hello there!
i had an accident over 2 years ago and landed directly on my kneecap.
i had a lot of numbness in my knee initially too and had x rays,ultra sounds,mri etc etc and nothing really was found.
i got more opinions as i knew something was not rgiht.
i then had an operation (keyhole surgery),the results brought back alot of internal problems the other scans etc had missed.
have you had a specialist appointment with someone who specialises in knees??
doctors know the basics of things but i would try and get a referal to a specialist in knees to get a better and more indepth opinion.
take care,keep posting how you get on!
claire