[Lipoma arborescens of the knee in a patient with ankylosing spondylitis: case report and literature review].

Lipoma arborescens (LA) is defined as a villous lipomatous proliferation of the synovial membrane with diffuse substitution of the synovial tissue by mature fat cells. The injury is very rare, involving the knee joint (suprapatellar region) and is associated with degenerative joint disease. We describe the case of a male patient, suffering from ankylosing spondylitis with monoarthritis of the right knee and swelling in suprapatellar region important. The diagnosis of lipoma arborescens was confirmed from the MRI of the right knee.