Haemarthrosis is haemorrhage 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 haemarthrosis. Other causes include bleeding disorders, anticoagulation, neurological deficits, arthritis, tumours and vascular damage.
There is a wide overlap in the radiographic features of a haemarthrosis and joint effusions of other aetiologies.
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.
Ultrasound of a haemarthrosis may appear as a joint effusion with or without internal echoes depending on the age of the haemorrhage with layering of cells (haematocrit effect).
Treatment and prognosis
Management consists of removal of the underlying cause, e.g. correction of coagulation. Aspiration of haemarthrosis following trauma is controversial as needle insertion technically converts a closed fracture to an open one with increased infection risk.
In cases of haemophilia, recurrent haemarthroses can result in haemophilic arthropathy.