What Causes Purple Discolouration And Swelling In Shin After An Injury?

I am a healthy 72 yr old female. I banged my shin about three weeks ago and the bruise still looks purplish and is slightly swollen and a bit tender. In Peru, where I used to live, a product called Hirudoid was in everyone s first aid kit and was used extensively on bruises and contusions. Is it available in the US?