Instructions to reviewers Reference lines Anterior axial line (AAL) - PowerPoint PPT Presentation

Instructions to reviewers • Reference lines – Anterior axial line (AAL) • Quantitative assessment – Atlanto-axial interval (AAI) – Condyle-axial interval (CAI)

Reference line • Drawn with arrow tool at 100% magnification – Anterior axial line (AAL) • Line along the anterior border of the C2 body and dens extending into the cranial space. If the bone curves or scallops, draw the most easily reproducible line possible

Measurements • Performed with length tool at 300% magnification – AAI : Linear distance between the ALL and the posterior border of the anterior C1 arch. If the posterior cortex of the anterior arch of C1 is irregular in contour, then choose the smallest distance CAI available based on a single reproducible landmark AAI – CAI : Linear perpendicular distance between cephalad extension of the anterior axial line and the anterior border of the occipital condyle (the same point must be seen between each x-ray). Positive value when condyle is anterior to the AAL, negative value when condyle is posterior to the AAL.

CAI: 2.0mm AAI: 4.8mm

CAI: -3.1mm AAI: 3.8mm

Movement calculations • C0-2: CAI flexion - CAI extension C0-2 = 2.0mm – (-3.1mm) = 5.1mm • C1-2: AAI flexion - AAI extension C1-2 = 4.8mm – 3.8mm = 1.0mm • C0-1: |C0-2| – |C1-2| (these are abs value) C0-1 = 5.1mm – 1.0mm = 4.1mm