We don't use quite the same joint protocol as Marie (although at least one of our surgeons would be in heaven!) We are extremely picky about sterility in a joint replacemtn though.
Why is there more concern about infection in an ortho procedure than, say, a vascular procedure?
Think of the perfusion... the body can't fight infection as well in bone. Osteomylitis is an ugly thing!
If there is colonization of hardware... it may need to come out. Patient gets another THR?? Don't want that!
The general idea is to get the prophylactic abx in the body as close (late) to incision time as possible, hence sending it to the OR vs giving in pre-op. You want your peak levels during the procedure.
But... (as an aside) back to perfusion... a tourniquet is used during a total knee so the abx would need to be in before the tourniquet is inflated or it will go everywhere but the op leg... then what's the point?
Same deal as anytime you give abx to any patient in any setting, remember your 5 rights. Sounds like your instructor threw you a "trick" question