An Uncommon Cause of Knee Locking – Pigmented Villonodular Synovitis (PVNS)
PVNS or pigmented villonodular synovitis is an uncommon condition that I see from time to time. This is a benign tumour involving the inner lining of a joint. I treat about 3 to 4 such cases each year. Although it can affect any joint in the body, the most common joint with this problem that I encounter is that of the knee joint.
What is PVNS?
Pigmented villonodular synovitis (called PVNS for short) is a joint problem that usually affects the knee. It can also occur in the shoulder, ankle, elbow, hip, hand or foot.
When you have PVNS, the lining of a joint becomes swollen and grows. This growth harms the bone around the joint. The lining also makes extra fluid that can cause swelling and make the joint hurt.
Who Gets PVNS?
PVNS is not common. It usually affects people 20 to 45 years old, but it can also occur in children and people over 65 years old. Both men and women can suffer from this problem.
We do not know what causes PVNS. Some people with PVNS remember that they hurt their joint at some time in the past.
For unknown reasons, some or all of the synovial lining tissue of a joint occasionally undergoes a change and becomes diseased, wherein the joint lining tissue becomes thick and overgrown and accumulates a rust-colored, iron pigment known as hemosiderin. Strange, foamy cells and large (so-called “giant”) cells with many nuclei also appear. The overgrowth of the joint lining tissue can occur diffusely throughout a joint by way of a generalized thickening of the entire lining membrane, or a localised area of synovial membrane can overgrow and form a discrete nodule (tissue mass) that remains attached to the rest of the internal joint lining by way of a stalk. While this disease process does involve abnormal tissue growth, it is uniformly benign and has not been known to metastasize as do malignant growths. PVNS can be considered a benign, “neoplastic” (tumor growth) process, with some varieties being more aggressive in their growth and thus harder to treat, and other varieties being less aggressive in their growth and thus easier to treat.
What Are the Symptoms?
The common symptoms are swelling of the affected joint. As the knee joint is the most commonly affected joint in PVNS, the person may have swelling of the knee joint.
It can also cause pain due to erosion of the articular cartilage of the joint by the locally aggressive tumour.
Sometimes the person with PVNS may present with acute swelling and pain in the knee. There may be a history of pain after getting up from a squatting position. The knee joint may become locked due to the tumour blocking knee extension.
How t0 Diagnose PVNS?
PVNS can look like arthritis and some other conditions.
After a physical exam, x-rays of the joint that hurts may be useful.
Your doctor may also want to draw some fluid from the joint and test it.
Another test, magnetic resonance imaging (also called MRI), takes a “picture” of the joint.
What is the Treatment?
The best way to treat PVNS is to remove the lining of the joint. This can be done with regular surgery (sometimes called “open” surgery) or with arthroscopy. In arthroscopy, the doctor makes a tiny cut in the skin over your joint. Then a thin tube is put into the joint to remove the lining.
Even with treatment, PVNS comes back about half of the time. If the pain comes back again and again, radiation therapy may help. Sometimes, the joint may need to be replaced.
This is a video of a patient who presented with acute knee locking (inability to straighten the knee) after getting up from a squatting position. MRI showed nodular PVNS in the right knee.
Arthroscopic resection of the PVNS tumour together with thorough arthroscopic synovectomy was performed.
This is the picture of the tumours that were removed:
Pigmented villonodular synovitis (PVNS) is a locally aggressive synovial tumour. There are two forms of PVNS: diffuse and nodular. Nodular occurs most commonly in the hands and diffuse is found most commonly in the knee. PVNS may also occur in the hips and ankle.
Treatment of PVNS is surgical excision.
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