Side of My Knee Is Swollen: What It Can Mean and What to Do

A bump on the outside of the knee may involve a local bursa, tendon, or the tissues that support the joint. Swelling along the inner side can also follow irritation from repeated loading or a strain. When the whole knee feels full or tight, fluid may be collecting within the joint rather than only under the skin. A soft fullness behind the knee can be associated with a Baker's cyst.

After a twist, sudden change of direction, fall, or impact, ligament or cartilage injury may be considered. Pain with catching, locking, giving way, or difficulty fully straightening the knee gives a clinician useful clues. Warmth, marked tenderness, or a rapidly painful flare can occur with inflammatory conditions such as gout, and an examination is needed to separate these possibilities. A swollen knee is a symptom, so its presence alone does not establish a particular condition.

Reduce activities that increase the swelling, especially kneeling, running, jumping, or repeated stairs. Keep the knee moving gently within a comfortable range rather than holding it rigid for long periods. Resting the leg raised can lessen the feeling of pressure, and a wrapped cold pack may be useful for short intervals with a cloth barrier between the pack and skin. Avoid deep massage directly over a new, hot, or very tender swelling.

Arrange a clinical assessment if the swelling persists, returns, or limits walking, work, sleep, or exercise. The clinician may compare both knees, check movement and stability, and decide whether imaging or removal and testing of joint fluid is appropriate. Do not start strenuous rehabilitation until an injury has been assessed.

Seek urgent medical care for a hot, red, very painful knee with fever or feeling unwell; sudden severe swelling after an injury; inability to bear weight; a knee that looks deformed; or a foot that becomes cold, pale, numb, or weak. These features can signal an infection, significant injury, or a problem affecting circulation or nerves.

Prompt assessment is also sensible when the knee repeatedly gives way or locks, when swelling is rapidly increasing, or when pain and stiffness are worsening rather than settling. If the swelling is mild and improving after a clear strain, book routine care if it does not continue to improve or normal movement does not return.

Ask: Is the swelling inside the joint or in the tissues beside it? What examination findings point toward a bursa, ligament, meniscus, cyst, or inflammatory cause? Should I pause a particular activity, and which movements are suitable while it settles? Would an X-ray, ultrasound, MRI, or joint aspiration add useful information? What changes should prompt urgent review?