My husband had emergency knee surgery and our Italian vacation needs to be postponed. He'll be on crutches for about 6 weeks so air travel is tricky.
any suggestions?

What kind of suggestions are you looking for? Seems you'll need to cancel. If it were me, I'd wait until he was off crutches, completely healed and finished with physical therapy to reschedule.

Air travel can be done with airport wheelchairs. Not the best way to travel, but doable. May even let you bypass some lines, lol.

However, as Melnq8 says, you should not consider travel, other than for an emergency, until he has completed physical therapy. Even then you may need to cut back on some activities.