Glossary
Haemarthrosis
Quick answer
Haemarthrosis, also spelled hemarthrosis, means bleeding into a joint. In the knee it usually causes rapid, tense swelling within a few hours of an injury and often signals a significant problem such as an ACL tear, kneecap dislocation or fracture, warns Doha knee surgeon Dr. Pablo Gelber at Aman Hospital.
What it means
Haem means blood and arthrosis refers to the joint. When a structure with a blood supply tears inside the knee, blood fills the joint space. This is different from the slower, clear fluid of an ordinary effusion.
It may be seen on MRI as fluid with layering, or confirmed when a doctor draws fluid off with a needle and finds blood.
Why it matters
In adults, a knee that balloons within a couple of hours of a sports injury has a high chance of an ACL tear. Other common causes are a kneecap dislocation, a peripheral meniscus tear or a fracture of the joint surface.
Haemarthrosis without a clear injury is less common and may point to a bleeding disorder, blood-thinning medication or, rarely, a growth in the joint lining. It should always be investigated.
How it is assessed and treated
Expect a careful examination, an X-ray to rule out fracture and usually an MRI. A very tense knee may be aspirated for comfort. Early care is rest, ice, compression, elevation and crutches if needed, then treatment of the cause. Do not assume a quickly swollen knee is just a sprain; get it checked within a few days.
Frequently asked questions
How do I know if there is blood in my knee?
Swelling that appears quickly, within hours of an injury, and makes the knee feel tight and hard to bend suggests blood. Only a doctor can confirm it.
Will the blood go away by itself?
The body reabsorbs it over a few weeks, but the injury causing it may still need treatment, so assessment is important.
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