Plica Syndrome is a painful knee condition due to a synovial plica becoming a source of pain due to an increase in volume and decrease in elasticity. The medial plica is the most commonly symptomatic. The diagnosis is not easy and the best treatment is unknown.
The plicae are embryonic remnants of the normal joint compartment separations that fold inwards and are present in most knees. They are considered to be duplications of the synovial membrane.
They are normally a thin (almost transparent), vascular, and pliable band of tissue. They originate from the synovial lining and cross the synovial joint.
Plicae can be found in the suprapatellar, medial, infrapatellar, or lateral compartments of the knee.
Suprapatellar plica - found between the suprapatellar bursa and the knee joint.
Medial plica (synonyms: medial shelf, plica synovialis mediopatellaris, plica alaris elongata, lion's bands, or Aoki edge) - originates from the medial wall of the knee joint, runs down and around the medial femoral condyle, and inserts into the synovium around the infrapatellar fat pad. They can be absent, vestigial, shelf-life, reduplicated, fenestrated, and high-riding.
Infrapatellar plica (synonym: ligamentum mucosum) - originates from the intercondylar notch and inserts into the synovium around the infrapatellar fat pad.
Lateral plica - this is very rare.
The Sakakibara classification scheme divides plica into four types:
- Type A: cord-like
- Type B: narrow, shelf-like that does not come into contact with the medial femoral condyle
- Type C: large with a shelf-like appearance
- Type D: fenestrated (central defect) that makes contact with the anterior surface of the medial femoral condyle.
The prevalence is unknown. It is most commonly reported in runners.
- Direct blunt trauma
- Repetitive injury
- Irritation from another knee abnormality such as osteochondritis dissecans or inflammatory arthritis
- Abnormal knee valgus
Through an inflammatory process, a plica changes from asymptomatic to symptomatic. It becomes fibrotic, avascular, and inelastic. Essentially it increases in volume and loses its elasticity. It can even become hyalinised.
This taut nonpliable band can rub or bowstring over the medial femoral condyle or it can become trapped between the patella and femoral condyle causing impingement. The articular cartilage of the medial femoral condyle and/or medial facet of the patella can become fragmented or fibrillated.
The medial plica is most commonly symptomatic, and type D (fenestrated) is the most commonly implicated.
The clinical features are often very similar or identical to other intra-articular knee pathologies.
The symptoms are usually nonspecific anterior or anteromedial knee pain (parapatellar), often following direct trauma or a repetitive injury.
The pain is often worse with sitting for long periods (called the theatre sign) or after sleeping. It is also often worse with squatting, kneeling, or walking upstairs. '
There may be mechanical symptoms such as clicking, catching, clunking, grinding, giving way, or popping with knee flexion and extension.
On examination for medial plica syndrome there may be slight swelling medial to the patellar margin, but there is no frank effusion.
The plica fold is located around the joint lines in the anterior knee compartment. The plica feel like a ribbon of tissue which can be rolled over the medial femoral condyle. The band of tissue runs either parallel or at a slight oblique angle to the medial border of the patellar. Flexing the knee to 90 degrees may make this easier to palpate. Record any tenderness.
Special tests have wide range of reported sensitive and specificity.
Medial patellar plica test: Sensitivity 90% and specificity 89% (one study of 172 knees). The patient is supine. Apply pressure over the inferomedial border of the patellofemoral joint with the thumb. This pushes the plica between the medial patella and medial femoral condyle. Maintain the pressure and passively flex the knee from 0 to 90 degrees. A positive test is provocation of pain at this extended position that is relieved at 90 degrees of flexion. During flexion the plica slips away from the medial condyle.
Hughston's plica test: The patient is supine with a relaxed extended knee. Place one hand around the heel and the palm of the other hand over the lateral patella border with fingers over the medial femoral condyle. Passively flex and extend the knee while internally rotating the tibia and pushing the patella medially. A positive test is pain and/or popping in the knee, usually at 30-60 degrees towards extension.
Strutter test: The patient is seated with the knee flexed to 90 degrees. Place two fingers over the centre of the patella. The patient actively extends their leg. A positive test is the patella jumping or stuttering during extension, usually at 45-70 degrees of extension.
A full knee examination should also be performed.
The main role of imaging is to exclude other conditions. Investigations are also done to investigate for possible causes of plica irritation - patella subluxation, osteochondritis dissecans, fractures, chondromalacia, etc. Inflammatory arthritis should also be considered.
Arthrography, ultrasound, and MRI are all unreliable at identifying abnormal plicae. MRI has a sensitivity of 77% and specificity of 58%. Ultrasound is superior to MRI with a sensitivity of 77% and specificity of 83%. Interestingly the medial patellar plica test is far superior to MRI, and slightly superior to ultrasound.
Investigations are not required for the initial diagnosis and management.
Arthroscopy is the gold standard for diagnosis.
The diagnosis of plica syndrome is not easy owing to the similarities in clinical presentation to various more common knee pathologies.
- Meniscal Knee Injuries - usually an acute event, mechanical symptoms more common, effusion, positive meniscus provocation tests. But McMurray may be positive in plica syndrome.
- Patellar Subluxation - usually more giving way, pain both medial and lateral. Tenderness more often along medial patella edge or adductor tubercle. Positive apprehension test.
- Hoffa fat pad syndrome
- Patellofemoral Joint Osteoarthritis (but can co-exist) - positive grind test
- Patellofemoral Pain Syndrome - doesn't usually have mechanical symptoms, and pain localised to the medial or lateral patellar facets in extension.
- Snapping ITB syndrome (but can co-exist, usually lateral)
- Ligament instability, such as ACL, MCL
- Patellar Tendinopathy - usually in a running or jumping sport, positive Royal London Hospital test.
- Pes Anserinus Pain Syndrome - pain and tenderness at anatomical pes
- Osteochondritis Dissecans - knee radiographs or MRI can help to distinguish.
- Pigmented villonodular synovitis
- Inflammatory arthritis (but can co-exist)
There is limited evidence to guide best treatment. Activity modification, analgesia, limb strengthening, supportive foot wear, taping, weight reduction when relevant, and knee joint corticosteroid injection may be considered.
Surgically the plica can be removed but this should only be done when all other causes are excluded and the patient has had an adequate trial of conservative management because incompletely resected plicae can fibrose can cause symptoms.
The plicae were first described by the anatomist Andre Vesalius
Papers of particular interest have been highlighted as: ◆ of special interest ◆◆ of outstanding interest
- Barber, F. A. (1987). "Fenestrated medial patella plica". Arthroscopy: The Journal of Arthroscopic & Related Surgery: Official Publication of the Arthroscopy Association of North America and the International Arthroscopy Association. 3 (4): 253–257. doi:10.1016/s0749-8063(87)80119-6. ISSN 0749-8063. PMID 3689523.
Lee, Paul; Nixion, Amy; Chandratreya, Amit; Murray, Judith (2017-01). "Synovial Plica Syndrome of the Knee: A Commonly Overlooked Cause of Anterior Knee Pain". The Surgery Journal (in English). 03 (01): e9–e16. doi:10.1055/s-0037-1598047. ISSN 2378-5128. PMC 5553487. PMID 28825013. Check date values in:
|date=(help)CS1 maint: PMC format (link)
- Stubbings, Nicholas; Smith, Toby (2014-03). "Diagnostic test accuracy of clinical and radiological assessments for medial patella plica syndrome: a systematic review and meta-analysis". The Knee. 21 (2): 486–490. doi:10.1016/j.knee.2013.11.001. ISSN 1873-5800. PMID 24280039. Check date values in:
- Genc, Erdinc; Duymaz, Tomris (2021-02-10). "Functional effects of kinesiology taping for medial plica syndrome: a prospective randomized controlled trial". Physiotherapy Theory and Practice: 1–10. doi:10.1080/09593985.2021.1885089. ISSN 1532-5040. PMID 33567953.
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