Trauma
An initial plain film would be appropriate if there is a history of recent significant trauma, or even a history of minor trauma in an elderly patient.
Red Flags > MRI
Immediate MRI is appropriate in the presence of red flags such as bladder dysfunction, areflexia, saddle anesthesia, progressive motor weakness, a history of cancer, or the presence of fever, unexplained weight loss, or night sweats.
Reference
ACR recommendations.
Physician 2009;79(12):1067-1074.