Intra-articular nodular fasciitis of the knee: a rare cause of recurrent hemarthrosis.

A 20-year-old man presented with pain and recurrent hemarthrosis in the right knee. Magnetic resonance imaging of the knee showed a lesion with homogeneous low signal intensity on T1-weighted images and a heterogeneous, low to high signal intensity on T2-weighted images. At arthroscopy, the mass was located between the posterior cruciate ligament and the posterior knee joint capsule. The tumor was excised through a posterior approach and histologically diagnosed as a nodular fasciitis. Intra-articular nodular fasciitis is a very rare clinicopathologic entity. The current case showed the unique clinical feature of recurrent hemarthrosis at initial presentation, which has not been previously reported.