My son has swollen tounge after ankle surgery. it hurts really badly as if he bit it, but there are no bite marks of any kind. what can this be?

Anesthesia: The swollen tongue is most likely due to some trauma from obtaining an airway for the surgery (assuming it was general anesthesia). Less likely, he could be having an allergic reaction to medication. I recommend you contact the surgeon and/or anesthesiologist if the symptoms persist.

Allergy: He could possibly be allergic to any medication for the ankle surgery.

Not REALLY connected: It isn't a direct result of the ankle surgery, but he must have some sort of allergic reaction to one of the chemicals or medications he was given. Check to see if they used a prophylactic antibiotic just before the procedure. This would be a likely culprit, especially if any surgical hardware was used.

After: Was it right after surgery? If so report it to where he had surgery. He is having an allergic reaction and if younger continues to swell get him to er before he has breathing issues. All the best!