MY DH had surgery for a neuroma about 8 years ago. He had no issues with numbing when riding after the surgery, although his foot still is "sensitive" when doing other activities, especially walking. In fact, the neuroma was caused by walking 50 city blocks in NYC in dress shoes. He was back on the bike about 6-8 weeks after the surgery and did the cycling leg of a pentathalon about 3 months after the surgery (it involved cycling up a mountain in NH), after little training.
I'm wondering if the numbness has to do with other things, as stated above. Your pedal stroke might be different now that your foot is "fixed."