MR imaging of hemophilic arthropathy of the knee: classification and evolution of the subchondral cysts.

Magnetic resonance imaging was performed to assess the subchondral bone of the knee in 64 patients with severe hemophilia A. Using this method, subchondral cysts could be detected and evaluated. We separated the cysts into four classes (LL, LH, HH, C) depending on their signal intensities on T1- and T2-weighted images. Follow-up studies, performed on 25 patients during a period of 10-30 mo after the initial examination, suggest that these four classes of cysts correspond to four successive stages. Morphological changes within a class of cysts were also observed. Although histological confirmation was not possible, this study demonstrated that magnetic resonance imaging allows a better understanding of the pathophysiology and the natural evolution of the subchondral cysts in hemophilic arthropathy.