Spine Measurements¶

Key Measurements in Spine Imaging¶

Cervical Spine¶

Anterior Atlanto-Dental Interval (ADI) - Distance from the posterior arch of C1 to the anterior odontoid - Normal: ≤3 mm (adults), ≤5 mm (children) - Increased in atlantoaxial subluxation (RA, os odontoideum, trauma)

Posterior Atlanto-Dental Interval (PADI) - Distance from the posterior odontoid to the anterior posterior arch of C1 - PADI <14 mm = risk of cord compression - More clinically relevant than ADI

Powers Ratio - BC/OA ratio (basion-posterior arch / opisthion-anterior arch) - Normal ≤1.0; >1.0 suggests anterior atlanto-occipital dislocation

Cervical Lordosis (Cobb Angle) - Angle between the C2 inferior endplate and C7 inferior endplate - Normal: 20–40° lordosis

Thoracic and Lumbar Spine¶

Thoracic Kyphosis - T4 superior endplate to T12 inferior endplate - Normal: 20–45°

Lumbar Lordosis - L1 superior endplate to S1 superior endplate - Normal: 40–60°

Spondylolisthesis Grading (Meyerding) - Grade I: 0–25% slip - Grade II: 25–50% - Grade III: 50–75% - Grade IV: 75–100% - Grade V (spondyloptosis): >100%

Clinical Pearl

The PADI (posterior atlanto-dental interval) is more clinically relevant than the ADI for predicting cord compression in the upper cervical spine. PADI represents the actual space available for the cord, while ADI measures only the atlantodental relationship. A PADI <14 mm is associated with neurological deficit.

Key Points¶

ADI >3 mm (adults) indicates atlantoaxial subluxation
PADI <14 mm indicates risk of cord compression
Powers ratio >1.0 suggests atlanto-occipital dislocation
Meyerding grades spondylolisthesis by percentage of slip
Normal cervical lordosis 20–40°, thoracic kyphosis 20–45°, lumbar lordosis 40–60°

References¶

Cobb angle. Radiopaedia.org. Available from: https://radiopaedia.org/articles/cobb-angle
Meyerding classification of spondylolisthesis. Radiopaedia.org. Available from: https://radiopaedia.org/articles/meyerding-classification-of-spondylolisthesis
Atlantodental interval. Radiopaedia.org. Available from: https://radiopaedia.org/articles/atlantodental-interval
Savarese LG, Menezes-Reis R, Bonugli GP, Herrero CFPDS, Defino HLA, Nogueira-Barbosa MH. Spinopelvic sagittal balance: what does the radiologist need to know? Radiol Bras. 2020;53(3):175-184. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC7302896/
Koslosky E, Gendelberg D. Classification in Brief: The Meyerding Classification System of Spondylolisthesis. Clin Orthop Relat Res. 2020;478(5):1125-1130. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC7170696/