I don't know which country you are from so when you say 'middle name' I'm not sure if you mean a second forename/given name or whether you mean a different category of middle name. I know some countries class middle names as a separate category to forenames as they have different naming conventions where they will take both their mothers and fathers surnames.

I'm a frequent flyer with Etihad and my ticket usually just have my first and last name and I have had no issues.

Mike

EDIT: I couldn't see your country when I was typing my post. I now see you are from the USA and I believe you have the same naming conventions as the UK. You definitely shouldn't have any problems. I understand only first and last names are mandatory on your ticket and should be shown exactly as shown as in your passport (correct spelling and not shortened).