How could you get osteomyelitis without having a prior infection/abscess?

Great question. In patients who have not had surgery and now possess osteomyelitis, the typical cause is the spread of bacteria through the bloodstream. Even brushing our teeth can push bacteria into our bloodstream. Sometimes those bacteria land on a particular tissue and start an infectious process.
Hematogenous . Osteomyelitis is generally caused by contiguous spread from an adjacent soft tissue or wound infection or from hematogenous spread. In answer to your question hematogenous spread from transient bacteremia, which occurs frequently, would be most likely.