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.

Swollen knee from PVNS

Swollen knee from PVNS

It can also cause pain due to erosion of the articular cartilage of the joint by the locally aggressive tumour.

pvns knee x-ray with erosion of patella

pvns knee x-ray with erosion of patella

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.

pvns knee x-ray

Soft tissue swelling seen on X-rays

Your doctor may also want to draw some fluid from the joint and test it.

pvns knee aspirate

pvns knee aspirate

Another test, magnetic resonance imaging (also called MRI), takes a “picture” of the joint.

pvns knee mri

Note the Nodular Tumours in front and behind the knee

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:

PVNS Tumours

PVNS Tumours removed from the Knee


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.

PVNS has the highest prevalence during the third and fourth decades and it affects males and females equally.
It presents as a painless or mildly painful joint with swelling. It can also cause acute severe pain and locking of the knee.

Treatment of PVNS is surgical excision.

For more information on PVNS, please contact us at 683 666 36 or email

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12 Responses to “An Uncommon Cause of Knee Locking – Pigmented Villonodular Synovitis (PVNS)”
  1. Michelle says:

    Is PVNS a result of scarring in the knee? I have history of scarring in the lateral fat pad and now have a nodule which is affecting my ability to walk. Are the two conditions related? Will an MRI always confirm presence of PVNS?

    • Dear Micelle,

      PVNS is not due to scarring in the knee.



      • Regina says:

        I hurt my knee in August 2012 by a bad fall on my knee and I that’s when I starting having to have problems I was diognoised with PVNS after 2 MRI showed an agressive soft tissue growth I feel the fall caused the PVNS. I have alot of pain. Will bad falls cause PVNS?

      • No. Falls/trauma etc do not result in PVNS.
        PVNS is a type of tumourous growth from the synovium (inner lining) of the knee joint.

  2. nick says:

    Could a knee injury at work bring on the symptoms of PVNS and i didn’t know i had it?

  3. Linds says:

    I just had surgery for this, and my dr. said it was unlikely to come back. He was able to get the whole tumor (quarter size) and the stalk. It did not appear to affecting any other part of my knee. According to this article, do I still really have a 50/50 chance of a tumor returning?

  4. TM says:

    MRI shows considerable amounts of “hemosidirin” in the soft tissues of my knee. Is this alone indicative of PVNS? Symptoms are intermittant locking, swelling/edema and motion is limited.

  5. TM says:

    Dr. Chang,

    Can PVNS originate after a previous arthroscopy? Are hemosiderin deposits a “normal finding” after knee arthroscopy? Does PVNS present similarly to a ganglion cyst?

  6. Brandy says:

    I have both nodular and diffuse PVNS in my knee. For 3 years it was treated as arthritis and I was given Euflexxa. One day I was walking and took one step and fell. My knee locked and I couldn’t walk. I had episodes of pain that were excruciating.
    I’m looking into the new clinical drug therapy because 6 months after surgery both the tumor and the diffuse growth has returned.
    Also, there have been a couple of rare cases of metastasis and one of the women was my age, barely in her 50’s and they discovered her tumor had spread to her legs and she had a pathological fracture. Then it spread to her pelvis and lungs and she died. She initially had benign biopsies and her doctor failed to take care of business and dropped the ball. So this condition, rare as it may be, always needs to be treated with diligence and biopsied as if it can become malignant. Don’t take my word— the study is reported under the National Institute of Health government website.

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