What's the risk of sciatic nerve injury in an intramuscular injection to the buttocks?

Small: Not that these cannot occur, but considering the number of these types of injections that are done, they are rare - especially done " by the books" or with the proper technique which is by giving it in the upper outer quadrant of the buttocks, away from the sciatic notch where the nerve is..

See below: If done correctly in the upper outer quadrant of your bottom the risk is essentially zero. If done elsewhere, especially more toward the middle the risk goes up.