THere can be nerve damage as a sequelae of such knee surgery. This is probably the cause of the numbness. Motor and sensory nerves are different and so one or the other, or both can be affected.
This may or may not recover over a period of months.
Agree with waverider that this should be discussed with your surgeon.
Best chance for recover will be assisted if you can maintain excellent and close to normal blood sugar control (Non-diabetic normal a1c is < 5.0, and if you can get your A1c safely lower towards 5 - suggest low carb diet - Dr. Berstein: Diabetes Solutions has a good approach), this will assist.
Hope you are better soon. Take extra good care of your feet if you have loss of sensation.
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