Loose Bodies in the Knee: When Something Moves Inside the Joint

What are loose bodies?

A loose body is a piece of cartilage, bone or both that has broken free and moves around in the joint fluid. Some are tiny, others the size of a pea or larger. Because they float, they can slip between the joint surfaces at unpredictable moments and jam the knee, which is why surgeons sometimes call them a joint mouse.

Loose bodies are not dangerous in themselves, but they can scratch the cartilage, cause repeated swelling and, if they are pieces of a damaged joint surface, signal a problem that needs attention.

Symptoms in patients' own words

• "My knee suddenly locks and I have to wiggle it to free it"
• "I get a sharp catching pain, then it's fine again"
• "I can feel a little lump that moves around the side of my knee"
• "It swells up after it catches"
• "It gets stuck when I kneel or bend fully, like in sujood"

Symptoms often come and go, because the fragment is only a problem when it gets caught. Some loose bodies cause no symptoms at all and are found on an X-ray or scan done for another reason.

Causes and who gets them

Common sources of loose bodies include:

• Osteochondritis dissecans, where a piece of bone and cartilage separates, usually in teenagers and young adults
• Kneecap dislocation, which can knock off a fragment of cartilage and bone
• Twisting or impact injuries that break off part of the joint surface
• Osteoarthritis, where fragments of bone spurs or worn cartilage break away
• Synovial chondromatosis, an uncommon condition in which the joint lining forms many small cartilage nodules

In Qatar we see loose bodies after kneecap dislocations in football, basketball and padel, in teenage athletes with osteochondritis dissecans, and in older adults with arthritis who notice catching when sitting on the floor or getting up from prayer.

Diagnosis

Dr. Gelber asks how and when the knee locks, examines it for swelling, movement and tenderness, and checks the ligaments and kneecap. X-rays show loose bodies that contain bone, and the arthritis or bone spurs behind them. Pure cartilage fragments do not show on X-ray, so an MRI is often used to find them, see where they came from and check for other injuries such as a meniscus tear. A CT scan is sometimes helpful for planning.

A knee that locks is not always caused by a loose body. A torn meniscus, especially a bucket-handle tear, can do the same, which is why imaging matters.

Treatment

A loose body that causes no symptoms may simply be watched, especially in an arthritic knee where it is one of many findings.

A loose body that locks, catches or causes swelling usually needs removal, because it will not dissolve and physiotherapy cannot move it out of the joint. Knee arthroscopy is the standard method: a camera and small instruments are passed through tiny incisions, the fragment is found and removed, and the rest of the joint is inspected.

In a young patient with a large, fresh fragment from osteochondritis dissecans or a kneecap dislocation, it may be possible to fix the piece back in place rather than remove it, preserving the joint surface. Where cartilage has been lost, cartilage restoration may be considered. In synovial chondromatosis, the abnormal joint lining is also removed to lower the chance of recurrence. The underlying cause, such as an unstable kneecap, is treated as needed.

Recovery

After simple arthroscopic removal, most patients walk the same day, return to desk work within days to a couple of weeks, and go back to sport over several weeks with physiotherapy. If a fragment is fixed back in place, the knee needs protection while it heals, with crutches and a longer return to sport, usually a few months. Your plan depends on what is found during surgery.

When to see a specialist in Doha

See a knee specialist if your knee locks, catches repeatedly, swells after catching, or you can feel something moving inside it. A knee that is stuck and cannot straighten after an injury should be seen promptly, as early surgery may be needed. Dr. Gelber assesses locking knees at Aman Hospital in Doha.