Are the Home, Search and Back Buttons part of digitizer?

Hi there,

before I go ahead with another repair, just wanted ask if anyone can confirm whether the Home and Back buttons at the bottom of the HTC sensation are just part of the digitizer assembly and do not need to replaced separately?

We cracked the screen on a 1 week old phone and after having it replaced the buttons stopped working 2 days later and the repairer claims we need to replace the digitizer again...at my cost of course.

If he replaces the digitizer screen will that also replace the buttons?

Thanks for any help!!!!

Andy