I can feel something moving around inside my knee. What could it be?

What a loose body is

A loose body is a piece of cartilage, bone or both that has broken away and floats in the joint fluid. Some people can feel it under the skin, usually above the kneecap or at the sides, and notice that it disappears and turns up somewhere else. Doctors sometimes call it a joint mouse for that reason.

It may be a single fragment or several small ones, and it can grow slowly over time because joint fluid nourishes it.

Other things it could be

• A ganglion or small cyst, which usually stays in one place
• A meniscus tear flipping in and out, which causes catching but is not felt as a lump
• A thickened plica or fat pad, felt as a fold or soft swelling at the front
• A bursa or Baker's cyst, which sits outside the joint
• Rarely, a growth of the joint lining that produces many small bodies

What you can do now

Do not try to push or massage the lump to move it, as this can irritate the joint. If the knee jams, gently bend and straighten it rather than forcing it. Ease off pivoting sports such as padel and football until it has been assessed, because repeated jamming can scratch the joint surface.

Getting it checked in Doha

Book an assessment if you feel a moving lump, or if the knee catches, locks or swells. Seek prompt care if the knee is locked and will not straighten. At Aman Hospital, Dr. Gelber examines the knee and usually starts with X-rays, which show bony fragments. An MRI shows cartilage fragments and the place they came from, which matters for treatment.