Recurrence of pigmented villonodular synovitis of the knee: A case report with review of literature on the risk factors causing recurrence.

Rationale: Pigmented villonodular synovitis is a rare disease which may involve any joints. It has localized and diffuse forms, and the latter is more aggressive with a higher recurrence rate. Different treatments are applied to each form of the disease, but there is no standard surgical procedure or any consensus on whether adjuvant therapy should be used. Many factors may lead to recurrence of the disease; however, there is no reliable way to predict the recurrence.

Patient Concerns: A 21-year-old female patient presented with a one-year history of progressive pain of the right knee.

Diagnoses: Pigmented villonodular synovitis.

Interventions: We performed an anterior approach arthroscopic synovectomy and a posterior approach open synovectomy in the popliteal fossa, but the patient declined to take radiotherapy as a post-surgical adjuvant therapy. Then, she received a repeat arthroscopic synovectomy 20 months later because of the recurrent lesions, and a radiotherapy was performed 6 weeks after the second surgery.

Outcomes: There were no abnormal signs in the right knee on magnetic resonance imaging scanning 6 months after the second surgery. The range of motion of her right knee was normal.

Lessons: Pigmented villonodular synovitis is a rare disease which may involve any joints. Surgical resection plus adjuvant therapy is recommended for patients with risk factors of recurrence.