Thanks for writing in.
If you had the injury 3 years back, it is most likely that you are suffering from the long term side effects of the knee injury
scan being normal shows that the ligaments and menisci are normal. It happen that your joint cartilage
has undergone some degeneration. This can cause irritation of nerve
endings which is perceived as pain. I suggest you consult a different orthopedician and get examined by him. If felt necessary, he may ask for X ray
or MRI scan to be repeated depending on clinical findings. Treatment might involve rest and medications.
Hope this helps