A loose body is a free-floating piece of bone, cartilage, or a foreign object in a joint. The knee is the most common site for loose bodies.

Causes of loose bodies include:

• Degenerative joint disease (osteoarthritis).
• A chip fracture.
• A torn piece of the cartilage.
• An object, such as a dislodged piece of hardware from a previous surgery or a foreign object from a penetrating injury.
• Inflammation or decreased blood supply (avascular necrosis) to the bone and cartilage, which may cause the bone to separate from the cartilage (osteochondritis dissecans).

Symptoms of a loose body in the knee joint may include:

• Locking of the knee that comes and goes.
• Pain and swelling of the knee that comes and goes.
• Ability to feel the loose body by touching the knee.
• Ongoing (chronic) stiffness.

Your doctor may order a test, such as an X-ray, ultrasound, CT scan, or MRI, to help find a loose body. Surgery to remove the loose body or repair the kneecap may be needed if a loose body is causing symptoms.