It isn't a common problem, but when a patient has an intra-articular extraskeletal osteochondroma, it's important that it be recognized and treated and not mistaken for a more serious one. Extraskeletal means not in the bone, but in the soft tissue, and osteochondroma is a benign (not cancerous) tumor that contains both soft body tissue and bone.
The authors of this article first describe a patient with this type of osteochondroma. He is a 59-year-old male how has been complaining of a dull pain and decreasing range of motion in his right knee over the past three years. He claimed to be managing well, even with his job as a heavy worker, until a mass formed behind the knee, preventing him from bending it any more than 90 degrees, a right angle.
When the doctors examined the patient, they were able to feel the mass, but it was only mildly painful. In x-rays, the only thing that could be seen that was out of the ordinary was a mass of soft tissue behind the knee. The patient also had a bit of osteoarthritis. Magnetic resonance imaging (MRI) showed the mass in more detail.
The doctor decided to excise the mass, take it out. When the tumor was biopsied, studied in the lab, it was found that the mass had bone cells and tissue in it so the diagnosis of osteochondroma was made. After six weeks, the patient returned to his regular lifestyle and he remained tumor-free at the last follow up at 26 months after surgery.
The authors wrote this is not an unusual problem but that doctors need to be aware of the possibility in case they diagnose a chondroma, a non-cancerous tumor in the cartilage, or chondrosarcoma, a cancerous tumor. In the case of osteochondroma, it happens frequently that the patients don't even know they have one until it starts to block their motion, as it did in the patient described earlier. Usually, after the mass has been removed, the patient returns to normal after the rehabilitation.
Reference:
Vassilios S. Nikolaou, MD, PhD, et al. Giant Osteochondroma of the Posterior Cavity of the Knee. In Orthopaedics. November 2008. Vol. 31. Pp. 1142'
