Swelling on the outside of the knee: what to know

A bump directly over the outer side may involve an irritated bursa or another superficial tissue. Swelling that feels deep, spreads around the kneecap, or follows activity may be fluid within the joint. An ACL tear or meniscus tear can present with swelling and may also cause instability, clicking, locking, or reduced confidence on stairs. Knee osteoarthritis can cause broader swelling and stiffness, while gout may make the area hot, red, and very tender.

The exact spot matters: note whether the fullness is beside the kneecap, along the joint line, or behind the knee. Also observe whether it changes with bending, running, kneeling, or pressure.

Reduce the activity that increases the outer-knee fullness and avoid leaning or kneeling on that side. Keep the knee gently mobile without forcing painful or restricted movement. Elevate the leg when resting, and use a cloth-wrapped cold pack for short periods if the area feels irritated. Wear comfortable footwear and avoid testing the knee repeatedly.

If the swelling remains or returns, arrange an examination. The clinician may assess the joint line, ligaments, nearby tendons, and bursa; joint aspiration is considered only when a clinician believes removing or analysing fluid is useful.

Seek urgent care for a hot, red swollen knee with fever, sudden inability to bear weight, an obvious deformity, or new calf swelling and pain. Arrange prompt review after a twist if the knee locks, gives way, or swells quickly. Routine assessment is sensible when outer swelling lasts, grows, or limits walking, stairs, or bending.

Is the swelling superficial or inside the joint? Which structure sits beneath this area? Could the findings fit bursitis, a meniscus tear, an ACL tear, gout, or osteoarthritis? What movements should I pause, and would imaging or joint aspiration add useful information?