Can a femur bone spiral fracture occur without abuse in a 5 week old infant?

No. This would be caused by abuse.

The analysis of . Fracture pattern, location, cause, age, other injuries, other obvious trauma, history, presence or absence of obvious trauma ( ie if it seems that a low energy injury results in fracture) are all considerations in the careful evaluation of whether an injury to a child is related to abuse or not. There are several bone and growth plate disorders that can lead to fragile bones look at all of it.