Hemarthrosis is hemorrhage into a joint space and can be regarded as a subtype of a joint effusion.
Trauma is by far the most common cause of a hemarthrosis. Other causes include bleeding disorders, anticoagulation, neurological deficits, arthritis, tumors and vascular damage.
There is a wide overlap in the radiographic features of a hemarthrosis and joint effusions of other etiologies.
Hemarthrosis 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.
Ultrasound of a hemarthrosis may appear as a joint effusion with or without internal echoes depending on the age of the hemorrhage with layering of cells (hematocrit effect).
Treatment and prognosis
Management consists of removal of the underlying cause, e.g. correction of coagulation. Aspiration of hemarthrosis following trauma is controversial as needle insertion technically converts a closed fracture to an open one with increased infection risk.
In cases of hemophilia, recurrent haemarthroses can result in haemophilic arthropathy.