A medial plica or medial shelf is a remnant of an embryonic partition in the knee, and runs along the inner aspect of the kneecap.
Page updated February 2024 by Dr Sheila Strover (Clinical Editor)
Does everyone have a medial plica?
Some evidence of the original embryonic plical fold can be seen in most people, but it is generally small and flimsy.
In some people it may be much sturdier and be referred to as 'medial shelf' - more a vertical shelf than a horizontal one, mind - and runs down from above the patella to the fat pad below the patella.
Quote from peer-reviewed paper:
"....Since the treatment of a painful plica after an arthroscopic resection can often cause patients to have more pain than they did prior to the arthroscopic resection, it is important to make sure that a patient has pathology of this area which is not responsive to an exercise program, and possibly injections, prior to consideration of resection of this tissue"
Citation: Griffith CJ, LaPrade RF. Medial plica irritation: diagnosis and treatment. Curr Rev Musculoskelet Med. 2008 Mar;1(1):53-60. doi: 10.1007/s12178-007-9006-z. PMID: 19468899; PMCID: PMC2684145.
What causes a medial plica to sometimes make a snapping noise?
As the knee bends the 'shelf' of tissue may also give a sudden snap over the rounded ends of the femur bone. If it has been traumatised, and has become thickened and rigid, the snapping may become chronic and the examiner may be able to feel a 'stutter' in that area as the knee is bent and straightened.
Does a medial plica always cause pain?
A medial plica is often an incidental finding on arthroscopy or MRI. Only some of them become symptomatic. This has unfortunately led to the finding being dismissed during the investigation of anterior knee pain.
Quote from peer-reviewed paper:
"The fact that patients with plica syndrome show a low [quality of life - QOL] score emphasizes the importance of awareness toward plica syndrome that remains an underdiagnosed cause of anterior knee pain and which has significant impact on QOL...."
Citation: Sauer S, Karlsen G, Miller L, Storm JO. Medial Plica Syndrome of the Knee: Arthroscopic Plica Resection versus Structured Physiotherapy-A Randomized Controlled Trial. Surg J (N Y). 2022 Sep 19;8(3):e249-e256. doi: 10.1055/s-0042-1756183. PMID: 36131946; PMCID: PMC9484868.
How does a medial plica cause pain?
Besides anterior knee pain, snapping and a localised 'stutter', some patients may experience a sharp pain when the knee is in a certain position because the plica can become nipped between the femur and the patella. Recurrent nipping traumatises and thickens the plica.
The inset in the illustration on the right is a photograph taken during arthroscopy of a medial plica. The camera (arthroscope) is in the suprapatellar pouch, looking down on the top of the patella. You can see the thickened plica becoming nipped between the patella (above) and the femur (below) - as demonstrated in the illustration.
When a medial plica becomes abnormally thickened, it can be felt with the finger as a string-like object to the inner aspect of the kneecap. Such a pathological (abnormal and symptomatic) plica is something that a surgeon should examine for, because in the right patient symptomatic relief can be immediate after its removal.
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A discussion about plica syndrome