Uncommon etiology of knee pain: Lipoma arborescens.

 Lipoma arborescens is a rare intra-articular benign tumor. It affects mostly the knee and the diagnosis is usually difficult due to resembling symptomatology of osteoarthritis. CASES PRESENTATION: We report herein 3 new cases of lipoma arborescens of the knee in which a patient has synovitis associated. In 2 cases, the discovery was intraoperatively. We also report a tumor relapse 2 years after surgery.