Bursae are small fluid-filled sacs that cushion the knee joint. If one becomes irritated from pressure, impact, or frequent kneeling, it can cause prepatellar bursitis—often called “housemaid’s knee.” This condition usually affects only one knee, leading to swelling and tenderness at the front of the joint.
3. Infection
An infection inside the knee joint (septic arthritis) is serious and demands urgent care. Symptoms often include rapid swelling, redness, warmth, and intense pain, along with fever or chills. Treatment usually involves draining infected fluid and antibiotics.
4. Gout or Pseudogout
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.
