What is the medial parapatellar plica, or medial plica of the knee?
The medial parapatellar plica, or medial plica of the knee, is a fold of connective tissue in the inner part of the knee joint capsule, on its inner (medial) side. The plica connects the patella to the medial side of the joint capsule and is a remnant of an embryonic blood vessel in the knee. Although everyone has a medial plica of the knee, its anatomical size – and therefore its clinical significance – varies greatly. Symptoms of the medial plica most often occur in adolescents. In symptomatic cases, the medial parapatellar plica is prominent, has a tight edge, and rubs against the femur when the knee bends, causing pain on the inner side of the knee.
How is a medial parapatellar plica, or medial plica of the knee, diagnosed?
On arrival at the paediatric orthopaedic clinic, children or adolescents complain of pain on the inner side of the knee, near the patella, related to activity. There is no clear memory of a serious injury or significant knee swelling, although many take part in sporting activities where they fall on their knees or receive minor knocks to the legs. Some adolescents describe a catching sensation in the knee. On clinical examination the knees look normal from the outside (no swelling, redness, restricted movement or signs of instability). However, tenderness is found on palpation of the knee along the inner side of the patella, and sometimes a tender thickening can be felt on palpation. Adolescents with a symptomatic medial plica usually have tighter thigh muscles. If pain occurs on firmer pressure against the femur next to the patella, and there is a catching sensation that repeats with every knee movement, an X-ray of the knee should be taken, since similar symptoms can be caused by osteochondritis dissecans (OCD) of the knee. However, the medial parapatellar plica is a soft-tissue structure and is not visible on X-ray, so the child should be referred for an MRI of the knee.
How is a medial parapatellar plica, or medial plica of the knee, treated?
A painful medial parapatellar plica, or medial plica of the knee, is best treated conservatively at first, with physical therapy. Activities that trigger pain should always be limited, and for active young athletes activities should be modified so they do not miss out on training altogether. Physical therapy includes stretching exercises for the thigh and calf muscles. Orthopaedic insoles, which ease the load on the calf muscles, are sometimes recommended and can resolve the pain around the knee. If there is no improvement after 3–4 months of conservative treatment, and an MRI clearly shows a medial parapatellar plica, surgical treatment is needed. Knee arthroscopy is performed, in which the medial parapatellar plica is divided and removed through two small portals next to the patella. After surgery, children immediately bear weight on the knee up to the point of pain and quickly return to sporting activities.
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