Plica Syndrome: Often called “synovial plica syndrome,” this is a condition that is the result of a remnant of fetal tissue in the knee. The synovial plica are membranes that separate the knee into compartments during fetal development. These plica normally diminish in size during the second trimester of fetal development. In adults, they exist as sleeves of tissue called “synovial folds,” or plica. In some individuals, the synovial plica is more prominent and prone to irritation.
Plica is a term used to describe a fold in the lining of the knee joint. Imagine the inner lining of the knee joint as nothing more than a sleeve of tissue. This sleeve of tissue is made up of synovial tissue, a thin, slippery material that lines all joints. Just as a tailor leaves extra folds of material at the back of sleeves on a shirt to allow for unrestricted motion of the arms, the synovial sleeve of tissue has folds of material that allow movement of the bones of the joint without restriction.
Four plica synovial folds are found in the knee, but only one seems to cause trouble. This structure is called the medial plica. The medial plica attaches to the lower end of thepatella (kneecap) and runs sideways to attach to the lower end of the thighbone at the side of the knee joint closest to the other knee. Most of us (50 to 70 percent) have a medial plica, and it doesn’t cause any problems.
The primary symptom caused by plica syndrome is pain. There may also be a snapping sensation along the inside of the knee as the knee is bent. This is due to the rubbing of the thickened plica over the round edge of the thighbone where it enters the joint. This usually causes the plica to be tender to the touch. In thin people, the tissue that forms the plica may be actually be felt as a tender band underneath the skin. In rare cases where the plica has become severely irritated, the knee may become swollen.
A plica causes problems when it is irritated. This can occur over a long period of time, such as when the plica is irritated by certain exercises, repetitive motions, or kneeling. Activities that repeatedly bend and straighten the knee, such as running, biking, or use of a stair-climbing machine, can irritate the medial plica and cause plica syndrome.
Injury to the plica can also happen suddenly, such as when the knee is struck in the area around the medial plica. This can occur from a fall or even from hitting the knee on the dashboard during an automobile accident. This injury to the knee can cause the plica, and the synovial tissue around the plica, to swell and become painful. The initial injury may lead to scarring and thickening of the plica tissue later. The thickened, scarred plica fold may be more likely to cause problems later.
Diagnosis begins with a history and physical exam. The examination is used to try and determine where the pain is located and whether or not the band of tissue can be felt. X-rays will not show the plica. X-rays are mainly useful to determine if other conditions are present when there is not a clear-cut diagnosis.
If there is uncertainty in the diagnosis following the history and physical examination, or if other injuries in addition to the plica syndrome are suspected, magnetic resonance imaging(MRI) may be suggested. The MRI machine uses magnetic waves to show the soft tissues of the body. Usually this test is done to look for injuries, such as tears in the meniscus or ligaments of the knee. This test does not require any needles or special dye and is painless. A computed tomography (CT) scan may also be used to see whether the plica has become thickened. Most cases of plica syndrome will not require special tests such as the MRI or CT scan.
If the history and physical examination strongly suggest that a plica syndrome is present, then arthroscopy may be suggested to confirm the diagnosis and treat the problem at the same time. Arthroscopy is an operation that involves inserting a small fiber-optic TV camera into the knee joint, allowing the surgeon to look at the structures inside the knee joint directly. The arthroscope allows your surgeon to see the condition of the whole knee and determine whether the medial plica is inflamed.
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