Boss wants to cancel my scheduled vacation?

I just had surgery on my left dominant arm. My expected time off of work will be approx. 6 weeks. Today the surgeon said I will probably be able to return to work one week before my planned 2 week vacation. I called my boss to let him know I would be returning to work for a week before my vacation. My boss said I will need to cancel and then reschedule my vacation, even though my vacation had been approved for 2 months. I wanted to tell him that I had booked hotel rooms with another family and my kids and was going out of state for those two week to see relatives who I have not seen in years. I believe that he is a bit upset because he can not go on vacation until I return. Do you think he has the power to cancel my scheduled vacation and should I call Human resources to verify his claim? Will human resources side with him or me?