Overview
Pigmented villonodular synovitis (PVNS) is an uncommon, benign-but-aggressive condition of the joint lining (synovium), most often affecting the knee. The synovium grows abnormally and can fill the joint space, leading to recurrent inflammation and bleeding into the joint, which leaves iron-containing pigment (hemosiderin). Over time, this can damage nearby cartilage and cause ongoing pain, stiffness, and reduced motion. Symptoms can come and go, and some people experience locking from thickened synovial tissue.
Symptoms
PVNS commonly causes deep, aching joint pain along with swelling, often in a single knee. You may notice stiffness, reduced range of motion, and a feeling of catching or locking, especially with bending and straightening. Recurrent joint effusions (fluid buildup) can make the knee feel tight or unstable. Symptoms may worsen with activity and may not fully resolve between flare-ups.
Causes
The exact cause of PVNS is not fully understood, but it involves abnormal synovial cell proliferation that behaves like a growth of the joint lining. The condition frequently leads to small episodes of bleeding within the joint, and the resulting hemosiderin pigment contributes to the characteristic imaging findings and inflammation. PVNS can be localized (more focal) or diffuse (more widespread through the synovium), which affects how extensive symptoms and joint damage may be.
Risk Factors
PVNS most often affects adults, commonly between young adulthood and midlife, though it can occur outside this range. A history of joint irritation or minor trauma may be present in some people, but this is not considered a definite cause. Having one episode can also increase the risk of recurrence if the synovial disease is not fully controlled.
Prevention
There is no guaranteed way to prevent PVNS, because the underlying trigger is unclear. You can reduce the chance of aggravating joint inflammation by protecting the knee from repeated overload, using proper mechanics during sports or work, and gradually progressing activity. If you have persistent or recurring knee swelling, getting evaluated early may help limit secondary cartilage irritation.
How the Diagnosis Is Evaluated
Clinicians start with a history of chronic one-joint pain, swelling, stiffness, and any catching or locking, followed by a physical exam to assess effusion, tenderness, and range of motion. X-rays may be normal early but can show later joint changes when cartilage is affected. MRI is the key test because PVNS often has distinctive features related to hemosiderin in the synovium, and not every patient needs the same sequence of studies. In many cases, confirmation is ultimately made by tissue sampling or analysis if a biopsy is obtained.
Nonsurgical Treatment Options
Conservative care focuses on controlling symptoms and preserving motion. Anti-inflammatory medications such as NSAIDs and short-term joint rest or activity modification can reduce pain and flare-related swelling. Physical therapy is often used to maintain flexibility, strengthen surrounding muscles, and improve functional movement patterns. Image-guided corticosteroid injections into the knee may help reduce inflammatory pain and effusion in selected patients, especially when symptoms flare. For diffuse or recurrent disease, a specialist may discuss non-surgical medical options such as targeted drug therapy that addresses the underlying signaling pathway of PVNS; this approach is typically coordinated through orthopedic oncology or rheumatology.
When to Seek Medical Attention
Seek prompt medical evaluation if you have persistent knee swelling with pain lasting weeks, recurrent effusions, or mechanical symptoms like locking or inability to fully bend or straighten the knee. Get urgent care sooner if the knee becomes rapidly more swollen and hot, if you develop fever, or if you cannot bear weight. Also seek urgent attention for severe or rapidly progressive weakness, numbness, or sudden major loss of function.
Frequently Asked Questions
PVNS often causes persistent or recurrent deep knee pain with swelling, stiffness, and sometimes catching or locking.
Symptoms may fluctuate, but the underlying synovial disease often persists or recurs without targeted management.
Next Steps
If your knee pain and swelling keep returning or you notice locking or significant stiffness, schedule an orthopedic evaluation. Ask whether MRI is appropriate to assess for PVNS and to plan symptom-focused conservative care. If symptoms worsen quickly or you develop fever or inability to bear weight, seek urgent medical attention.