bruised fingers

While I was preparing dinner and cutting pieces of chicken I felt a sting on the middle finger. Within seconds my finger started to swell and later it turned blue. It became all bruised and I could not bend my finger with the swelling. The next day the bruises became darker and it seems that it is covering all my finger. My doctor says that I must have broken a vein from the inside. Please what do you think this is. Thank you.