Loose body. Rice body. Joint mouse.
These odd-sounding words are all common names for a reasonably common knee problem. The official term is corpus liberum – literally, free body. (And, yes, some people really do call them joint mice.)
What is a loose body? Put simply, it’s a fragment of cartilage or bone that breaks away from the joint surface – usually because of an injury or through long-term wear-and-tear.
Once detached, the fragment can remain trapped in the joint: this is known as a “stable” body. Or it can break off and move through the synovial fluid in the joint: an “unstable” fragment.
Either way, a loose body has the potential to cause problems for the knee. So, if you develop one, what can you do about it? Here are some of potential options…
How painful is a loose body in the knee?
It varies. Loose bodies can be asymptomatic – i.e., you won’t even know you have one. Over time, however, they often start to cause irritation or moderate to significant pain. Unstable loose bodies can also cause mechanical problems. The fragment can slip into the space between bones, causing the knee to catch or lock and making it hard to flex the leg or even walk. You could also see swelling as the fragment begins to irritate the tissues.
What size is a loose body in the knee?
Again, it varies. Some are microscopic. Others can calcify and grow much larger – even to the size of a golf ball. A condition called synovial chondromatosis can lead to hundreds or even thousands of tiny fragments. Here in the clinic, however, most of the loose bodies we see tend to be about 5-10mm wide. Most patients have between one to four fragments in their knee.
How do you treat a loose body in the knee?
Loose bodies don’t always require treatment. Sometimes they simply settle and don’t cause further irritation. When they do cause issues, there are two main approaches to tackling them:
Conservative – it’s sometimes possible to treat the loose bodies with anti-inflammatories and physiotherapy to reduce inflammation and restore range of movement
Arthroscopic – more often, it’s better to remove the fragments with a simple arthroscopy operation (keyhole surgery)
How does keyhole surgery for loose bodies work?
Most loose bodies occur in front of, or just above, the kneecap. The surgeon makes two small (usually less than a centimetre) cuts below the kneecap. One is for a camera probe, which gives a close-up view of the fragments. The other cut is for the instruments, such as miniature forceps to grasp the bodies and remove them. In rarer cases where the fragments move to the back of the knee, it may be necessary to make a posteromedial or posterolateral incision (a cut to the rear and side of the knee) to access them. During the procedure the surgeon can also “tidy up” the joint, for instance by smoothing the surfaces (debridement) or trimming away small meniscal tears.
How long does it take to recover from loose body surgery?
Keyhole surgery is a minimally invasive operation, so the recovery time is usually quite fast and straightforward. It takes about two weeks for the incisions to heal, and most patients can get back to everyday activities around two weeks after that.
To operate or not to operate…
When loose bodies cause pain or mechanical issues, it’s generally best to remove them. The operation is usually simple, quick and effective. But surgery isn’t the best answer in every case. For example, if someone has extensive cartilage damage in their knee from arthritis, removing one or two tiny loose fragments may not substantially improve the situation. In these cases, it may be better to tackle the underlying arthritis problem, and perhaps even to consider a knee replacement operation. So it’s important to get a thorough diagnosis and assessment, then talk about the range of potential options for treatment.
Interested in reading more about these knee issues? You may find these articles helpful
What happens if you damage your knee cartilage? (blog)
