With knee POCUS you can diagnose effusions, septic arthritis, meniscal and ligament injuries and more.
The DVT exam at the bedside can be completed in under 10 minutes. It involves identifying three zones in the leg and performing compression at that site. The arteries and veins of interest run parallel with each other down the leg. In a leg with no DVT, both the vein and the artery will compress with adequate pressure. If a DVT is present, the artery will partially collapse but the vein will not.
Physician obtained DVT exam of the thigh with 3-zone compression has been consistently shown to have comparable accuracy to a sonographer. The sensitivity ranges from 86-100% and specificity over 95%. Exam below the knee is less sensitive, and usually not treated with anticoagulation, and therefore the DVT exam is limited to above the knee.
Patient & probe positioning
A high frequency transducer is tyically used to get higher resolution for superficial structures. The patient should be supine for anterior structures, prone for posterior structures.
Zone 1: Common Femoral vein to Greater Saphenous vein Junction
The external iliac artery and vein travel down the leg and change names to the common femoral artery and vein after crossing the inguinal ligament.
Starting as high as you can get in the inguinal crease, identify the common femoral vessels. They are usually large and running parallel. Artery will be lateral, vein medial.
Compress every 1-2 cm making sure the vein walls fully collapse and the arterial wall 'winks.' Travel down until you hit the greater saphenous vein, which will look like a snake-like projection coming out of the femoral vein at the 2 o'clock position.
Zone 2: Femoral Vein and Artery from Greater Saphenous Vein to Adductor Canal
After branching of the greater saphenous vein, the vessels change their name to the Femoral Vein and Femoral Artery. They run parallel with the artery on top.
Continue to follow them down the leg, compressing every 1-2 cm until they dive posteriorly through the Adductor Canal.
Zone 3: Popliteal vein and artery after exiting adductor canal posteriorly
After diving deep through the adductor canal to the posterior side of the leg, the vessels change their name to the popliteal artery and vein and switch positions, with the vein on top.
Either place the patient in prone position or have them bend their knee and frog-leg it out to access the popliteal fossa. Remember that the vein is now on top.
Positive Study Examples
If there is in fact a DVT in one of the veins examined, it will not be compressible. Depending on the chronicity of the clot, the echogenicity will differ. In general the more chronic a clot, the more hyperechoic but this is not a hard and fast rule.
In this example of a popliteal dvt exam, the artery (the posterior vessel)"winks" indicating enough pressure has been placed on the compression, yet the popliteal vein does not collapse. You can also see hyperechoic material inside the lumen of the vein.