Alternative DEXA Scanning for Patients Unable to Lie Flat
If a patient cannot lie flat for standard lumbar spine and hip DEXA, perform a forearm DEXA scan of the non-dominant arm (distal one-third radius). This is the guideline-recommended alternative when standard positioning is not possible 1.
Primary Alternative: Forearm DEXA
The most recent 2025 European guidelines explicitly state that forearm scanning should be considered when patients cannot be positioned comfortably on the table 1. This addresses your exact clinical scenario.
When to Use Forearm DEXA:
- Patient cannot mount or be positioned comfortably on the table
- Patient exceeds weight limit of scanner table (120-150 kg depending on scanner type)
- Lumbar spine/hip contain artifacts limiting interpretation (fractures, hardware, severe degenerative changes)
- Large discordance (>1 T-score unit) between lumbar and hip scans
- Hyperparathyroidism diagnosis (forearm should always be performed) 1
Technical Considerations:
- Scan the non-dominant arm at the distal one-third radius
- Patient can be in sitting position with arm on table (though supine may reduce movement artifacts if tolerable) 1
- No hardware, fusion, osteoarthritis, or fractures should be present at the site
- The radius and ulna should be parallel to the short axis of the scanning table 1
Secondary Alternatives (When DEXA is Completely Unavailable)
If even forearm DEXA positioning is impossible, consider these alternatives based on guideline ratings 2:
Quantitative CT (QCT) - Rating 6-7
- Can be performed with patient in various positions
- Higher radiation exposure than DEXA (☢☢☢ vs ☢)
- More accurate than DEXA in patients with spinal degeneration 2
- Can assess lumbar spine, hip, or tibia
Quantitative Ultrasound (QUS) of Calcaneus - Rating 2
- Non-ionizing radiation
- Small, portable units
- Critical limitation: Does not measure BMD directly, so WHO T-score criteria cannot be applied 2
- Generally not appropriate for clinical decision-making per guidelines
Important Caveats
The forearm DEXA is not equivalent to spine/hip measurements - it measures predominantly cortical bone at a peripheral site. However, it provides valid T-scores using WHO criteria and can guide treatment decisions when central sites are unavailable 2, 1.
Do not use peripheral QCT (pQCT) or single x-ray absorptiometry (SXA) - these receive low appropriateness ratings (2-3) in current guidelines and are not widely used in practice 2.
Opportunistic CT screening (measuring Hounsfield units from existing CT scans) is emerging but not yet guideline-endorsed as a replacement for DEXA, though research shows promise 3, 4, 5. This would require a CT scan already being performed for other indications.
The 2025 guidelines emphasize that consistent positioning at the same site for longitudinal measurements is critical 1, so once you establish forearm DEXA as the monitoring site, continue using it for all follow-up scans.