Which spine type is your scan?
Got a side-view X-ray or MRI of your lower back? Tap four corners on two bones and get a best guess at your Roussouly spine type.
A best guess, not a diagnosis. It uses the published X-ray cut-offs, but a few pixels in a tap can change the answer, and MRIs are taken lying down. Ask your clinician if the result matters to your care.
A side view of the lower spine
An X-ray (best if taken standing) or the middle slice of an MRI, showing L5 and the top of the sacrum clearly.
Upright, not tilted
A screenshot is best. If you photograph a screen, hold the phone square to it so the image isn’t tilted.
Top of S1, top of L5
The front and back corners of the top of the sacrum, then the same on the vertebra above. Zoom in for accuracy.
- Front corner of the top of the sacrum (S1)
- Back corner of the top of the sacrum
- Front corner of the top of L5
- Back corner of the top of L5
Your scan stays on your device
The check runs entirely in your browser. Your image isn’t uploaded, sent or stored anywhere, and it’s gone when you close the page.
No scan to hand? Try it on my own MRIs: lower back and upper back, lying down.
Example: my own MRI scans, taken lying down, with personal details cropped out.
Zoom in, scroll to the bottom of the spine, and tap each corner. On a computer you can drag a point to adjust it.
How the guess is made
Step 1, sacral slope. Roussouly’s classification (Roussouly et al., Spine, 2005) splits spines by the angle of the top of the sacrum on a standing X-ray: above 45° is Type 4, 35–45° is Type 3, and below 35° is Type 1 or Type 2.
Step 2, Type 1 or Type 2. Both have a low sacral slope. A 2026 study of 102 adults found the angle between L5 and S1 separated them best: 19° or less pointed to Type 2, more than 19° to Type 1 (Compagnone et al., European Spine Journal, 2026). This check measures it from the top of L5 to the top of S1. That study’s exact method may differ, so treat results close to 19° as uncertain.
Optional: the upper back. If your scan shows the whole spine, you can add T4 and T12 to measure the rounding of the upper back. Roussouly’s types are set by the sacrum, so this doesn’t override a clear result. It only acts as a tie-break when the sacral slope sits within 3° of the 35° line: a flat upper back (under 20°) with a small L5–S1 angle tips the guess to Type 2. That tie-break is my own rule, not a published one.
MRI scans are taken lying down, when the lower back usually curves less than when standing. The type from an MRI is a rougher guess than from a standing X-ray.
No scan?
Stand side-on to a mirror or ask someone to photograph you, and compare the overall shape of your back with the four types. A flat back has little hollow in the lower back and little rounding in the upper back.