CASE REPORTS: intraarticular fibroma of the tendon sheath in the knee.

We report a rare case of fibroma of the tendon sheath in the knee. To our knowledge, only three previous cases of fibroma of the tendon sheath in the knee have been reported in the English literature. In our case, T1-weighted magnetic resonance imaging revealed a low intensity signal, T2-weighted magnetic resonance imaging showed a mixed area of high and low signal intensity, and gadolinium-diethylene triaminepentaacetic acid-enhanced magnetic resonance imaging showed faint enhancement at the periphery of the lesion. Magnetic resonance imaging therefore was valid for detection of this intraarticular lesion. The lesion, which was located between the posterior capsule of the left knee and the posterior cruciate ligament, was excised arthroscopically.