“Popliteal cysts cause posterior knee pain, and are thought to be a result of increased intra-articular pressure forcing fluid into the bursa and causing expansion and subsequent pain. Risk factors include rheumatoid arthritis or osteoarthritis and advanced age. With the patient lying down, a mass can be palpated in the medial popliteal fossa while the knee is extended. When the knee is flexed to 45° the pain subsides and the
mass is reduced in size or disappears. Imaging is generally not needed for the diagnosis. Plain radiographs are obtained if there is a possible fracture. Ultrasonography can be used if deep vein thrombosis is a consideration. If significant internal derangement of the knee is suspected, MRI may be useful. An arteriogram would be an option if aneurysm
of the popliteal artery were suspected. Treatment is generally conservative, although addressing the underlying knee pathology will prevent the cyst from recurring. Pain is often decreased by keeping the knee in flexion and the use of ice and NSAIDs.
If this is not successful, intra-articular corticosteroids or cyst aspiration is often effective.” ABFM
Reference
J Fam Pract 2014;63(12):720-728.