Synonyms in a broader sense
Medical: Plica syndrome, plica-shelf syndrome, medial-shelf syndrome, mediopatellar plica syndrome, plica mediopatellaris
Definition
Shelf syndrome occurs after overuse, muscle imbalance or injury to the knee. It is caused by inflammation and swelling of the mucosal folds (synovial folds, plicae) in the knee joint. This can lead to pain and restricted movement in the knee joint. Three mucous membrane folds of the knee can be affected: the suprapatellar plica, the mediopatellar plica and the infrapatellar plica. However, the mediopatellar plica is by far the most frequently affected.
What are the causes of shelf syndrome?
The knee joint, like all joints, is lined by a thin, smooth mucous membrane (synovial membrane). The synovial membrane produces the synovial fluid (synovia), which reduces friction in the joint and supplies the joint cartilage with nutrients. During embryonic development, this synovial skin forms a membrane (layer) that divides the knee joint into two separate areas.
Normally, this membrane is formed at the end of child development, so that there is greater freedom of movement in the knee joint. However, in about 50 – 70 % of adults, a mucosal fold (plica) remains. This is usually located below, above or inside (medial) the patella.
According to their localization they are referred to as plica.
- Plica infrapatellaris
- Plica suprapatellaris and
- Plica mediopatellaris
Many people with a plica have no problems at all. However, if the plica is more protruding (prominent), irritation and inflammation/shelf syndrome may occur.
Above all, overstraining the knee joint leads to irritation of the plica and thus to the so-called shelf syndrome. Stressful activities in which the knee is often bent and then stretched again (e.g. when jogging, cycling, aerobics, ball sports, etc.) are the most common causes.
Other causes of the Shelf Syndrome are injuries (trauma), self: Among the injury mechanisms, those that bring the internal (medial) ligament parts under increased tension or directly injure the ligament play a role. A functional weakness of the internal part of the quadriceps anterior thigh muscle (Musculus vastus medialis) with a change in the tension of the internal capsular ligament components may be the triggering factor. As a result of the entrapment of the connective tissue of the mediopatellar plica between the thigh (femur) and the patella, dents and pannus (inflammatory connective tissue rich in vessels) may occur on the inner side of the femur, which forms the joint, or on the inner edge of the patella.
This means that the thickened tissue then rubs against the cartilage within the knee joint. This can lead to damage to the joint cartilage or to joint inflammation (shelf syndrome) with continued stress.
- Repeated microtraumas
- An instability in the knee joint
- A muscular imbalance in the knee
- Inflammation of the synovial membrane (synovitis)
