You might want to do some reading on assisted hatch. (if you haven't already) Sometimes they hatch on their own with an unabsorbed yolk. Other times that can be a complication with an assisted hatch. Sometimes, when a hatch is assisted, and the chick still has yolk to absorb, or blood vessels that aren't dried up yet, the chick is left in the bottom part of the egg shell, with it supported in a cup while the rest of the yolk/blood vessels absorb/dry up. You might dab a bit of betadine or antibiotic ointment on the open wound. Keep it in the incubator and as clean as possible (or if you've put it in the brooder, keep it separated from it's hatch mates until the wound is healed. Perhaps keep it on paper towels or a cotton towel... no shavings until healed. I'm guessing that your incubator temp was a bit low. You might want to tweak it up a bit for the next hatch.
