A plica is a normal anatomical structure, best described as a fold of tissue made from the joint’s inner lining, the synovial membrane. This membrane encloses the joint space and produces synovial fluid, which lubricates the joint surfaces. Plicae are remnants of the knee’s embryonic development, where the joint was initially divided into compartments by these folds. Although they usually disappear before birth, they persist in most people as soft, flexible folds within the joint capsule. In its normal state, a plica is generally asymptomatic.
Anatomical Location and Types
While plicae are found in various parts of the body, their clinical relevance is most commonly associated with the knee joint. In the knee, four distinct types of synovial plicae are described, categorized by their location around the patella (kneecap). These include the Suprapatellar, Mediopatellar, Infrapatellar, and Lateral plicae.
The Suprapatellar plica lies between the suprapatellar bursa and the main knee joint cavity. The Infrapatellar plica, also known as the ligamentum mucosum, is situated below the kneecap. The Lateral plica, found on the outer side of the knee, is the rarest type. The Mediopatellar plica, which runs along the inner side of the joint, is the one most frequently associated with causing symptoms and is often called the medial shelf.
The Infrapatellar and Suprapatellar plicae are the most common types found in knees. However, the Mediopatellar plica is the one most likely to become irritated. This specific plica extends from the medial wall of the knee joint and can rub against the medial femoral condyle (the inner end of the thigh bone).
Plica Syndrome Causes and Symptoms
Plica Syndrome occurs when a normal, soft plica becomes inflamed, thickened, and less pliable, causing it to become symptomatic. This change in tissue texture leads to the plica catching or rubbing abnormally over the joint surfaces, particularly the medial femoral condyle, during knee movement. The primary causes for this irritation are acute trauma, such as a direct blow to the knee, or chronic repetitive stress.
Repetitive activities involving frequent bending and straightening of the knee, like running or cycling, can lead to chronic irritation and inflammation. When the plica becomes thick and fibrotic, it loses elasticity and can be pinched between the kneecap and the thigh bone. This mechanical impingement causes the symptoms associated with the syndrome.
The most common complaint is persistent pain located in the anterior and medial aspect of the knee. This discomfort is often described as a dull, aching sensation that worsens with activities that load the patellofemoral joint, such as squatting, kneeling, or climbing stairs. A distinguishing symptom is an audible clicking, popping, or snapping sensation that occurs during knee movement, typically between 30 and 60 degrees of flexion.
Patients may also report a catching or locking sensation, or a feeling of instability, especially when rising after sitting for a long time. On physical examination, the irritated plica may be tender to the touch and sometimes palpable as a taut, painful band along the medial border of the kneecap. These mechanical symptoms help distinguish Plica Syndrome from more generalized knee pain.
Diagnosis and Treatment Approaches
Diagnosing Plica Syndrome relies heavily on a thorough clinical assessment, as its symptoms often overlap with other common knee conditions like meniscus tears or patellofemoral pain. A healthcare provider will take a detailed patient history and perform a physical examination to check for localized tenderness and to elicit the characteristic clicking or snapping sensation. Specific maneuvers, such as the Plica Stutter Test, which involves resisting knee extension while the plica is palpated, can suggest the diagnosis.
Imaging techniques like X-rays are usually normal in Plica Syndrome, but they may be used to rule out bony abnormalities. Magnetic Resonance Imaging (MRI) is often utilized to exclude other potential causes of knee pain, such as ligament or meniscal injuries. While a symptomatic plica may appear thickened on an MRI, the diagnosis remains primarily clinical because the plica itself can be difficult to visualize clearly.
The initial treatment for Plica Syndrome is non-surgical and aims to reduce inflammation and irritation. This conservative management includes a period of rest and avoiding activities that aggravate the symptoms. Non-steroidal anti-inflammatory drugs (NSAIDs) are often prescribed to help decrease swelling and discomfort.
Physical therapy is a major component of non-surgical care, focusing on stretching tight muscles, such as the hamstrings, and strengthening the quadriceps to improve overall knee mechanics. For cases that do not respond to this initial approach, a corticosteroid injection directly into the inflamed plica may be considered for potent anti-inflammatory relief. If non-surgical treatment fails to relieve symptoms after several months, the condition may require arthroscopic surgery. This minimally invasive procedure involves removing the irritated plica tissue, resolving the mechanical impingement within the joint.