Lipoma arborescens of the knee.

Lipoma arborescens is a rare intraarticular lesion characterized by diffuse replacement of the subsynovial tissue by mature fat cells, producing villous transformation of the synovium. The etiology of this benign condition is unknown. The most typical site of involvement is the knee, most notably at the suprapatellar pouch, although other joints can be affected. Symptoms consist of gradual joint swelling, variable pain, motion range restriction, and intermittent joint effusions or bleeding. We report a case of lipoma arborescens and discuss the clinical features, diagnosis, and treatment of this disorder based on a literature review. Although it is rare, lipoma arborescens should be included in the differential diagnosis of patients with chronic joint swelling or hemarthrosis.