false positives for DVTs.
You should apply pressure until the pulsatile artery compresses slightly. If the adjacent vein compresses completely, there is no DVT. Refer to the figure below for an example of proper technique. If the vein does not compress completely, it is likely the patient has a clot in that region.
Note: There is a theoretical risk of dislodging a clot and causing a pulmonary embolism with compression. This is a rare complication, but something you should be aware of.
The venous anatomy of the lower extremity is fairly simple. Going from proximal to distal, here are the most important veins in the leg you will need to know for DVT ultrasound:
Common Femoral Vein (CFV)
Great Saphenous Vein
Bifurcation of CFV into Femoral Vein (previously named Superficial Femoral Vein) and Deep Femoral Vein
Trifurcation of the Popliteal Vein
Anterior Tibial Vein
Posterior Tibial Vein
The most proximal vessel is the Common Femoral Vein (CFV), which gives off an important superficial branch known as the great saphenous vein. The CFV continues on to give off a deep femoral vein, and a femoral vein.
Editor’s Note: The Femoral Vein is also previously known as the Superficial Femoral Vein. Don’t be misled by the name – the (superficial) femoral vein is actually part of the deep venous system. A study from 2011 showed that 75% of junior clinicians believed this vein was a part of the superficial venous system (Thiagarajah, Venkatanarasimha & Freeman). A clot in the (superficial) femoral vein is in fact a deep vein thrombosis and requires anticoagulant therapy to prevent a pulmonary embolus. Don’t get confused by the nomenclature!
As the femoral vein travels inferiorly and medially, it enters into the adductor canal and passes posterior to the knee to become the popliteal vein. At the level of the calf, the popliteal vein gives rise to three other deep veins: the anterior tibial vein, the posterior tibial vein, and the peroneal vein (Zitek, Baydoun & Baird).