Powers Ratio (Atlanto-Occipital Dissociation)
Computes the Powers ratio for anterior atlanto-occipital dissociation from two distances on a lateral radiograph or CT.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Basion to the spinolaminar line of C1
- 44 mm
- Opisthion to the anterior arch of C1
- 40 mm
- Measured on
- Lateral radiograph
Result: Powers ratio 1.10: at or above 1, outside the normal range and consistent with anterior atlanto-occipital dissociation.
The tool opens with these values already filled in. Replace them with your own.
What you enter
- Basion to the spinolaminar line of C1 (BC)
- Opisthion to the anterior arch of C1 (OA)
- Measured on
- Basion-dens interval
How this is calculated
Citation
Powers B, Miller MD, Kramer RS, Martinez S, Gehweiler JA Jr. Traumatic anterior atlanto-occipital dislocation. Neurosurgery 1979;4(1):12-17. Method and normal values as tabulated in Rojas CA et al. AJNR Am J Neuroradiol 2007;28(9):1819-1823. Read the sources: Powers 1979 ↗, Rojas 2007 ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.