You have a pinched nerve. Did you do anything or experience pain in your knee, leg or back before you noticed the numbness? If not taken care of it can become permanent and cause other problems. Best wishes, Sissie
Is the numbness just in your knee?
Do you experience a numb feeling or sensation down the side of the outer thigh as well?
Like bigsissie says, it sounds that there is pinched nerve somewhere. Sometimes it is not in the actual joint itself, but can be referred from elswhere.
The other problem than can cause the numbness is from inflammation of the joint due to arthritic conditions.
I would suggest you get it examined by the doctor who will probably send you for an xray to see if this is a problem with the bones or whether there is a problem with ligaments and muscles.
I feel numbness in both my knees, one is from osteoarthritis due to the inflammation, the better one is due to trappend nerves in the groin called meralgia parasthetica.
Only by examination of the knee will you know what is causing your problem.
I sustained an injury to my back about a year and a half ago. But I wouldn't have thought that would have been associated with it considering everyone I have seen about it has passed it off as my back being a muscular problem. So I didn't think that injury had any association with it.
A couple of years ago I experienced a numb feeling on my left knee and slight pain as well as a numbness that ran down the outside of the same leg. It was diagnosed as meralgia parasthetica which is a trapped nerve in the groin area. The area is still numb and lacking in sensation.
Your particular back injury may not have any assocation with your knee problem, but there is some pinching of a nerve somewhere. Only a visit to the doctor for a full medical examination will be able to give you the correct answer and how to get it treated or a referral to the physiotherapist for advice and exercise to help alleviate your symtoms.