The knee joint functions primarily as a hinge, allowing for bending and straightening movements. The interior is lined by the synovium, a thin membrane that creates fluid to lubricate the joint. Synovial folds, known as plicae, are common anatomical structures, remnants of the partitions that divided the knee during fetal development. Medial Plica Syndrome (MPS) occurs when one of these folds, specifically the medial plica, becomes inflamed, thickened, and symptomatic.
Understanding the Medial Plica
Plicae are folds of synovial tissue that line the knee joint and are present in a large percentage of the population without causing issues. The medial plica most frequently causes symptoms due to its specific location and orientation. It runs along the inner side of the kneecap (patella), extending across the medial femoral condyle.
In most individuals, this fold is thin and flexible. However, the plica can be naturally thicker or more fibrous, sometimes described as a shelf-like structure. This variation makes the tissue susceptible to friction or catching against the femur bone during knee movement. When irritated, this tissue leads to Medial Plica Syndrome.
Identifying the Symptoms
Medial Plica Syndrome typically causes pain on the anteromedial aspect of the knee (the front and inner side), often just above the joint line. The initial pain is frequently described as a dull, persistent ache that intensifies with activity. This discomfort is noticeable during actions involving repetitive bending and straightening of the knee.
A primary sign is a mechanical sensation, such as clicking, snapping, or popping, that occurs as the knee flexes. This snapping is often felt when the knee is bent between 30 and 60 degrees, as the thickened plica catches on the femur. Patients may also experience tenderness when pressure is applied to the inner side of the kneecap. The knee may feel unstable or give way unexpectedly, and pain typically worsens during activities like climbing stairs, squatting, or sitting for long periods.
Causes of Irritation
The syndrome begins when the plica becomes inflamed and thickened. The most common trigger is repetitive stress from activities involving frequent knee flexion and extension. Sports such as running, cycling, or using a stair-climbing machine are often associated with the onset of symptoms due to the continuous rubbing of the plica against the femur.
Direct trauma, such as a blow to the knee, can also cause the plica to become acutely inflamed. Once irritated, the plica swells and thickens, which increases the likelihood of it being pinched or catching during movement. This cycle of friction, inflammation, and thickening causes the chronic pain and mechanical symptoms characteristic of the syndrome. Muscular imbalances, such as weakness in the quadriceps or tightness in the hamstrings, can also contribute by altering the mechanics of the kneecap and increasing tension on the plica.
Diagnosis and Treatment Options
Diagnosis is primarily a clinical process, relying on a physical examination and the patient’s history of symptoms. Since the plica is soft tissue, it does not appear on standard X-rays, though imaging is used to rule out other causes of knee pain, such as fractures or arthritis. Clinicians perform provocation tests, moving the knee while applying pressure to the medial side of the kneecap to reproduce the characteristic pain or snapping.
An MRI or ultrasound may be utilized to confirm the presence of a thickened plica, but these scans are primarily useful for excluding other internal knee conditions like meniscal tears or cartilage damage. The initial treatment approach is overwhelmingly conservative and non-surgical. This typically begins with rest and activity modification to reduce repetitive stress. Non-steroidal anti-inflammatory drugs (NSAIDs) and ice application manage pain and reduce inflammation.
Physical therapy is a cornerstone of conservative management, focusing on strengthening the muscles that support the knee, particularly the quadriceps and hamstrings, to improve stability and tracking. If symptoms persist after several weeks, a corticosteroid injection directly into the inflamed plica may be considered to reduce swelling and pain. Most individuals experience significant relief and a full return to activity with these non-operative measures.
If conservative treatment fails after an adequate trial (usually three to six months), surgical intervention may be recommended. The procedure of choice is an arthroscopic plica resection, or plicectomy, which is a minimally invasive, keyhole surgery. During this procedure, the surgeon uses a small camera and instruments to remove the thickened, symptomatic plica tissue. Recovery involves physical therapy to restore strength and range of motion, with a full return to activity expected within six to twelve weeks.