Plica are common anatomical structures found within certain joints of the body. These natural folds of tissue can exist without causing any issues, often going unnoticed throughout a person’s life. However, understanding plica is important for recognizing when these structures might become a source of discomfort or pain.
Understanding Plica
Plica are folds in the synovial membrane, the thin lining that surrounds and lubricates joints. These folds are remnants from early human development, specifically during joint formation in the womb. For example, the knee joint is initially divided into three separate compartments by mesenchymal tissue that usually resorbs by the 16th week of gestation.
However, in many individuals, this resorption is not complete, leaving behind these folds of synovial tissue. Plica are considered vestigial structures, meaning they are remnants of evolutionary or developmental processes that no longer serve a primary function. While plica can be found in various joints, they are most frequently observed in the knee, where they are present in approximately 50% of the population.
In the knee, four types of plica are commonly distinguished based on their anatomical location: suprapatellar, infrapatellar, medial patellar, and lateral patellar plica. The infrapatellar plica, also known as the ligamentum mucosum, is the most common type in the knee. However, the medial patellar plica, located on the inner side of the knee, is most frequently implicated in symptomatic conditions due to its anatomical position.
Causes and Symptoms of Plica Syndrome
While plica are a normal part of joint anatomy, they can become problematic, leading to plica syndrome. This occurs when a plica becomes irritated, inflamed, or enlarged. The inflammation is typically caused by the plica being pinched between bones, such as the femur and patella in the knee, or by friction from repetitive movements.
Common causes of this irritation include overuse from repetitive activities like bending and straightening the knee, such as running, cycling, or using a stair-climbing machine. Direct trauma to the knee, like a fall or impact, can also inflame the plica and the surrounding synovial tissue. Over time, repeated irritation can cause the plica to thicken and develop fibrosis.
Symptomatic plica often cause specific symptoms, primarily pain typically located in the front or inner side of the knee. This pain may worsen with activities that stress the patellofemoral joint, such as climbing stairs, squatting, or standing up from a chair after prolonged sitting. Other common symptoms include clicking, popping, or snapping sensations when bending or extending the knee. Some individuals may also experience localized swelling, a catching sensation, or a feeling of instability in the knee. In some cases, the irritated plica may even be felt as a tender band under the skin.
Identifying and Treating Plica Syndrome
Medical professionals diagnose plica syndrome through a comprehensive evaluation, beginning with a physical examination and a detailed history of symptoms. During the physical exam, the doctor may palpate the knee to feel for a tender, ribbon-like fold of tissue. Specific physical tests, such as the Stutter test or Hughston test, can also help indicate plica syndrome.
Imaging techniques like X-rays are generally not diagnostic for plica syndrome, but they can be useful for ruling out other conditions with similar symptoms, such as tendinitis, meniscal tears, or bone injuries. Magnetic resonance imaging (MRI) may show hypertrophy or inflammation of the plica, but it is not always definitive and is often used to exclude other pathologies. The diagnosis is often made by exclusion, meaning other potential causes of knee pain are ruled out first.
Initial treatment for plica syndrome typically involves conservative measures to reduce pain and inflammation. Rest and activity modification, such as avoiding repetitive knee movements that aggravate symptoms, are often recommended. Ice therapy applied several times a day helps reduce inflammation. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen are commonly prescribed to alleviate pain and swelling.
Physical therapy is a cornerstone of conservative treatment, focusing on strengthening quadriceps muscles, stretching hamstrings, and improving overall knee stability. In some cases, corticosteroid injections into the plica may be considered for temporary relief, especially in younger patients with recent symptoms. If conservative treatments, typically tried for at least six to eight weeks, do not provide sufficient relief, surgical options may be explored. Arthroscopic plica excision is a minimally invasive procedure where the inflamed plica is removed using small incisions and specialized instruments.