Hi ~ I really don't know what to tell you. You may need to have a C-scan to see if there is something pinching a nerve that is making you numb. That would be the only other reason I could think of that would make you numb. If there is nothing, then the nerve is damaged. There would be nothing you could do for that.
Ask your doctor for a C-scan - you can't have an MRI I don't believe because of the fusion - and you probably have instrumentation, i.e. screws, plates. But you can have a C-scan. So ask if he can see if there's a nerve being pinched or compromised. It's worth a try.
I've had a numb leg/foot for 25 years so sometimes you've just gotta live with it unfortunately. It really bites! LOL
I hope your doc will agree to the scan so you'll know for sure. God bless and take care. Hugs, Lee