Haemarthrosis is bleeding into a joint (haem' means blood and 'arthrosis' means joint).
The joint can rapidly become hot and tense.
What causes an haemarthrosis?
Haemarthrosis may result from damage to blood vessels from injury or surgery, or spontaneously in bleeding disorders such as haemophilia.
How can a haemarthrosis swell so much?
Haemarthrosis can result in acute and painful knee swelling. It may seem impossible that the joint can swell so much, but the blood is contained by the capsule of the knee, and it is really the capsule that swells, becoming inflated like a balloon.
Illustration depicting the capsule swollen and distended. It would normally be deflated like a popped balloon.
How is haemarthrosis managed?
Larger amounts of blood after injury or surgery are generally aspirated with a needle and syringe. Aspiration can offer rapid relief of discomfort. If the knee swells up again straight after the aspiration, one should suspect a bleeding disorder or a blood vessel that needs tying off.
What happens if a haemarthrosis is not aspirated?
A small haemarthrosis may resolve on its own without aspiration. A larger bleed may leave residual blood in the joint, which can cause inflammation and internal scarring (arthrofibrosis).
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