I have always learned to rely on my intuition. Mechanism of injury is a driving force, but sometimes you just "have that feeling". We had a patient that sustained major trauma at a mountain bike race. Despite his combativeness (head injury induced), we managed to c-spine him at least partially (he is an EMT, and was getting out of the straps faster than we could get him into them. Pulled his c-collar off TWICE and pulled his head up after we secure him to the board, pulling the Sta-Bloks up with him. It was a fight keeping him calm and on the board without meds - We are BLS.) until we could transfer care to the local medics and the air evac he required. Turns out he sustained a C1, C2, C3 fracture, along with a basilar skull fx, frontal lobe contusions, and other injuries.