Intra-articular lipoma arborescens of the knee joint.

Intra-articular lipoma arborescens (LA) is a rare entity that can present with monoarticular or polyarticular involvement of joints such as knees, ankles, hips, shoulders, and elbows. We describe a case in a 26-year-old man who presented with intermittent pain and swelling of the left knee joint for the previous 2 years. Physical examination showed only tenderness over the medial line of the left knee joint. MRI found only joint effusion; therefore, the patient was referred to the orthopedic clinic where he underwent arthroscopy, which revealed a diffuse yellow soft tissue synovial papillary growth involving both medial and lateral gutters of the suprapatellar pouch. A biopsy reported intra-articular LA. This is the first case of LA reported in Saudi Arabia. LA should be included in the clinical and radiologic differential diagnosis of cases with persistent knee joint effusion.