Instructions to reviewers Reference lines Atlanto-planar line (APL) - PowerPoint PPT Presentation

Instructions to reviewers • Reference lines – Atlanto-planar line (APL) – Posterior axial line (PAL) • Quantitative assessment – Neural canal width (NCW) – Basion-axial interval (BAI)

Basion • Defined for our purposes as the most inferior point of extension of the clivus. x When the inferior clivus is horizontal and linear, the basion is the most posterior point on that line.

ACPRA (ant cortex post ring C1) • Defined as the most anterior point of the anterior cortex of the posterior ring of atlas (C1) x

JPO (Junction C2 pars/odontoid) • Defined as the intersection of the superior cortex of the C2 pars interarticularis with the posterior cortex of the odontoid process x

Reference lines • Drawn with arrow tool at 100% magnification – Posterior axial line • Vertical line drawn from the posterior inferior cortex of axis (C2) and the junction of C2 pars/ odontoid – Atlanto-planar line • Horizontal line drawn through the inferior aspect of the anterior and posterior rings of atlas (C1)

Measurements • Performed with length tool at 300% magnification – NCW : Linear distance between ACPRA and PAL measured parallel to APL BAI – BAI : Linear perpendicular NCW distance between basion and PAL. BAI is positive when the basion is anterior to the PAL and negative when the basion is posterior to the PAL

BAI = 4.5mm NCW = 20mm

BAI = -2.3 mm NCW = 19 mm

Movement calculations • C0-2: BAI flexion - BAI extension C0-2= -2.3mm – 4.5mm = -6.8mm • C1-2: NCW flexion - NCW extension C1-2= 20mm – 19mm = 1mm • C0-1: |C0-2| – |C1-2| (these are abs value) C0-1= 6.8mm – 1mm= 5.8mm