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Knee Bone or Joint Injury

Plica Syndrome

Minute Read


Posted 1 year ago


Last updated: 29/11/2022


by James McCormack

What is the Plica?

The plica is a folded membrane that sits between the synovial membrane of the tibiofemoral joint and the synovial membrane of the patella. There are 4 plicae, each a distinct fold: suprapatellar, mediopatellar, infrapatellar and lateral plicae. The membrane when healthy is usually thin, elastic and flexible, with a good blood supply. At the top of the knee it is attached to the genu articularis muscle, and inferiorly it blends into the synovial membrane of the tibiofemoral joint. It is able to change shape as the knee is bent and straightened to match the shape of the knee and prevent it catching or becoming impinged.

The plicae are the remnant of the 3 separate compartments of the knee that are present as the foetus develops in vitro. The membrane becomes partially absorbed during foetal development, but leaves the folds. The plica is noted in surgery in almost everyone, but can be more prominent in some people, than others (Griffith & LaPrade, 2008).

Intra-articular photo of plica

What is Plica Syndrome?

In a healthy knee the plicae are flexible, elastic and thin with a good blood supply. Plica syndrome is a painful condition of the knee, where the synovial membrane has become thickened and/or fibrotic and therefore is less flexible. It therefore is less able to change shape as the knee bends and straightens and can catch or become impinged, thus becoming inflamed and painful. This can be triggered by injury, such as a sudden trauma, or overuse, or related to surgery and the resultant scarring of the plica. The most common part of the plica that is affected is the medial patella plica, this is most vulnerable when the knee is flexed between 70-100º.

What Does Plica Syndrome Feel Like?

The most common symptom of plica syndrome is pain in the knee. The location of pain will be deeper in the joint rather than superficial and may not feel clearly in one place, but can felt more on the medial or inner side of the knee. Pain can be more significant at night as the body undergoes repair processes when we sleep.  There is often diffuse swelling of the knee causes by the inflammation and joint effusion, and clicking or poppling in the knee is frequently felt when the knee is bent or straightened. It can be uncomfortable to sit for long periods of time, and squatting or climbing stairs can aggravate pain. There will often be a feeling of instability when on a slope or stairs. As these symptoms are similar to many other musculoskeletal conditions of the knee, it is thought to be an under diagnosed condition.

One of the more unique symptoms is a lump or lesion felt over the affected part of the plica. For example, with a medial patella plica inflammation, can be felt at the front of the knee in the recess between the patella and the medial joint line. Running your finger from the bottom of your knee on the inside and up, you might be able to feel a band or cord like structure in this area.

How is Plica Syndrome Diagnosed?

If plica syndrome is suspected, an examination with an experienced healthcare professional such as a physical therapist or sports doctor is recommended. They will carry out a thorough physical exam to look at your strength and flexibility, as well as to stress different structures in the knee and perform special tests. These orthopaedics tests are to see what structures are sensitive, and to see how your knee is functioning. To confirm a clinical diagnosis, diagnostic imaging such as ultrasound can be used to view the plica and assess for changes in its appearance to suggest it is inflamed, thickening or fibrosed.

Plica syndrome test

Part of the clinical assessment will include a diagnosis test specific to the plica. The medial plica syndrome test is performed with the patient lying, with their leg straight and relaxed. The area medial to the patella is palpated from the lower part of the cavity to the upper part. If a cord like structure is felt that is sensitive, and the patient report this as their symptoms, the test is concluded as positive.

What Causes Plica Syndrome?

Photo of knee trauma

Plica syndrome is common after trauma or surgery on the knee. This can be in the form of sudden or chronic overload, such as an increasing in volume or intensity of exercise, such as running, squatting or going up and down stairs a lot more. Alternatively, direct acute trauma to the knee, such as a fall onto the knee, or impact on the dashboard in a car accident are common causes of plica syndrome. Surgery is a cause of plica syndrome, as the injury to the plica during the procedure and the scarring of the plica after can cause it to thicken and become fibrosed. This makes the plica less flexible and elastic, and it can become thicker, resulting it the plica being more likely to get impinged or caught in the joint as it is moved, thus causes this inflammatory condition. After knee replacement, ACL surgery and knee arthroscopy, plica syndrome is a reported risk.

In terms of age, most cases occur between the ages of 10-30 years, evenly distributed between men and women. Genetics may play a role in the development, as it may influence the shape and depth of the folds, and the flexibility of the membrane, but there is limited evidence to confidently conclude this.

Physiotherapy with James McCormack

This is not medical advice. We recommend a consultation with a medical professional such as James McCormack. He offers Online Physiotherapy Appointments for £45.

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