A plica is a band of thick, fibrotic tissue that extends from the synovial capsule of a joint. Plica can be present in multiple joints, but this article will review plica in the knee, the joints most commonly affected by plica tissue. As a result of overuse or injury, plica can become inflamed or irritated due to friction across the patella or the medial femoral condyle. When the plica becomes inflamed or irritated, it can cause plica syndrome, which is anterior knee pain due to the plica.
Plica syndrome is a condition that occurs when a plica (a vestigial extension of the protective synovial capsule of the knee) becomes irritated, enlarged, or inflamed.
Synovial plicae are synovial folds that may be found as intraarticular structures within the knee joint. They are remnants of incomplete resorption of mesenchymal tissue during fetal development. Synovial plicae, if present, are supposed to be non-pathological and asymptomatic, however, if they are exposed to special events like direct trauma or repeated activities, they may be inflamed and become fibrosed and rigid and irritates the synovium of the underlying femoral condyle resulting in secondary mechanical synovitis and chondromalacia leading to what is known as plica syndrome of the knee.
Types of Plica
In the knee, 4 types of plicae can be distinguished, depending on the anatomical location within the knee joint cavities: suprapatellar, mediopatellar, infrapatellar, and lateral plicae. The last one is rarely seen and, therefore, there is some controversy regarding its existence or its exact nature. The plicae in the knee joint can vary in both structure and size; they can be fibrous or fatty, longitudinal or crescent-shaped[rx].
- The suprapatellar plica also referred to as the plica synovial suprapatellar, superior plica, superomedial plica, medial suprapatellar plica, or septum is a domed, crescent-shaped septum that generally lies between the suprapatellar bursa and the tibiofemoral joint of the knee. It runs down from the synovium at the anterior side of the femoral metaphysis, to the posterior side of the quadriceps tendon, inserting above the patella.
- Its free border appears sharp, thin, wavy, or crenated in normal conditions. This type of plica can be present as an arched or peripheral membrane around an opening, called porta. It often blends into the medial plica. As the suprapatellar plica is anteriorly attached to the quadriceps tendon, it changes dimension and orientation when moving the knee.
Based on arthroscopic investigations the suprapatellar plicae can generally be classified by location and shape into different types. Kim and Choe (1997) have distinguished the following 7 types;[rx]
- Absent No sharp-edged fold.
- Vestigial Plica with less than 1 mm protrusion. Disappeared with external pressure
- Medial Plica lying on the medial side of the suprapatellar pouch
- Lateral Plica lying on the lateral side of the suprapatellar pouch
- Arch Plica present medially, laterally and anteriorly but not over the anterior femur
- Hole Plica extending completely across the suprapatellar pouch but with a central defect.
- Complete Plica dividing the suprapatellar pouch into two separate compartments
Medial patella plica
- The medial patellar plica is also known as plica synovial mediopatellaris, medial synovial shelf, plica alaris elongate, medial parapatellar plica, the meniscus of the patella or after its first two descriptors as Iion’s band or Aoki’s ledge. It is found along the medial wall of the joint.[rx]
- It attaches to the lower patella and the lower femur and crosses the suprapatellar plica to insert in the synovium surrounding the infrapatellar fat pad. Its free border can have different appearances. As the medial plica is attached to the synovium covering the fat pad and ligament patellae, it also changes dimension and orientation during knee movement. The medial plica is known to be the most commonly injured plica due to its anatomical location and it is usually this plica which is implicated when describing the plica syndrome.
Similar to the suprapatellar plicae, the medial plicae has also can be classified by appearance. Kim and choe have defined the following 6 types:[rx]
- Absent No synovial shelf on the medial wall
- Vestigial Less than 1 mm of synovial elevation which disappears with external pressure
- Shelf A complete fold with a sharp free margin.
- Reduplicated Two or more sheves running parallel. They may be of differing sizes.
- Fenestra The shelf contains a central defect
High-Riding A shelf like structure running anterior to the posterior aspect of the patella, in a position where I could not touch the femur.
Each type is subdivided according to size and relation to femoral condyle with flexion and extension of the knee into:
- A—Narrow non touch (never makes contact with the femoral condyle).
- B—Medium touch (touches condyle with knee movement).
- C—Wide covering (covers the femoral condyle).
- The infrapatellar plica is also called as ligamentum mucosum, plica synovial infrapatellaris, inferior plica or anterior plica. It is a fold of synovium which originates from a narrow base in the intercondylar notch, extends distally in front of the anterior cruciate ligament (ACL), and inserts into the interior of the infrapatellar fat pad.
- It is often difficult to differentiate the infrapatellar plica from the ACL. Mostly it appears as a thin, cord-like, fibrous band. The infrapatellar plica is considered to be the most common plica in the human knee. Discussion is on-going whether this plica is structurally important to regular knee movement or whether it is redundant.[rx]
A classification for infrapatellar plicae can be as follows:[rx]
- Absent No synovial fold between the condyles of the femur.
- Separated A complete synovial fold that was separate from the anterior cruciate ligament (ACL).
- Split Synovial fold that is separate from the ACL but is also divided into two or more cords.
- Vertical septum A complete synovial fold that is attached to the ACL and divided the joint into medial and lateral compartments.
- Fenestra A vertical septum pattern that contains a hole or defect.
- The lateral plica is also known as plica synovialis lateralis or lateral para-patellar plica. It is longitudinal, thin and is located 1-2 cm lateral to the patella. It is formed as a synovial fold along the lateral wall above the popliteus hiatus, extending inferiorly and inserting into the synovium of the infrapatellar fat pad.
- Some authors doubt whether it is a true septal remnant from the embryological phase of development or whether it is derived from the parapatellar adipose synovial fringe. [rx]
This type of plica is only seen on rare occasions; its incidence being well below 1%
Causes of Plica syndrome
- This inflammation is typically caused by the plica being caught on the femur or pinched between the femur and the patella. The most common location of plica tissue is along the medial (inside) side of the knee. The plica can tether the patella to the femur, be located between the femur and patella, or be located along the femoral condyle. If the plica tethers the patella to the femoral condyle, the symptoms may cause it to be mistaken for chondromalacia.
- The plica themselves are remnants of the fetal stage of development where the knee is divided into three compartments. The plica normally diminishes in size during the second trimester of fetal development, as the three compartments develop into the synovial capsule.
- In adults, they normally exist as sleeves of tissue called synovial folds. The plica are usually harmless and unobtrusive; plica syndrome only occurs when the synovial capsule becomes irritated, which thickens the plica themselves (making them prone to irritation/inflammation, or being caught on the femur).
Symptoms of Plica
- Symptoms of plica syndrome are often similar to many other etiologies of knee pain. As a result, the differential diagnosis can be lengthy and may include osteochondritis dissecans, patellofemoral syndrome, patellofemoral subluxation, meniscal disease, osteoarthritis, patellar tendonitis, cruciate ligament pathology, and pigmented villonodular synovitis. These differential diagnoses can be differentiated from plica syndrome as follows:
Other symptoms of knee plica syndrome can also include the following
- a catching or locking sensation on the knee while getting up from a chair after sitting for an extended period of time,
- difficulty sitting for extended intervals,
- a cracking or clicking noise when bending or stretching the knee,
- a feeling that the knee is slowly giving out,
- a sense of instability on slopes and stairs,
- and may feel swollen plica when pushing on the knee cap.
Diagnosis of Plica
As the symptoms experienced with pathological plicae are not specific, the diagnostic procedure should keep a high level of suspicion and ideally work through exclusion, to differentiate from any other knee derangement.[rx]
- Physical examination – not give exclusive results due to possible tenderness of the anteromedial capsule or the area around the suprapatellar pouch on direct palpation.
- Provocation test – Provocation test which simulates conditions that can lead to the occurrence of symptoms could be applied. These results will be considered positive if the symptoms resulting from the tests are similar to the symptoms the patient is usually experiencing. Yet as similar symptoms may also be associated with other conditions of the knee joint, this method will not give an unambiguous result either.
- Radiography will be of no diagnostic – value to determine whether patients suffer from plica syndrome, as the radiograph will be negative. Yet, radiography can be helpful to rule out other syndromes where the symptoms are common with those of a plica syndrome (see differential diagnosis). If there is symptomatic plicae, it will demonstrate hypertrophy and inflammation. This will lead to thickening and eventually fibrosis. If the fibrosis is significant, changes in the articular surface and the subchondral bone may occur.
- Arthroscopy – can be helpful because plica syndrome is often confused with chondromalacia or a medial meniscal tear. Lateral pneumoarthrography and double-contrast arthrography have been used with varying success. In combination with CT, it can not only visualize the plica, but it also demonstrates whether or not impingement is present. However, currently, it has gone out of use because of problems to obtain reproducible and reliable results and the exposure to radiation.[rx]
- Nowadays, the best results are obtained through MRI Scans – Most cases of plica syndrome do not absolutely require MRI, but it can help to rule out other pathologies that can cause knee pain. An MRI can exclude bone bruises, meniscus tears, ligament injuries, cartilage defects, OCD lesions,… that may masquerade as plica syndrome. MRI is useful to evaluate the thickness and extension of synovial plicae and it can also detect a pathologic plica, particularly if an intra-articular effusion is present.[rx]
- Osteochondritis dissecans – Differentiate with radiographs and MRI.
- Patellofemoral syndrome – Patellofemoral knee pain can be difficult to distinguish from plica syndrome as the symptoms overlap significantly. Other causes of patellofemoral pain, such as chondromalacia, may be apparent in history and imaging.
- Patellofemoral subluxation – Differentiate because patients with a patellofemoral subluxation will often provide a history consistent with subluxation and may have apprehension with a displacement of the lateral patella.
- Meniscus pathology – Differentiate because meniscus pathology will have tenderness in the joint line, whereas plica pain tends to localize above the joint line. Also, physical exam tests such as Apley, Thessaly, bounce home, and/or McMurray can help distinguish the 2 entities.
- Osteoarthritis – Differentiate with radiographs showing decreased joint space, osteophytes, subchondral sclerosis, subchondral cysts, among others, although this does not rule out also having symptomatic plicae.
- Patellar tendonitis – Differentiate by palpating the patellar tendon on either the proximal or distal attachment.
- Cruciate ligament dysfunction – Differentiate by physical exam techniques suggesting laxity including Lachman, anterior drawer, or posterior drawer would likely be positive in cruciate ligament injury.
- Pigmented Villonodular Synovitis (PVNS) – Differentiate via MRI.
Medial plicae are most commonly symptomatic and can be classified by the Sakakibara arthroscopic classification:
Type A – Elevation in the synovial wall
Type B – Appear shelf-like, but not covering the anterior surface of the medial femoral condyle
Type C – Large, shelf-like appearance and covering the anterior surface of the medial femoral condyle
Type D – Fenestrated plica with a central defect.
Treatment of Plica
Treatment options for plica syndrome include stretching and strengthening, intrapleural corticosteroid injections, and arthroscopy.
The Sakakibara classification system is important when considering treatment because type A and B have a low likelihood to cause pain. Type C and D, on the other hand, can impinge on the medial condyle due to their larger size. Type A and B respond much better to conservative therapies than C and D do. As a result, patients with type A and B should be encouraged to attempt conservative therapy first.
Conservative treatment for plica syndrome can either be performed at home by the patient or via formal physical therapy. Either way, this would involve lower extremity stretching and knee extension exercises with the goal of strengthening the joint capsule musculature, hamstrings, and quadriceps. NSAIDs and ice are reasonable treatments at this stage to calm down inflammation. Conservative management also includes avoiding activities that incite pain. At least 3 months of conservative treatment is recommended before advancing to more aggressive therapies. One study demonstrated that 49 of 55 patients treated conservatively returned to their prior baseline without a return of symptoms. The remaining 6 patients were also able to return to their prior baseline, but they reported an occasional return of symptoms, which were tolerable.[rx]
Often the next step if stretching and strengthening do not release symptoms is intrapleural corticosteroid injection. This is a reasonable treatment option, especially early in the disease process when conservative management has not provided relief. Research of 31 patients with medial plica syndrome treated with intrapleural steroid injection found that 73% had a full return to activity with complete pain relief.[rx]
Resection via arthroscopy is a favorable option for medial plicae that do not respond to conservative treatment. Resection is also reasonable when cartilage damage is suspected, such as in type C and D lesions, even if conservative measures have not been completed for 3 months. Another study showed that compared to conservative treatment, arthroscopy yields a greater therapeutic effect for plica syndrome and the effect is longer lasting.[rx]
Physical Therapy Management of Plica
- Conservative treatment of the synovial plica syndrome first consists of pain relief with NSAIDs and repeated cryotherapy during the day using ice packs or ice massage, to reduce the initial inflammation. Other measures will include limiting aggravating activities by changing the daily physical movements to reduce repetitive flexion and extension movements and by correcting biomechanical abnormalities (tight hamstrings, weak quads).
- Additionally, microwaves diathermy, phonophoresis, ultrasound, and/or friction massage might be considered. Friction massage is also used in this therapy to break down scar tissue. Occasionally, immobilization of the knee in the extended position for a few days can be helpful, as well as avoiding maintenance of the knee in a flexed position during longer periods.[rx]
- Once the acute inflammation is reduced, physical therapy can be initiated, aiming at decreasing compressive forces by stretching exercises and by increasing quadriceps strength and hamstring flexibility.[rx]
- This treatment is usually recommended for the first 6-8 weeks after the initial examination.[rx]
- It consists of strengthening and improving the flexibility of the muscles adjacent to the knee, such as the quadriceps, hamstrings, adductors, abductors, M Gastrocnemius, and M Soleus. [rx][rx]
The key components of the rehabilitation program will involve flexibility, cardiovascular condition training, strengthening and return to ADL.
- An exercise to regain flexibility in extension is the supine passive knee extension exercise while placing a foam roller under the ankle. Gravity will help to stretch the knee in maximal extension. If possible you can make the exercise more difficult by putting weights on the anterior sight of the knee.[rx]
- Quadriceps sets[rx]
- Prone passive knee extension exercise, laying down on the belly, with knees over the bench (unsupported leg).[rx]
- Straight leg raises[rx]
- Leg presses[rx]
- Also mini-squats, a walking program, the use of a recumbent or stationary bicycle, a swimming program, or possibly an elliptical machine are the most successful rehabilitation programs.[rx]
Rehabilitation programs will have the greatest success when focussing on strengthening the quadriceps muscles which are directly attached to the medial plica, and when avoiding activities that cause medial plica irritation.[rx]
The most important part of the quadriceps to train is the m. vastus mediale. Full range of quadriceps training is not recommended because these create excessive patellar compression at 90°. Instead, straight leg raises and short-arc quadriceps exercises at 5°-10°, also hip adductor strengthening should be performed. Other exercises to be performed are squad, go up and down the stairs, and lunging forward.[rx]. Other important components of this treatment are a stretching program for these muscles(quadriceps, hamstrings, and gastrocnemius) and knee extension exercises. The goal of these knee extension exercises is the strengthening of the tensor musculature of the joint capsule. But if the patient has too much pain when reaching terminal extension, then this should be avoided[rx]. This conservative treatment is effective in most cases, but in some patients surgery is necessary. In this case, post-operative therapy is necessary. The postoperative treatment is identical to the conservative treatment and is usually started 15 days after the surgery. The main goal of physiotherapy in plica syndrome is to reduce pain, maximize the ROM, and increase the strength of the muscles.
The type of plica, the age of the patient, and the duration of symptoms will greatly influence the success rate of conservative non-operative treatment of plica syndrome. It is generally believed that infrapatellar and lateral plica syndrome is not very responsive to physical therapy and will normally require surgery. The success of conservative therapy is also more likely in younger patients with only a short duration of symptoms, as the plica will not yet have undergone morphological changes. In general, the overall success of the non-surgical treatment is relatively low and complete relief of symptoms is only rarely achieved.
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