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4. Gout or Pseudogout
Sudden, severe knee swelling might be due to a crystal-induced arthritis like gout or pseudogout. Gout happens when uric acid crystals build up in a joint, while pseudogout involves calcium crystals. Both can cause intense pain and swelling in one knee at a time, sometimes recurring in flare-ups.
5. Localized Osteoarthritis
Although osteoarthritis often affects both knees, it can start in only one—especially if there’s a history of prior injury or extra strain on that joint. Swelling from osteoarthritis tends to be mild to moderate and may worsen with physical activity.
6. Baker’s Cyst
A Baker’s cyst is a fluid-filled pocket that develops behind the knee, often linked to conditions like arthritis or cartilage tears. It can cause a feeling of tightness or visible swelling, particularly when bending or straightening the leg.
7. Blood Clot or Circulatory Problems
While less common, a blood clot (deep vein thrombosis) in the leg can cause swelling around the knee, especially if it’s accompanied by calf pain, warmth, or redness. This is a medical emergency requiring immediate attention.
When to See a Doctor
Seek medical care if:
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Swelling comes on suddenly and severely, or you develop a fever
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Your knee feels hot, red, or extremely tender
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You can’t walk, bend, or bear weight on the knee
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Swelling persists for more than a few days without getting better
Final Thoughts
Having one swollen knee isn’t always a sign of a serious problem—but it’s definitely worth investigating. From injuries to infections or joint disorders, many conditions could be responsible. Getting a proper diagnosis is the key to effective treatment and maintaining healthy knees for the long term.
