Predental space (anterior aspect of odontoid to post aspect of ant ring of C1)
Adult <3mm
Peds <5mm
Widening of space suggests Jefferson burst fracture of C1
Anterior soft tissue
Distance between ant border of C2 and post pharynx should be <6mm in adults and peds
Distance between ant border of C6 and post trachea should be <22 mm in adults
Should be <14mm in children <15yr or less than width of vertebral body at each level
Bones
Vertebral body: Anterior height should be no more than 3mm shorter than posterior height
Adult <3mm
Peds <5mm
Widening of space suggests Jefferson burst fracture of C1
Distance between ant border of C2 and post pharynx should be <6mm in adults and peds
Distance between ant border of C6 and post trachea should be <22 mm in adults
Should be <14mm in children <15yr or less than width of vertebral body at each level
Should be <14mm in children <15yr or less than width of vertebral body at each level
Vertebral body: Anterior height should be no more than 3mm shorter than posterior height
Cervical spine x-ray interpretation
Chest x-ray interpretation
Canadian cervical spine rule
X-ray interpretation 
Neck diagnoses
Tongue diagnoses
NEXUS cervical spine rule
Predicting the difficult airway