The synovium is a layer of tissue that lines the joints. It also produces fluid to lubricate the joints.

In pigmented villonodular synovitis (PVNS), the synovium thickens, forming a growth called a tumor.

PVNS isn’t cancer. It can’t spread to other parts of the body, but it can grow to the point where it damages nearby bones and eventually causes arthritis. Excess growth of the joint lining also causes pain, stiffness, and other symptoms.

PVNS is part of a group of noncancerous tumors that affect the joints, called tenosynovial giant cell tumors (TGCTs). There are two types of PVNS:

  • Local or nodular PVNS affects just one area of the joint or only the tendons that support the joint.
  • Diffuse PVNS involves the whole joint lining. It can be harder to treat than local PVNS.

PVNS is a rare condition. It affects only about 2 out of every 1 million people.

Doctors don’t know what exactly causes this condition. There may be a link between PVNS and having a recent injury. Genes that affect the growth of cells in the joint could also play a role.

PVNS may be an inflammatory disease, similar to arthritis. Researchers have discovered higher levels of inflammatory markers such as C-reactive protein (CRP) in people with this condition. Or, it may stem from unchecked cell growth, similar to cancer.

Although PVNS can start at any age, it most often affects people in their 30s and 40s. Women are slightly more likely to get this condition than men.

About 80 percent of the time, PVNS is in the knee. The second most common site is the hip.

PVNS can also affect the:

  • shoulder
  • elbow
  • wrist
  • ankle
  • jaw (rarely)

It’s uncommon for PVNS to be in more than one joint.

As the synovium enlarges, it produces swelling in the joint. The swelling can look dramatic, but it’s usually painless.

Other symptoms include:

  • stiffness
  • limited movement in the joint
  • a popping, locking, or catching feeling when you move the joint
  • warmth or tenderness over the joint
  • weakness in the joint

These symptoms may appear for a period and then disappear. As the disease progresses, it can cause arthritis in the joint.

The tumor will continue to grow. It left untreated, it will damage nearby bone. The main treatment for TGCT is surgery to remove the growth. Surgery can be performed in several different ways.

Arthroscopic surgery

This minimally invasive procedure uses several small incisions. The surgeon places a thin, lighted scope with a camera through one of the incisions. Tiny instruments go into the other openings.

The surgeon can see inside the joint on a video monitor. During the procedure, the surgeon will remove the tumor and the damaged areas of the joint lining.

Open surgery

Sometimes small incisions won’t give the surgeon enough room to remove the entire tumor. In these cases, surgery is done as an open procedure through one large incision. This lets the doctor see the entire joint space, which is often necessary for tumors in the front or back of the knee.

Sometimes, surgeons use a combination of open and arthroscopic techniques on the same joint.

Joint replacement

If arthritis has damaged a joint beyond repair, the surgeon can replace all or part of it. Once the damaged areas are removed, replacement parts made from metal, plastic, or ceramic are implanted. Tumors usually won’t return after a joint replacement.

Tendon repair

PVNS can eventually damage the tendon in a joint. If this happens, you can have a procedure to sew the torn ends of the tendon back together.

Radiation

Surgery isn’t always successful at removing an entire tumor. Some people aren’t good candidates for surgery, or they prefer not to have it. In these cases, radiation may be an option.

Radiation uses high-energy waves to destroy the tumor. In the past, radiation treatment came from a machine outside the body.

Increasingly, doctors are using intra-articular radiation, which injects radioactive fluid into the joint.

Medication

Researchers are studying a few drugs for PVNS in clinical trials. A group of biologic drugs may help prevent cells from collecting in the joint and forming tumors. These drugs include:

  • cabiralizumab
  • emactuzumab
  • imatinib mesylate (Gleevec)
  • nilotinib (Tasigna)
  • pexidartinib

How long it takes to recover depends on the procedure you’ve had. It can take a few months to recover after open surgery fully. Typically, arthroscopic surgery results in a faster recovery time of a few weeks or less.

Physical therapy is key to a speedy recovery. During these sessions, you’ll learn exercises to re-strengthen and improve flexibility in the joint.

It’s important to rest the affected joint when it’s painful, and after you have surgery. Take pressure off weight-bearing joints like the knee and hip by staying off your feet and using crutches when you do walk.

Regular exercise can help you retain movement in the joint and prevent stiffness. A physical therapist can show you which exercises to do, and how to do them safely and effectively.

To reduce swelling and pain, hold ice to the affected joint for 15 to 20 minutes at a time, several times a day. Wrap the ice in a towel to prevent it from burning your skin.

Surgery is usually very successful at treating PVNS, especially the local type. Between 10 percent and 30 percent of diffuse tumors grow back after surgery. You’ll see the doctor who treated you for several years after you have surgery to make sure your tumor hasn’t returned.