Symptoms

Depending on the cause and extent of the swelling, different symptoms are observed. The knee joint can be painful and feel unstable, which is particularly noticeable when the leg is strained. Sometimes the skin may appear cracked and brittle.

If the skin barrier is not intact, this can lead to bleeding or, in the case of inflammation, to the discharge of pus. In the case of inflammatory processes, the knee appears reddened and overheated. If the swelling puts pressure on nerves or muscles, parts of the skin may feel numb and the muscles are weakened.

Mobility in the knee is often restricted. Especially bending the leg can cause pain and is then not completely possible or even completely eliminated. The timing and context of the symptoms also depends on the underlying cause: If excessive or incorrect loading triggers the symptoms, they are usually improved by immobilizing the leg.

Inflammatory processes, on the other hand, can be alleviated by light movement adapted to the pain. If pain occurs in addition to swelling, the cause is usually either trauma or an inflammatory process. Inflammatory processes particularly affect the tendon attachments of the muscles that run through the hollow of the knee (the so-called ischiocrural muscles); this is called tendinitis of the muscle in question.

The joint capsule can also be painful due to inflammatory processes. After a trauma, bones, ligaments, muscles and cartilage can be damaged and then also hurt. Often the pain is then load-dependent.

Another painful clinical picture is the Baker cyst. This is a fluid-filled sac in the joint capsule. Finally, thrombosis can also cause pain.

Swollen hollow of the knee without pain

Painless swellings of the hollow of the knee are far less common than those that cause pain.A so-called sarcoma can cause such symptoms. This is a malignant tumor, which usually develops from fat, bone or muscle cells, but is extremely rare. Another cause can be the poplietal aneurysm: this is a bulging of the popliteal artery. This can, but does not have to hurt. Water retention, which also causes painless swelling, affects the entire lower leg rather than the popliteal fossa.