Intraarticular fibroma of the posterior compartment in the knee. A case report.

Posterior knee discomfort and recurrent effusion of the left knee occurred in a 49-year-old man without a history of specific trauma. Magnetic Resonance Imaging (MRI) and an arthroscopic examination revealed a soft tissue mass arising from the posterolateral capsule. The microscopic diagnosis was a fibroma, which is a rare entity in this location. To the best of our knowledge, only four cases of fibroma in the knee have been reported. It was reported that more than 99% of fibromas arise from tendon sheaths or tendons. They sometimes present a diagnostic problem due to their relative rarity in this location and obscure histological features. Fibroma should be included in a differential diagnosis of a soft tissue tumor arising from the knee joint. However, an arthroscopic excision was curative in our case.