Pigmented villonodular synovitis (PVNS) is a rare joint disease caused by the proliferation of synovial tissue, leading to significant pain and joint destruction. It typically begins between the ages of 30 and 50 and significantly affects patients' functionality. The proliferation is due to somatic mutations in some fibroblastic cells within the tissue, which triggers a massive recruitment of inflammatory cells. The condition is considered a benign tumor of the synovial membrane with a major inflammatory component. Diagnosing PVNS requires synovial tissue analysis, obtained either through surgical excision or guided needle biopsy. This biopsy technique, done as an outpatient procedure, is well tolerated and helps confirm the diagnosis before treatment. Our goal is to better understand this disease and determine if the analysis of synovial tissue could serve as a useful biomarker for patient management in the context of personalized medicine.

This is a prospective, multicentre, open-label study focusing on the collection and analysis of synovial tissue samples from PVNS patients. The study aims to explore the pathophysiology of PVNS and identify prognostic and predictive biomarkers.

Inclusion Criteria: Adults diagnosed with localized or diffuse PVNS, referred for therapeutic management.

Exclusion Criteria: Minors, pregnant or nursing women, individuals under guardianship, patients with severe thrombocytopenia, those on therapeutic anticoagulation, and patients declining participation.

Synovial tissue will be obtained either during surgical intervention (if indicated) or through guided needle biopsy. The biopsy is intended to be diagnostic and will also serve for research purposes. Samples will be analyzed using histological, immunohistochemically, and high-throughput methods.

Patients will be followed one year with two systematic visits (6 months and 1 year after the biopsy). At each visit, they will have a standardized clinical evaluation to assess pain, function and response to treatment. Thereafter, they will be followed as required by the clinical routine over a 4-year period, including clinical assessment and response to treatment.

The primary Outcome is the successful establishment of a patient cohort and synovial biocollection. The secondary Outcomes are the following: Tissue quality, biopsy tolerance, patient acceptability, and the effects of treatments on synovial explants.

Statistical Analysis: The study will include descriptive and predictive analyses, focusing on correlations between synovial abnormalities and clinical progression or treatment response.

Inclusion Criteria:

• Patient >18 years
• Diagnosis of localized or diffuse villonodular synovitis
• Referred for therapeutic management
• Affiliated with or benefiting from a social security scheme

Exclusion Criteria:

• Minors
• Pregnant women
• Nursing mothers
• Protected patients: patients under guardianship or curatorship, safeguard of justice
• Patients deprived of liberty
• Curative anticoagulation
• Thrombocytopenia < 50,000 platelets/mm3