Knee pain and swelling can be caused by injury, arthritis, bursitis, ligament injuries, torn cartilage, Baker’s cyst, autoimmune diseases, blood clots, or cancer. Rest and home care can help, but seeing a doctor is recommended. Different forms of arthritis, Osgood-Schlatter disease, and Baker’s cyst are also discussed.
Knee pain and swelling are often caused by a knee injury. Other causes are arthritis, bursitis, major or minor ligament injuries, torn cartilage, and Baker’s cyst. Less common causes of knee pain and swelling include autoimmune diseases such as psoriasis; in rare cases, it can be the result of a blood clot or cancer. Knowing whether the knee pain is on one side or both sides and whether it is transient or constant gives your doctor clues that point to the correct diagnosis. While a person should see a doctor whenever there is knee pain and swelling, rest and home care usually allow knee pain to resolve on its own.
The knee can be damaged by overuse, improper footwear, poor athletic form, or trips and falls. Knee injuries usually affect only one knee and often involve the anterior cruciate ligament or medial collateral ligament. These injuries can be simple strains and sprains or be severe enough to cause internal bleeding in the knee, increasing knee pain and swelling. Runners or skiers can develop tendonitis, an inflammation of the tendons around the knee. Excessive knee twisting or flexion can cause a meniscal tear, while a popping sensation may occur at the time of the injury, and the knee joint will lock repeatedly with pain and swelling.
In athletic adolescents, repeated small injuries can cause pain and swelling around the knee. This condition is called Osgood-Schlatter disease and is most often seen in boys aged 10 to 15 who play sports. Bursitis, or maid’s knee, results from a period of excessive pressure on the knees and occurs in jobs that require kneeling, such as carpet layers, cleaners, or tile layers. Occasionally, knee injuries require surgery, although an injured knee often resolves with rest and treatment such as acetaminophen or ibuprofen.
Different forms of arthritis can cause pain and swelling in the knee. Rheumatoid arthritis is an autoimmune disease that can affect any joint in the body and often multiple joints are affected at the same time. Osteoarthritis occurs from a lifetime of wear and tear and is common as we age. Gout is a form of arthritis that results from the buildup of uric acid crystals in the joints. Pseudogout is similar, except that calcium pyrophosphate crystals form in the joint fluid; the most common joint affected by pseudogout is the knee.
A swelling behind the knee that looks like a water balloon could be a Baker’s cyst. This cyst forms from an excess of synovial fluid, the fluid that lubricates the knee. It can be painful with swelling or it can be painless with no other symptoms. Baker’s cysts can accompany arthritis and injuries such as meniscus tears.
Autoimmune diseases that cause widespread systemic inflammation can also lead to knee pain and swelling. Psoriasis is a disease in which the skin develops red, itchy, scaly patches. Patients with psoriasis can also develop psoriatic arthritis affecting both knees. Lupus and Crohn’s disease can also cause swollen and painful knees.
Less commonly, knee pain and swelling can indicate a serious condition. Knee pain can be a symptom of a blood clot in the leg or deep vein thrombosis. Knee joint infection is usually accompanied by pain, swelling, and fever. Bone tumors can also present as pain and swelling in the knee.
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