Each disc between the bones of the spine has a tough outer wall of layered fibres around a softer, gel-like centre. In a bulging disc, the wall spreads outward past the edges of the bones above and below, around a wide stretch of the disc's rim, rather like a tyre that is low on air. In a herniated disc, part of the soft centre pushes through a weak point or tear in the wall, so the change is concentrated in one place. Slipped disc is the everyday name for both.
A scan report may call a herniation a protrusion or an extrusion
Those words describe the shape of the material that has pushed out. A protrusion is broadest where it leaves the disc. In an extrusion, the part beyond the disc is wider than the narrow neck joining it back, and a piece that has broken away from the disc altogether may be called a sequestration. Each level of the spine gets its own line on the report, so one disc can be described as bulging and another as herniated.
Disc bulges are common on scans of people with no pain at all
A 2015 review in the American Journal of Neuroradiology, pooling CT and MRI findings from 3,110 people without back pain, estimated that disc bulges show up in 30% of 20-year-olds, rising to 84% of 80-year-olds, and protrusions in 29%, rising to 43%. Its authors concluded that many of these changes are likely part of normal ageing and unrelated to pain, and that scan findings have to be read alongside a person's symptoms and examination. A bulge on a report can be real and still have nothing to do with the ache that sent you for the scan. Disc problems are one of the seven common causes of back pain, and a disc change on a scan does not rule out the other six.
Pain below the knee, numbness or weakness suggest a nerve is involved
Pain from a disc itself tends to stay in the lower back and buttock, sometimes reaching the thigh. When disc material presses on or inflames a nerve root, the leg often hurts more than the back, and the pain runs below the knee, sometimes into the foot and toes. Pins and needles or numbness can follow the same path, and weakness may show up as a foot that catches on steps. Coughing or sneezing can sharpen it, and some people feel it most after a long spell of sitting, at a laptop or on a scooter. A disc in the neck can send the same kind of symptoms down an arm and into the hand. How the clinic assesses pain that travels is set out on our sciatica and nerve pain page.
A doctor diagnoses the disc, while The Sync measures and supports movement
Telling a bulge from a herniation, and deciding whether either one explains your symptoms, is a medical diagnosis made from an examination and, when it is needed, a scan. The Sync does not diagnose, prescribe medication, inject, operate, or order or read scans.
Care here starts with assessment and measurement. SpinalSync tests each segment of the spine on its own, with the readings on a screen as they are taken, and MyoSync works with the fascia and soft tissue around it. Measuring again on later visits shows whether anything has changed, and the aim is comfort and easier movement alongside whatever a doctor has advised. If the assessment turns up something that belongs with a doctor, a Sync specialist says so before anything else happens. The systems are set out on our methods page, and disc problems sit with the other spinal conditions on our conditions page.
Common questions about bulging and herniated discs
Not necessarily. Either one can press on a nerve, and either one can show up on a scan without causing any symptoms, so the label on its own says little about your pain.
Not directly. An X-ray shows bone rather than disc tissue, so at most it hints at a disc problem, for example where the gap between two vertebrae has narrowed. MRI is the scan usually used to see a bulge or a herniation.
Mostly, yes. The NHS uses slipped, prolapsed and herniated disc as names for the same problem, and slipped disc often gets used for a bulge as well. Nothing actually slips, because each disc is attached to the bones above and below it.
No. Explaining a scan is a doctor's job. We assess, measure, monitor change, and support comfort and movement alongside what your doctor advises.
Written by the Aphyx Content team, reviewed by the clinical team at The Sync. Published 24 September 2026. Last updated 24 September 2026.