A VERY long time -- A hematoma (as you probably know) is when there is a large amount of internal bleeding -- in effect the blood and whatever antibodies are sent there are walled off -- and draining takes a long time because a lot of the small capillaries were broken.
I had a huge hematoma when I managed to run over my lower calf -- saved from being crushed because the wheel was held up by my clog. The occurred in 2000 and there is still a protuberance where the worst of the damage occurred as well as a large indentation -- the area is also numb and if I push hard there is some pain.
There is no pain when I walk however so it doesn't bother me.
Did you have a test to see if there the arteries are clear? It's some form of sonogram and is recommended when there is major damage to the circulatory system.
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