Reports name levels by the two vertebrae either side of a disc. Knowing the map makes the report far less opaque.
In more detail
- The spine runs C1–C7 in the neck (cervical), T1–T12 in the mid-back (thoracic), L1–L5 in the low back (lumbar), then the fused sacrum (S1–S5).
- ‘L4-L5’ means the disc between the fourth and fifth lumbar vertebrae. ‘L5-S1’ is the disc between the last lumbar vertebra and the sacrum — the lowest and most heavily loaded level, and the commonest site of herniation.
- Each nerve root supplies a predictable strip of skin and a predictable set of muscles, which is how the level is confirmed by examination.
What it means for you
This is why a good examination can often predict the scan. If your numbness is on the outer calf and the top of the foot and you cannot lift your toes, the L5 root is the suspect — and the scan is being used to confirm what the examination already suggested, not to go looking blindly.
Remember the general rule. Findings like this one are common in people with no pain at all, and become steadily more common with age. A finding on a report is not a diagnosis until someone has matched it to your symptoms and your examination. See understanding your MRI report.
Bring your scan and report in and we will go through it with you. Call (314) 310-5577 or request an appointment.
Common questions
Why are L4-L5 and L5-S1 mentioned so often?
They carry the most load and move the most, so they degenerate and herniate more than the levels above.
Hurt in an accident? Start here.
You do not need a lawyer, a police report or a referral to be seen. Bring your symptoms and we will work out the rest.
Monday–Friday, 8:00 a.m. – 4:00 p.m. Same-day appointments are often available for new accident and injury patients.