Spontaneous recurrent hemarthrosis of the knee joint in elderly patients with osteoarthritis: an infrequent presentation of synovial lipoma arborescens.

Synovial lipoma arborescens (SLA) is a rare, benign, fat-containing synovial proliferative lesion that is typically known to affect the knee joint in adults, although it has also been described in other joints. SLA usually presents as a painless swelling and recurrent joint effusion, and the laboratory test results, including aspirated synovial fluid, are usually normal. We present here two cases of SLA of the knee, which presented as spontaneous recurrent hemarthroses in elderly patients with osteoarthritis (OA) with bloody aspirated synovial fluid. Magnetic resonance imaging (MRI) and arthroscopic synovectomy suggested the diagnosis of SLA; the histopathologic examination confirmed the diagnosis. One year later, both patients remain symptom-free and report no new episodes of hemarthrosis. We postulate that SLA should be included in the differential diagnosis of patients with recurrent joint effusions with hemarthrosis in elderly patients with OA. The clinical presentation, MRI findings, and treatment of SLA are described, and the entity is briefly reviewed.