May 29th of this year the top of my left hand was cut badly working on an overhead door spring. there was no tendon damage and I had all the feeling in the all of my fingers even right after it happened. about 4 weeks ago I told the doctor at times my whole hand was going numb, but when it came back to me as soon as I put it down I had complete feeling in all fingers again on the inside of my hand. he gave me an injection for carpal tunnel now all of my fingers except pinky or numb. I am being told that this has nothing to do with the massive injury to my hand even though I have never had a problem until this, How long does the injection last and could it of triggered this numbness?