Swelling on the Outer Side of the Knee

A tender spot after kneeling or repeated activity may involve a bursa or irritated tendon. A twisting injury with catching, giving way, or difficulty straightening may involve the meniscus or ACL. Stiffness that builds gradually can occur with knee osteoarthritis. Gout can produce a hot, very tender swollen joint. A Baker's cyst more often creates fullness behind the knee, although fluid may be noticed elsewhere. These patterns overlap, and the visible side does not prove the cause.

Pause activities that trigger pain, especially pivoting, running, kneeling, and deep bending. Elevate the leg when resting and apply a wrapped cold pack briefly if comfortable. Do not tightly wrap a rapidly enlarging knee or try to drain the swelling yourself. A healthcare professional can assess alignment, stability, movement, and tenderness and may recommend imaging or fluid testing.

Seek urgent medical care for fever with a hot red knee, sudden inability to stand, major injury with deformity, severe escalating pain, or numbness or color change in the foot. Book a clinical assessment for persistent swelling, recurrent episodes, locking, or a knee that repeatedly gives way.

Ask whether the swelling is inside the joint or in tissue beside it. Ask if an X-ray, scan, or joint aspiration would add useful information, which exercises are appropriate, and how to recognize a worsening problem.