A suprapatellar plica is a membrane - possibly an embryonic remnant - that stretches across the joint cavity in the pouch above the kneecap.
Here the patella (kneecap) has been cut from its tendon and lifted up to show the region at the top of the joint. You can see the curved suprapatellar plica above the patella.
X-ray from the side showing the position (yellow arrow) of the suprapatellar plica. The plica may easily be missed on X-ray but may show up as a thin structure if there is fluid in the knee (which shows as white).
A traumatised and thickened SPP can get trapped between the femur and the quadriceps, where it can cause ongoing pain. Sometimes this is mistaken as quadriceps muscle or tendon injury.
Anatomy of the suprapatellar plica
Commonly a supra patellar plica is a curved band along one wall of the capsule above the kneecap. Rarely it may reach right across as a full membrane from one side of the supra patellar pouch to the other, dividing it in two, sometimes with a little window in the middle.
How the suprapatellar plica causes symptoms
As a plica the suprapatellar plica is quite common, but as a symptomatic disorder it is actually quite rare. In disorders of the suprapatellar plica patients may complain of pain in the area above the kneecap, generally related to a prior episode of blunt trauma to this region.
CLINICAL PUBLICATIONS
Treatment of Pathological Synovial Plicae of the Knee. Camanho GL. Clinics (Sao Paulo). 2010 Mar; 65(3): 247–250.
An arthroscopic technique of demonstrating the pathomechanics of the suprapatellar plica. Strover AE, Rouholamin E, Guirguis N, Behdad H. Arthroscopy. 1991;7(3):308-10.
Suprapatellar plica classification and suprapatellar plica syndrome. Akao M, Ikemoto T, Takata T, Kitamoto K and Deiea M. Asia Pac J Sports Med Arthrosc Rehabil Technol. 2019 Jul; 17: 10–15.
See also -
eBook - An overview of plica problems in the knee
An expert look at the various plical folds of the knee and the problems that can be caused by a troublesome plica.