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A Rare Case of Synovial Osteochondromastosis Outside the Ankle Joint

Two podiatrists from the University of North Texas Health Science Center offer this case study of a rare ankle problem: extrasynovial synovial osteochondromatosis. Hootchy-what, you say? Let's break that down a bit -- extrasynovial means the problem has to do with synovial fluid being outside of a joint. Synovium is the fluid that keeps the joints lubricated and moving smoothly. It is a viscous (slippery) membrane that lines the cartilage (cartilage covers the bone).

Normally, the synovial fluid stays inside the joint. Any synovial fluid outside the joint is considered extrasynovial. We'll come back to the significance of that in a moment. Now for osteochondromatosis: osteo refers to bone, chondro is the cartilage, and osis at the end of a word just tells us something is wrong. In this case, the synovium has started to proliferate or grow too much.

It clumps together with the cartilage forming small nodules that eventually harden. These tiny osteocartilaginous (bone and cartilage) bodies can stick to the synovium inside the joint. They can also move outside of the joint and become loose bodies floating around the various bones that form the ankle joint.

Sometimes the body breaks down and absorbs these tiny masses. In other cases, they get stuck between two bones or embedded in a tendon. The clinical picture is one of pain, loss of motion, and a joint that locks up with movement. In this case report, a 56-year-old woman had injured her left ankle and then noticed over time a bump growing along the anteromedial (front and inside) aspect of her ankle.

She eventually went to see the podiatrist (the authors of this case report). A patient history, physical exam, X-rays, and MRIs led to a diagnosis of chronic calcific ganglion. A ganglion is a cyst. A calcific ganglion means it has hardened. Surgery to remove the mass was followed by examination of the tissue in the pathology lab. It wasn't until the pathologist analyzed the mass that the final diagnosis of extrasynovial synovial osteochondromatosis was made.

It wasn't a ganglion cyst after all. The pathologist confirmed it was a combination of bone and cartilage. The surgeon found the hard mass outside of the ankle joint. It was free from any tendons nearby, which made it easier to remove. The patient was reevaluated nine months after surgery. She had no symptoms and there was no sign that the mass was coming back.

In this case, it can be said that All's well that ends well. But the authors note that sometimes these osteochondral masses can grow back. They can even become malignant. That only happens about five per cent of the time but it's something to watch out for. No one knows why this transformation from benign mass to malignant tumor (chondrosarcoma) occurs. There isn't a way to predict who might develop a malignancy. That's why the masses are removed and then observed closely afterwards.

Since synovial osteochondromatosis outside the synovium is such a rare condition, the authors felt it was important to publish their experience and observations with this case. Others may benefit from knowing that even with X-rays and MRIs, the final diagnosis isn't always known until the tissue has been removed and examined by a pathologist. Because of the risk of malignancy, follow-up is very important.


Brian Carpenter, DPM, FACFAS, and John Clyde, DPM. Extrasynovial Synovial Osteochondromatosis of the Ankle: A Case Report. In The Foot and Ankle Online Journal. June 2010. Vol. 3. No. 6.

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*Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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