Plica Syndrome.

The knee joint is composed of three separate synovial compartments, the medial and lateral compartments, and the suprapatellar pouch. A thin membrane separates these compartments embryologically, but these membranes involute in the twelfth week of foetal growth, so that the synovial compartments join. If this process does not occur, the synovial folds convert into a plica.

There are three potential synovial folds in the knee joint;

(1) the suprapatellar plica, which separates the suprapatellar pouch from the knee joint (present to some extent in 89% of cadaver dissections);
(2) the mediopatellar plica is the plica with possible pathological relevance as it becomes tight as the knee is flexed. If it has a semi-lunar shape it may cause symptoms by impinging between the medial patellar facet and the medial femoral condyle. It arises from the medial aspect of the knee joint and runs obliquely down to insert into the synovium covering the fat pad; and
(3) the infrapatellar plica, which runs from the ligamentum patellae to the intercondylar notch.

Plicae vary in size to a considerable extent. Most, especially the smaller plicae, are probably irrelevant clinically. Some, especially the larger ones, are implicated as causes of acute knee pain. The mechanism of pain generation is not certain. It is believed that a plica may become swollen and painful as a result of haemorrhage (in children) or inflammation after trauma, or may undergo inflammation caused by other intra-articular pathology. Further mechanical pain may be induced as the inflamed plica is stretched across a femoral condyle, usually the medial, when the knee flexes. This process can produce medial knee pain that can arise from the patella, the medial condyle, or the plica itself.

Plica as a consequence of trauma has been found in 13% and 50% of cases. Histological analysis of plicae has revealed fibrosis and haemorrhage.



Hughston et al. considered the incidence of plicae in the normal population to be 20%. Iino reported an incidence of plica of over 50% in 67 adult cadaver knees. Plicae are seen in between 40 and 80% of arthroscopies.


Controversy exists as to the extent to which plicae cause symptoms. Some, including Iino, Reid et al, Fairbank et al and Dugdale and Barnett consider the plica to be a potentially common source of anterior knee pain, especially in adolescents, whilst others, including Broom and Fulkerson and Lupi et al, consider the syndrome to be over diagnosed. The condition is most frequently diagnosed at arthroscopy.

The indication for the arthroscopy includes symptoms that may mimic patellofemoral joint pain, such as anterior or anteromedial knee pain, catching, and swelling, or mimic meniscal problems, such as pain, locking and giving way. The diagnosis is then by exclusion. If a plica is present and large in the absence of other obvious pathology, then it might be the cause of the presenting symptoms. The plicae are described, in one series by Johnson et al, as palpable in 70% cases.

Sherman and Jackson suggested the following criteria for the diagnosis of plica:

(1) appropriate history;
(2) failed conservative treatment;
(3) at arthroscopy, plica with an avascular fibrotic edge impinging on the medial femoral condyle during flexion, and
(4) no other intra-articular pathology of possible relevance.

Acute tears of a plica are rare, but they may produce an acute haemarthrosis. In the study of Lupi et al., 42 patients with arthrograms demonstrating a plica were seen. Twenty-four of these were considered asymptomatic for “plica syndrome’, and 14 patients had other pathology at arthroscopy, such as chondromalacia patellae, meniscal injury, and a torn ACL. Sixteen were treated for the ‘plica syndrome’ with arthroscopy or surgical excision.

Klein reviewed 1328 arthroscopies, at which 180 medial patellar plicae were present. Forty-three of these underwent arthroscopic surgery to the plica. Of these 43, 28 had abnormalities of the plica including thickening, fibrosis and lack of elastic function. In 13 there was apparent impingement of the plica between the medial femoral condyle and the patella. Fibrosis was documented in some by biopsy.

Nottage et al. documented the presenting complaints in patients eventually diagnosed as having a symptomatic plica as (N = 78) anteromedial knee pain (65%), crack/pop/snap (50%), weak/give-way (42%), tight sensation (23%), painful repetitive activity (22 %), medial joint line pain (21%), and lateral joint line pain, pain on inclines, squatting pain and sitting pain all at less than 10%. Physical signs were medial plica tenderness (55%), positive Apley test (37%), positive McMurray test (27%), medial joint line tenderness (19%), positive patellar compression (18%), quadriceps atrophy over 1.25 cm (14%), and lateral joint line tenderness and effusion in less than 10% each.

Johnson et al found symptomatic plicae at an average age of 14 years. The pain was rated at severe or moderate in 89%, clicking was present in 93%, giving-way in 64%, and locking in 22%.


The major problem with the assessment of treatment of plica is the lack of diagnostic data. There are no randomised trials concerning the overall treatment of plicae. However, a robust study has demonstrated that arthroscopic debridement of plicae is better than placebo.

Aprin et al found that non-operative treatment was unsuccessful in patients with plica impingement demonstrated on arthrogram. Rovere and Adair reported that 73% of patients did well after putative intra-plical injection with local anaesthetic and corticosteroid. Klein reviewed 37 patients between 4 and 42 months after medial plica excision, and found good or better results in 62% of cases. In close to 50% of cases, other pathology was detected and treated.


Plicae may be a cause of anterior and anteromedial knee pain. However, the presence of a plica does not implicate it as a cause of pain. The diagnosis is made by excluding other causes of knee pain, although this often requires arthroscopy. When pain persists despite conservative treatment, there is evidence for surgical excision.


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Iino S. Normal arthroscopic findings in the knee joint of adult cadavers. J Jap Orthop Assoc 1939; 14:467-523.

Reid GD, Glasgow M, Gordon DA, Wright TA. Pathologic plicae of the knee mistaken for arthritis. J Rheumatol 1980; 7:573-576.

Fairbank JCT, Pynsent PB, van-Poortvliet J, Phillips H. Mechanical factors in the incidence of knee pain in adolescents and young adults. J Bone and Joint Surg 1984; 66B:685-693.

Dugdale TW, Barnett PR. Historical background: patellofemoral pain in young people. Orthop Clin North Amer 1986; 17:211-219.

Broom HJ, Fulkerson JP. The plica syndrome: a new perspective. Orthop Clin North Am 1986; 17:279-281.

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Sherman RM, Jackson RW. The pathological medial plica: criteria for diagnosis and prognosis. J Bone Joint Surg 1989; 71B:351.

Klein W. The medial shelf of the knee: a follow-up study. Arch Orthop Traumat Surg 1983; 102:67-72.

Nottage WM, Sprague NF III, Auerback BJ, Shahriaree H. The medial patellar plica syndrome. Am J Sports Med 1983; 11:211-214.

Aprin H, Shapiro J, Gerswind M. Arthrography (plica views): a non-invasive method for diagnosis and prognosis of plica syndrome. Clin Orthop 1984; 183:90-95.

Rovere GD, Adair DM. The medial synovial shelf plica syndrome. Treatment by intraplical steroid injection. Am J Sports Med 1985; 13:382-386.

The concepts presented here are entirely the author's own (unless expressly stated) and do not represent the thoughts or ideas of any other person.

© Charlie Kornberg. All rights reserved. No part of this web page, or related accompanying pages, may be reproduced without the prior permission of the Author.