Clark J M
Radiology. 1975 May;115(2):480-1. doi: 10.1148/115.2.480.
A lateral view of the knee in 90 degree flexion can reveal popliteal cysts which do not show on routine arthrography. Flexion causes transfer of intra-articular fluid to the posterior portion of the joint space, lowering pressure within the cyst and allowing it to fill with contrast media.
