"Trauma is by far the most common cause of a haemarthrosis. Other causes include bleeding disorders, anticoagulation, neurological deficits, arthritis, tumours and vascular damage."
"Haemarthrosis displaces normal structures, for example in an elbow, anterior and posterior fat pads may be elevated or visible respectively. In the knee, there may be anterior displacement of the patella and quadriceps tendon. In the shoulder, the humerus may be inferiorly displaced, mimicking a dislocation."
"There is a wide overlap in the radiographic features of a haemarthrosis and joint effusions of other aetiologies."