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. When the inferior clivus is horizontal and linear, the basion is the most posterior point on that line.

x

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/

• dontoid

– 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: Linear perpendicular

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 NCW

BAI = 4.5mm NCW = 20mm

BAI = -2.3 mm NCW = 19 mm

Movement calculations

• C0-2: BAIflexion- BAIextension

C0-2= -2.3mm – 4.5mm = -6.8mm

• C1-2: NCWflexion- NCWextension

C1-2= 20mm – 19mm = 1mm

• C0-1: |C0-2| – |C1-2| (these are abs value)

C0-1= 6.8mm – 1mm= 5.8mm