What is Pigmented Villonodular Synovitis (PVNS) of the Knee
Pigmented villonodular synovitis (PVNS) of the knee is a rare condition characterized by overgrowth and thickening or swelling of the synovium (a thin layer of tissue that lines the joints and tendons), resulting in a growth called a tumor. The tumor or mass that occurs from this overgrowth is benign (noncancerous) and does not metastasize (spread) to other regions of the body. However, PVNS is a progressive joint disease that gradually worsens and can cause bone damage and arthritis.
In a healthy joint, the synovium produces a small amount of fluid that lubricates the cartilage and aids in joint movement. However, in PVNS, the synovium produces extra fluid, causing swelling in the joint and making movement very painful.
Although PVNS can affect any joints, such as the shoulder, ankle, elbow, and wrist, it most commonly affects the knee (about 80 percent of the time) followed by the hip. The condition can occur in people of all ages; however, it most often occurs in people in the age group of 20 to 50 years.
Types of Pigmented Villonodular Synovitis (PVNS) of the Knee
PVNS is categorized into two types: local or nodular PVNS and diffuse PVNS.
The local type affects one area of the joint lining or the tendons that support the joint. This type normally responds well to treatment.
The diffuse type is more widespread and aggressive and affects the entire lining of the joint. It is more difficult to treat this type.
Causes of Pigmented Villonodular Synovitis (PVNS) of the Knee
The exact cause of PVNS is unknown. However, genetic changes linked with this condition have been noted, but no clear evidence of a genetic cause is available at this time. In some individuals with PVNS, a small number of cells in the affected joint lining have a fault that causes them to produce a protein known as colony-stimulating factor 1 receptor (CSF-1R). Research has indicated that this protein is associated with PVNS.
Signs and Symptoms of Pigmented Villonodular Synovitis (PVNS) of the Knee
Some of the common signs and symptoms of PVNS may include:
- Joint effusion
- Joint instability
- A catching, locking, or popping sensation on joint movement
- Restricted range of motion
- Hemarthrosis (collection of blood in joint space)
Diagnosis of Pigmented Villonodular Synovitis (PVNS) of the Knee
When you present with the above symptoms, your doctor will review your medical history and perform a thorough physical examination of your knee. In order to obtain additional information and confirm the diagnosis, your physician may order further tests such as:
- X-rays to obtain clear pictures of the affected bone in order to detect any damages or changes in the bone, as well as to rule out other causes of pain.
- Magnetic resonance imaging (MRI) scan to obtain clear images of soft tissue structure surrounding the bone. MRI helps to detect a nodular mass, extensive thickening of the joint lining, as well as cartilage damage and destructive bone changes.
- Joint aspiration in which the joint fluid is removed using a syringe and analyzed for the presence of blood. In numerous cases of PVNS, the fluid in the joint is found to be bloody.
- Biopsy examination in which a sample of the tumor tissue is extracted through a small operation in the knee and analyzed under a microscope.
Treatment for Pigmented Villonodular Synovitis (PVNS) of the Knee
Treatment for PVNS usually involves surgery to remove the tumor and the damaged sections of the joint lining. This can be obtained through different surgical approaches, including:
- Arthroscopic surgery: This is a minimally invasive surgical method in which a few small keyhole incisions are made around the joint area. An arthroscope, a narrow tube with a tiny camera on the end is inserted through one of the incisions to view the knee joint. Specialized instruments are inserted into the joint through other small incisions. The camera attached to the arthroscope displays the image of the joint on the monitor. With the images from the arthroscope as a guide, your surgeon can determine any pathology or anomaly and repair it through the other incisions with special instruments.
- Open surgery: Open surgery is performed in cases where the area of defect in the knee is difficult to reach with an arthroscope. In this method, a single long incision is made at the knee joint which allows your surgeon to view the entire joint space. Open surgery is often required for tumors that are located both in the front or back of the knee and facilitates complete removal of the mass and the joint lining.
- Combined open and arthroscopic surgery: This combined surgical approach is performed when much of the tumor mass is located in the back of the knee. During this procedure, open surgery is used to remove the mass and posterior joint lining at the back of the knee, whereas arthroscopic surgery is used to remove the anterior joint lining. This combined approach reduces the scale of surgery, enabling a quick and easy recovery.
- Joint replacement: This surgery is employed when the joint is damaged beyond repair due to the effects of advanced PVNS. Joint replacement is a surgical procedure in which damaged areas of the joints are removed and replaced with artificial joint components called prostheses. Tumors typically do not recur post joint replacement.
- Tendon repair: Tendon repair surgery is performed when PVNS has damaged only the tendon in a joint. Typically, an open approach is employed to reach the damaged tendon and the torn ends of the tendon are sewn back together.
Radiation therapy is normally reserved for patients who are not a candidate for surgery, who do not wish to undergo surgery, or for whom surgery has not been successful. Radiation therapy uses targeted doses of radiation/high-energy waves to shrink or destroy tumors in the knee joint from a machine outside the body. Due to advances in technology, doctors are increasingly using a new method called intraarticular radiation in which radioactive fluid is injected into the affected joint to eliminate tumors.
Drug therapy using specific medications to treat PVNS is under study. These medications particularly target the CSF-1R protein made by cells in the joint lining and have been known to be effective in some patients. These medications include:
- Pexidartinib (Turalio)
- Nilotinib (Tasigna)
- Imatinib mesylate (Gleevec)
Recovery from surgery will depend upon the type of surgery you have undergone. Arthroscopic surgery typically results in a quicker recovery time of a couple of weeks or less, after which you may return to your normal activities. Open surgery is more extensive; hence your recovery time may take about a couple of months or more. Physical therapy is crucial for a faster recovery. During your physical therapy sessions, your therapist will teach exercises to improve your joint flexibility and help strengthen the knee joint. Assistive devices such as crutches are recommended to help ease pressure on the affected joint or to keep weight off your sore knee. Over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) will also be prescribed to provide relief from pain and swelling. You may also apply ice packs to the treatment area for additional comfort.