Knee Plica Syndrome: Causes, Symptoms, and Treatment

Knee plica syndrome (or shelf syndrome) occurs after overuse, muscle imbalance, or injury to the knee.

It is caused by inflammation and swelling of the mucosal folds (synovial folds, plicae) in the knee joint. This can lead to pain and restricted movement in the knee joint.

Three mucous membrane folds of the knee can be affected: the suprapatellar plica, the mediopatellar plica, and the infrapatellar plica. However, the mediopatellar plica is by far the most frequently affected.

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What are the causes of knee plica syndrome?

The knee joint, like all joints, is lined by a thin, smooth mucous membrane (synovial membrane).

The synovial membrane produces the synovial fluid (synovia), which reduces friction in the joint and supplies the joint cartilage with nutrients.

During embryonic development, this synovial skin forms a membrane (layer) that divides the knee joint into two separate areas.

Typically, this membrane is formed at the end of child development, so that there is greater freedom of movement in the knee joint.

However, in about 50 – 70 % of adults, a mucosal fold (plica) remains. This is usually located below, above, or inside (medial) the patella.

Many people with a plica have no problems at all. However, if the plica is more protruding (more prominent), irritation and inflammation/ knee plica syndrome may occur. Above all, overstraining the knee joint leads to irritation of the plica and, thus, to the so-called knee plica syndrome.

Stressful activities in which the knee is often bent and then stretched again (e.g., when jogging, cycling, aerobics, ball sports, etc.) are the most common causes.

Other causes of knee plica syndrome are injuries (traumas), self:

  • repetitive microtraumas
  • an instability in the knee joint
  • a muscular imbalance in the knee
  • an inflammation of the inner joint skin (synovitis)

Concerning the injury mechanisms, those play a role that brings the inner (medial) ligament parts under increased tension or directly injure them.

A functional weakness of the internal part of the quadriceps anterior thigh muscle with a change in tension of the internal capsular ligament components may be the triggering factor.

As a result of the entrapment of the connective tissue, converted plica mediopatellaris between the thigh (femur) and the patella, dents, and pannus formation (inflammatory, vascular connective tissue) on the inner, joint-forming thigh bone or on the inner patella rim may be visible during arthroscopy.

This means that this thickening of the tissue then rubs against the cartilage within the knee joint. This can lead to damage to the joint cartilage or to joint inflammation (knee plica syndrome) with continued loading.

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Symptoms of the knee plica syndrome

Injuries (trauma), repetitive micro-trauma, instability in the knee joint, muscular imbalance in the knee, and inflammation of the synovial membrane (synovitis) cause swelling and thickening of the plica (mucosal fold).

Repeated incarcerations with inflammation and fibrotic remodeling result in a self-sustaining process associated with recurrent pain, joint effusion, movement restrictions, joint snapping, and joint blockage.

The pain in knee plica syndrome is localized on the inside and is load-dependent.

Sometimes there are blockages between the inside edge of the patella and the lower part of the thigh bone (femoral condyle) during the stretching movement. Frequently a rubbing or snapping at the inner patella rim is felt. The increasingly connective tissue remodeled (fibrosis) plica mediopatellaris is often palpated as a painful strand. Sometimes there is a cracking of the joint in a particular position during joint flexion.

Depending on how severely the knee plica syndrome has already progressed, a distinction is also made between the complaints that are triggered by it.

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Stages

At the beginning of the disease, there is usually pain in the area of the knee, depending on the load. Movements often trigger complaints, which are above all very stressful for the knee and muscles. Movements such as climbing stairs, cycling, or jogging should be mentioned here. Swimming, on the other hand, is considered a gentle form of exercise. In addition to sports activities, prolonged standing and uneven loading of the knee joint are described as aggravating the symptoms.

Advanced Knee Plica Syndrome

As the disease progresses and the degree of inflammation increases, there is an influx of inflammatory fluid into the knee joint. This can then lead to swelling in the knee, which in turn leads to a reduction in space in the joint. The tightness, in turn, leads to tension pains, which the patient can experience in addition to the symptoms of the knee plica syndrome. The swelling in the knee joint can also lead to the knee no longer being able to bend or stretch in the usual way. In the case of severe swelling, the kneecap can be lifted off the knee by the effusion and thus become clearly palpable. Sometimes there may also be signs of a so-called “dancing patella.” This is a kneecap lifted off by fluid, which appears to float above the knee joint and can be pushed to the side with slight springiness by applying slight pressure.

If a knee plica syndrome persists for a long time and has not been treated, the inflammatory reactions of the body intensify. While initially only heavy loads led to the complaints in the knee, now even relatively light movements cause the complaints. The reason for this is that the inflammation in the knee joint can no longer be cured and reduced by resting, a specific residual inflammation always remains in the knee, even if no heavy load is placed on the knee.

The symptoms also increase in intensity. Thus, the pain arising in the knee joint is described as much more biting and pulling than in the case of an incipient knee plica syndrome. Effusions can also occur earlier and build up more quickly. A redness can rarely be seen in a pronounced knee plica syndrome.

In addition to the pain and impaired movement, sufferers often describe an audible cracking sound that occurs when the stretched leg is brought into a bent position or vice versa. The cause is probably a sudden, jerky drop of the condyles in the knee joint. This is also a sign of a beginning instability in the knee joint. Corresponding pain caused by an incipient but also advanced knee plica syndrome also causes patients to adopt a relieving posture during regular movements in the knee joint in order to reduce the corresponding pain. This relieving posture also inevitably leads to incorrect loading of the knee joint. The knee is no longer loaded in the usual way. Acutely, incorrect loading leads to further pain, which the patient additionally perceives. In the long run, however, such incorrect loads lead to arthroses of the upper and lower leg, but also of the pelvis. As a rule, however, therapy is initiated when the knee plica syndrome progresses.

Pronounced knee plica syndrome

If a knee plica syndrome is very pronounced or has been developing for a long time, pain at rest can also occur without appropriate movement having been exercised. At this point at the latest, all patients should consult their doctor, as failure to treat the condition would lead to an increasing loss of movement.

The trapped plica can usually be mobilized again with appropriate movement, which then reduces the pain peak accordingly. Sometimes, however, it can also happen that this incarceration cannot be released by movement and remains. At rest or during movement, this leads to severe to very severe pain. Patients usually try to find the most bearable position for themselves by making the slightest movement in the knee joint and are usually very painful. Even with this relatively rare course of a knee plica syndrome, rapid action is required to prevent irreparable damage to the knee joint.

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Diagnosis

In order to diagnose a knee plica syndrome, one first tries to localize the pain accurately or to determine an occurred thickening in the area of the patella.

Often one can also feel the rubbing of the plica in the knee joint when moving.

The soles sign is positive. In the case of the single sign, the upper edge of the patella is grasped with thumb and index finger, and the patella is pushed down. If the four-headed front thigh muscle (M. quadriceps) is now tensed, the patella is pressed onto the lower parts of the thigh bone (femoral condyles), which is felt as painful if the cartilage is damaged.

50% of all patients generally find it very unpleasant to perform this test on them.

Overall, the knee plica syndrome is not easy to diagnose because the overlapping of other pathological lesions (rupture of the cruciate ligament, meniscus damage, etc.) makes the diagnosis more difficult.

A magnetic resonance examination (imaging procedure) can also help make a diagnosis. However, it does not always have to provide precise results.

In some patients, knee plica syndrome is only definitively confirmed by arthroscopy of the knee joint. It follows that the exact clarification is almost only possible by arthroscopy. On the other hand, the diagnosis of knee plica syndrome is often a diagnosis of embarrassment when no other pathological changes in the knee joint that explain the symptoms can be detected in the case of recurring complaints in the knee joint.

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Therapy of the knee plica syndrome

Once a knee plica syndrome has been diagnosed, the severity of the disease is first assessed, after which the treatment strategy is determined. In general, a distinction is made between conservative and operative therapy.

The knee plica syndrome is initially treated conservatively.

It is carried out with local and oral anti-inflammatory drugs (antiphlogistics).

Conservative therapy also includes rest, physiotherapy with connective tissue massages, and training of the often strength-reduced middle part of the four-headed front thigh muscle (Musculus vastus medialis).

Cooling with ice is also helpful and relieves pain and swelling. The local administration of anti-inflammatory injections (steroid injection) is questionable about its effect in the treatment of knee plica syndrome.

The problem with knee plica syndrome, however, when it occurs in athletic patients, is that the symptoms usually do not get better because the inflammatory changed and hardened edge of the plica continues to rub against the cartilage, destroying it.

For this reason, knee endoscopy (arthroscopy) should be considered at an early stage in sports patients.

Otherwise, arthroscopy is indicated if the symptoms do not disappear with conservative therapy. In arthroscopy, the plica is removed (resected).

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Conservative therapy

All therapeutic instruments that are not operative are used.

The first important thing is to protect the affected knee. Sporting overloading should be avoided altogether. Stress on the knee during jogging or hiking in the mountains should also be avoided if possible. Swimming and other joint-gentle measures are highly recommended. However, the leg should by no means be held in a resting position, as this is not good for the joint and also increases the risk of deep vein thrombosis.

In addition to reducing the overloading, pain-relieving measures should be taken. Physical pain treatment should be mentioned. This includes regular treatment with ice packs, which should be placed on the knee. Physiotherapeutic measures can also be taken to relieve the knee joint as much as possible using appropriate exercises to build up the muscles around the knee. Physiotherapy should be carried out regularly, and care should be taken to avoid overloading the muscles.

It can also be helpful to stabilize the knee during everyday movements (such as running, bending, and stretching). The use of a bandage can be useful and helpful for this. However, the knee should still be freely movable and not be too compressed. If the bandage increases the pain, the bandage should be loosened or wholly omitted.

The conservative treatment of a knee plica syndrome also includes pain treatment with medication. It makes sense to combine a drug that has both pain-relieving and anti-inflammatory effects.

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Surgical therapy of the knee plica syndrome

If the symptoms do not improve under conservative treatment, it must be considered whether an operation leads to the desired success. Today, the operation is performed minimally invasively and is also known as arthroscopic surgery. It can be performed under general anesthesia or by blocking the nerves of the corresponding leg.

The patient is first informed about the risks of the operation. These include bleeding that is difficult to stop, infection of the joint, wound healing disorders, allergic reactions to the anesthetic, or the need to operate on the knee open due to anatomical conditions.

After the patient has given consent for the operation, and an appropriate anesthetic has been administered, the knee is washed with a sterile liquid. Two small skin incisions around the knee joint serve as entry points for two rod-shaped instruments which are inserted into the knee joint. One is a camera with a bright light, and the other is an inlet for liquid. Also, it can also be used to insert instruments into the knee joint, which are necessary for smoothing cartilage and for cutting and suturing.

After the instruments have been inserted, a diagnostic view of the knee joint begins. The camera delivers images in real-time, which can also be recorded for documentation purposes. During the operation, the knee is regularly bent and stretched to see whether parts of the knee become trapped during movement and thus cause pain. Once the examiner has located the plica, he or she will begin with the ablation. In addition, an inserted smoothing instrument can be used to remove excess and disturbing cartilage. Sterile fluid is then pumped into the knee joint through the water inlet and immediately sucked out again. This also rinses the crushed parts of the plica out of the knee joint.

Shortly before the end of the operation, small sutures are inserted, and the joint skin is closed. Since this area is well supplied with blood vessels, it may often be necessary to stop bleeding using electrocoagulation. After removing the instruments, the skin incisions are sutured and sterilely connected. The sutures can then be removed approx 10-12 days after the procedure.

Often the treatment of a knee plica syndrome (also known as plica- syndrome, plica-knee plica syndrome) is conservative. Anti-inflammatory measures are used to try to reduce the painful conditions of a knee plica syndrome. Furthermore, a treatment approach through physiotherapy is often attempted.

If there is no improvement in the symptoms, a surgical procedure should be considered.

The surgical procedure can either be performed under general anesthesia or by a nerve block where the patient is conscious but does not feel pain during the procedure on the knee.

In the past, such operations were performed exclusively on the open knee. Today, the minimally invasive procedure is mainly chosen, which is also known as arthroscopy.

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Arthroscopy of the knee

The knee endoscopy is seen on the one hand as a diagnostic measure and, on the other hand, as a therapeutic measure. If imaging procedures such as magnetic resonance imaging of the knee can provide a reasonably reliable diagnosis in cases where knee plica syndrome is suspected, then a knee joint mirror image can provide definitive proof.

During arthroscopy, two small skin incisions are made on the previously disinfected knee joint, through which an instrument with a camera is then inserted. Through the other skin incision, another instrument is pushed, which has an irrigation device, but also an inlet that allows other instruments, such as sutures and forceps, to be introduced into the knee joint.

The knee is brought to a 90-degree angle before the operation on a lying patient. The two instruments are then inserted into the joint gap through the skin incisions made. With the help of the camera and the bright light source attached to it, the knee can then be inspected and the position of the ligaments and cartilage, as well as the space conditions, can be assessed. Sterile fluid can be pumped into the knee joint with the aid of the irrigation device and then sucked out again. The cartilage that protrudes into the joint space can be smoothed and removed with an additionally inserted instrument.

During the examination, it is essential not to keep the knee in a static position but to move it back and forth on the lying patient by bending and stretching it. This is the only way to ensure that the examination can also see the corresponding space conditions during normal knee movement. During this maneuver, in the case of a knee plica syndrome, it is also possible to see whether a plica is located in the area of the knee joint in an extended manner. During the entire procedure, the camera can be used to take pictures and video recordings for documentation purposes. Once this procedure has reliably diagnosed a knee plica syndrome, the diagnostic procedure is completed, and the therapeutic procedure begins.

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The plica is then removed piece by piece. For this purpose, a so-called burr is now inserted through a skin incision into the knee joint. This removes the inner skin of the knee in the area that is fibrotic, and inflammatory processes become visible. The ablation takes place in this area down to the capsule. The removed material can be removed from the knee using small forceps and suction devices.

In contrast to the menisci, the joint skin is well interspersed with blood vessels. Partly for this reason, moderate to heavy bleeding may occur during the procedure, which then has to be stopped by a so-called electrocoagulation or injection. For this reason, it is crucial to clarify in advance whether the patient is taking blood-thinning medication such as ASA or Marcumar. These must then be discontinued accordingly before such an operation.

After appropriate sutures have been applied to the knee, the instruments are removed from the knee, and the open wound at the knee joint is closed with a skin suture. After the skin wounds have been sterilely dressed, the patient is transferred from the operating theatre to the regular ward. The procedure takes between 20 minutes and one hour. In sporadic cases, it may be necessary to continue the operation, which was initially started arthroscopically, open. This is particularly necessary if anatomical conditions in the knee joint do not allow an adequate view through an arthroscopy or if severe bleeding that occurs during surgery cannot be stopped arthroscopically.

The operation is one of the routine procedures in orthopedics. However, complications can also occur here. In addition to unstoppable bleeding during the operation, wound healing disorders and infections in the wound area can also occur after skin closure. In rare cases, infections of the knee joint can also occur despite very sterile work. This very dreaded complication must be treated immediately with antibiotics. If no corresponding effect can be achieved, the knee may have to be reopened surgically. Here, in addition to sterile irrigations, local antibiotic measures (e.g., insertion of antibiotic-coated chains) would then be possible.

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Prognosis

After arthroscopy, the symptoms usually improve after a short time, unless there is already significant cartilage damage.

In this case, there is no complete improvement even after the removal of the plica.

Summary

Knee plica syndrome is caused by a thickening of a fold of mucous membrane in the knee. This thickening can be caused by trauma, inflammation, and muscular imbalance, i.e., unbalanced muscle tension. This causes pain, especially on the inside of the knee.

The diagnosis can often only be proven by a joint endoscopy (arthroscopy). Therapy is initially limited to conservative measures such as rest, anti-inflammatory drugs, cooling, and physiotherapy.

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