Pigmented Villonodular Synovitis of the Knee: An Underappreciated Source of Pain in Children and Adolescents.

BACKGROUND: Pigmented villonodular synovitis (PVNS) is a benign proliferative synovial disorder most commonly described in adults. The purpose of this study is to describe the presentation and management of a large single-center series of pediatric patients with PVNS of the knee.

METHODS: A retrospective review was performed of consecutive pediatric patients treated for PVNS at a single institution from 2001 to 2016. Inclusion criteria were patients below 20 years of age with surgical treatment of histologically proven PVNS of the knee. Review of the electronic medical record was utilized to gather demographic data, clinical presentation, affected joint, imaging findings, treatment, and disease persistence.

RESULTS: Over the 16-year study period, 17 pediatric patients with an average age of 11 years (range, 3 to 19 y) were treated for PVNS of the knee. The average duration of symptoms before orthopaedic evaluation was 16 months. More than half of the children were misdiagnosed with a variety of rheumatologic or orthopaedic conditions before their diagnosis of PVNS. On the basis of magnetic resonance imaging (MRI), PVNS was included as a potential diagnosis in 12 of 17 patients (71%). A total of 27 surgeries were performed in 17 patients. Ten patients were treated with a single surgery and 2 patients were treated with staged biopsy followed by synovectomy. Five patients required ≥2 therapeutic surgeries. The majority of procedures were arthroscopic synovectomies (89%). One patient required open resection of a mass in the posterior compartment of the knee and 1 patient had a manipulation under anesthesia for arthrofibrosis. Ten patients were noted to have nodular disease, 4 diffuse, and 3 mixed. At an average 15-month follow-up, 15 patients (88%) were considered to be disease-free based on clinical examination and/or follow-up MRI. Two patients (12%) had MRI studies following their last surgery with findings consistent with persistent PVNS, but only a single patient had persistent symptoms.

CONCLUSIONS: This case series of pediatric patients with PVNS of the knee represents the largest single-center cohort in the literature. Although previously considered a disease of young adult patients, PVNS should be considered in pediatric patients with an insidious onset of joint swelling with or without pain. Symptoms may be present for months to years before diagnosis. Patients are frequently misdiagnosed, most commonly with rheumatologic diseases, bleeding disorders, or septic arthritis. MRI with gradient echo sequences is the diagnostic imaging study of choice and arthroscopic synovectomy produces good outcomes with low rates of symptomatic disease persistence.

LEVEL OF EVIDENCE: Level IV.