🧠 Craniocervical Junction Measurements (ADI / PADI / Powers / BDI / Basilar Invagination)
UseCraniocervical junction imaging: lateral cervical radiographs and sagittal CT — trauma, rheumatoid and congen…
SourcePowers B, et al. Traumatic anterior atlanto-occipital dislocation. Neurosurgery 1979;4:12-17
This-shift next steps
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Methodology · worked example, guidelines & full notes
Lateral cervical radiograph or sagittal CT.
When to use
Craniocervical junction imaging: lateral cervical radiographs and sagittal CT — trauma, rheumatoid and congenital craniocervical assessment.
How it works
ADI (adult) ≤ 3 mm: normal ADI (adult) 3–5 mm: transverse ligament injury / atlantoaxial instability likely ADI (adult) > 5 mm: transverse and alar ligament injury, marked instability (RA > 9 mm: consider surgery) ADI (child) ≤ 5 mm: normal in children ADI (child) > 5 mm: abnormal, atlantoaxial instability PADI < 14 mm: high cord-compression risk (surgical threshold in RA) PADI ≥ 14 mm: adequate space for the cord Powers ratio < 1: normal Powers ratio ≥ 1: anterior atlanto-occipital dislocation BDI (radiograph) ≤ 12 mm: normal (Harris rule of 12) BDI (radiograph) > 12 mm: possible atlanto-occipital dislocation BDI (CT) ≤ 8.5 mm: normal on CT BDI (CT) > 8.5 mm: abnormal, possible atlanto-occipital dislocation Dens tip above McGregor's line ≤ 4.5 mm: normal Dens tip above McGregor's line > 4.5 mm: basilar invagination
Key points
- Lateral cervical radiograph or sagittal CT.
- Each value is graded against published reference ranges.
- Measurement technique and positioning change the numbers — compare like with like on follow-up.
- Part of the YuanDoctor MSK measurement topic.
References
- Powers B, et al. Traumatic anterior atlanto-occipital dislocation. Neurosurgery 1979;4:12-17
- Harris JH Jr, et al. Radiologic diagnosis of traumatic occipitovertebral dissociation. AJR 1994;162:881-886
- Rojas CA, et al. Reassessment of the craniocervical junction: normal values on CT. AJNR 2007;28:1819-1823
- Boden SD, et al. Rheumatoid arthritis of the cervical spine: posterior atlanto-odontoid interval. J Bone Joint Surg Am 1993;75:1282-1297
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Population | Adult |
|---|---|
| BDI modality | Radiograph |
| Powers: basion → posterior C1 arch | 30 mm |
| Powers: opisthion → anterior C1 arch | 38 mm |
| ADI (adult) | 2.5 mm |
| PADI | 16 mm |
| BDI (radiograph) | 8 mm |
| Dens tip above McGregor's line | 3 mm |
→ADI (adult)2.5mm
- ADI (adult)：2.5 mm → ≤ 3 mm: normal
- PADI：16 mm → ≥ 14 mm: adequate space for the cord
- Powers ratio：0.79 → < 1: normal
| Population | Child (≤ ~8 y) |
|---|---|
| BDI modality | CT |
| Powers: basion → posterior C1 arch | 30 mm |
| Powers: opisthion → anterior C1 arch | 38 mm |
| ADI (child) | 4 mm |
| PADI | 16 mm |
| BDI (CT) | 6 mm |
| Dens tip above McGregor's line | 3 mm |
→ADI (child)4mm
- ADI (child)：4 mm → ≤ 5 mm: normal in children
- PADI：16 mm → ≥ 14 mm: adequate space for the cord
- Powers ratio：0.79 → < 1: normal
Verification & sources · governance
FAQ
Frequently asked questions
- What are the limits and cautions when using Craniocervical Junction Measurements (ADI / PADI / Powers / BDI / Basilar Invagination)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- Does Craniocervical Junction Measurements (ADI / PADI / Powers / BDI / Basilar Invagination) upload patient data? Where is it calculated?
- Calculation runs locally in the browser; inputs and results are not uploaded. For licensed clinicians only; interpret with history, investigations and local protocols — not a diagnosis or prescription.
- How is Craniocervical Junction Measurements (ADI / PADI / Powers / BDI / Basilar Invagination) calculated in practice? Can you show a worked example?
- Inputs: Population Adult, BDI modality Radiograph, Powers: basion → posterior C1 arch 30 mm, Powers: opisthion → anterior C1 arch 38 mm, ADI (adult) 2.5 mm, PADI 16 mm, BDI (radiograph) 8 mm, Dens tip above McGregor's line 3 mm → Result: ADI (adult) 2.5 mm（ADI (adult): 2.5 mm → ≤ 3 mm: normal, PADI: 16 mm → ≥ 14 mm: adequate space for the cord, Powers ratio: 0.79 → < 1: normal） Inputs: Population Child (≤ ~8 y), BDI modality CT, Powers: basion → posterior C1 arch 30 mm, Powers: opisthion → anterior C1 arch 38 mm, ADI (child) 4 mm, PADI 16 mm, BDI (CT) 6 mm, Dens tip above McGregor's line 3 mm → Result: ADI (child) 4 mm（ADI (child): 4 mm → ≤ 5 mm: normal in children, PADI: 16 mm → ≥ 14 mm: adequate space for the cord, Powers ratio: 0.79 → < 1: normal）