Fig. 20.

Intra-articular fractures. Lipohaemarthrosis. a Sagittal sonogram on the suprapatellar recess obtained in a patient with post-traumatic knee effusion and pain with negative radiographs. b Horizontal bean radiograph. In note a, the presence of an effusion inside the suprapatellar recess presenting a three-layered appearance separated by two fluid–fluid levels (arrowheads). The superior layer is hyperechoic and corresponds to fat (F) and the thin middle hypoechoic layer corresponds to serum (S), while the deep layer is due to sedimentation of cells content (CC). Radiograph (B) confirms the presence of intra-synovial fat (F) floating on blood (B), but cannot visualise the serum content. CT (not shown) showed an occult non-displaced fracture of the tibial plateau