Villonodular synovitis (VNS) is a rare disease with an incidence of 1.8 per 1,000,000 inhabitants. VNS of the ankle has seldom been described and evaluated given its extreme rarity (2.5% of VNS cases). It presents an 11% recurrence rate. We report a continuous retrospective series with the main objective of clinically and radiologically evaluating these ankles searching for any risk factors of recurrence. At revision the study's main endpoint was the existence of local recurrence (radiological and clinical) and the secondary endpoint was the existence of tibiotalar osteoarthritis. The working hypothesis was that recurrence could be subclinical, warranting systematic imaging studies during follow-up.

The study was retrospective, conducted on seven patients (six males) whose mean age was 42 years treated over a period of 9 years (two diffuse forms and five localized forms). The initial treatment consisted in synovectomy via the conventional approach. Four patients also received adjuvant isotopic synoviorthesis treatment. The revision was clinical (MMTS, AOFAS, and OMAS scores) and radiological (standard and MRI) to evaluate the joint after-effects and search for recurrence.

Six patients were seen at a mean 6.5 years of follow-up. One case of early recurrence (4 years) was noted, with a major clinical manifestation because it was associated with joint destruction requiring arthrodesis, and one case of late asymptomatic recurrence (9 years), diagnosed radiologically on the follow-up MRI. The functional results remained good at follow-up (MMTS 77%, AOFAS 71, OMAS 71). Five of the six patients returned to their daily activities. At revision, no sign of osteoarthritis was observed. No risk factor for recurrence was demonstrated.

The hypothesis was confirmed with the existence of asymptomatic recurrence at revision, underscoring the value of systematic MRI at follow-up. Other than major joint destruction, the prognosis remains good even in case of recurrence. The literature emphasizes the existence of an initial diffuse form and partial surgical resection as risk factors of recurrence. None of the reports in the literature has proven that adjuvant treatment, whose modalities do not meet with consensus, reduces this risk.

Retrospective series, level IV.