Primary lipoma arborescens of the knee.

Lipoma arborescens is a rare and benign intra-articular lesion of unknown etiology; it is characterized by synovial villous proliferation and sub-synovial connective tissue replacement by mature fatty tissue. It is part of the differential diagnosis in patients with an articulation affected by a slow, progressive, and chronically inflamed affection. We report primary knee involvement in a patient without significant articulate antecedents. Lipoma arborescens was diagnosed after knee magnetic resonance imaging and was confirmed by an anatomopathological study of the surgical specimen.