Understanding pain
Discs, herniated disks and sciatica
"Slipped disc", "bulging disc", "trapped nerve" and "sciatica" are some of the most used and least understood words in conversations about backs. This page explains what the discs are, what happens when one is said to be herniated, and what sciatica actually describes.
What the discs are
Between the bones of the spine sit the intervertebral discs. MedlinePlus, in its page on a herniated disk, describes them as soft disks filled with a jelly-like substance that cushion the vertebrae and keep them in place. Each disc has a tougher outer ring and a softer centre, a little like a jam doughnut with a firm crust.
The discs let the spine bend and twist while spreading the forces of walking, running and lifting. The National Institute of Arthritis and Musculoskeletal and Skin Diseases describes them as cushion-like pads that act like shock absorbers and spacers for the spine. They have a limited blood supply, which is one reason they change slowly over a lifetime.
How discs change with age
With age, discs tend to lose water, become less springy and lose some height. MedlinePlus explains that as the disks break down, or degenerate, they lose their cushioning ability. OrthoInfo's page on low back pain adds that small tears in the outer part of the disc sometimes occur with ageing, and that some people with disc tears have no pain at all while others have pain that lasts a long time.
That last point is worth dwelling on. Changes in the discs are very common, and many of them cause no symptoms. A scan that shows "degeneration" is often describing ordinary ageing rather than the cause of a particular ache, which is why a provider will weigh a scan against your symptoms and examination rather than reading it on its own.
What "herniated", "bulging" and "slipped" mean
A herniated disc is one in which the softer centre pushes through a weak spot or tear in the outer ring. MedlinePlus describes it as a disk that ruptures, allowing the jelly-like centre to leak and irritate the nearby nerves, which can cause sciatica or back pain. A bulging disc is usually used to describe a disc whose outer ring sticks out more widely than usual without the centre breaking through. "Slipped disc" is a popular phrase for the same group of problems, but it is misleading: discs are firmly attached to the bones above and below and do not slide out of place.
What sciatica describes
Sciatica is not a diagnosis in itself. MedlinePlus explains on its sciatica page that it is a symptom of a problem with the sciatic nerve, the largest nerve in the body, which provides feeling to the back of the thigh, part of the lower leg and the sole of the foot. When the nerve or the roots that form it are irritated, people feel pain, weakness, numbness or tingling that can travel from the lower back through the buttock and down the leg.
The same page lists causes that include a ruptured disc, a narrowing of the spinal canal that puts pressure on the nerve, called spinal stenosis, and an injury such as a pelvic fracture, and notes that in many cases no cause can be found. It also notes that sciatica sometimes goes away on its own, and that treatment, when needed, depends on the cause.
Leg pain and back pain are different signals
Pain that stays in the back and pain that runs down a leg below the knee are described differently by providers, and both MedlinePlus and OrthoInfo treat spreading leg pain, numbness and weakness as signs to take seriously. Loss of bladder or bowel control, or numbness or weakness in the buttocks, thighs or legs, is a reason to contact a provider right away.
Get it checked promptly
Some back and neck pain needs prompt medical care rather than waiting it out: pain that follows a fall, a crash or a hard blow; pain that comes with numbness, tingling or weakness in an arm or a leg; any loss of bladder or bowel control; pain that comes with a fever; and pain that is severe or keeps getting worse. The fuller list, drawn from MedlinePlus and the American Academy of Orthopaedic Surgeons, is on When to see a doctor.
Questions worth asking
If you have been told you have a disc problem or sciatica, it is reasonable to ask what exactly was found, whether it matches your symptoms, what everyday activity is sensible for now, and what signs should bring you back sooner. MedlinePlus notes that a herniated disk is usually diagnosed with a physical exam and, sometimes, imaging tests, and that the treatments providers consider range from rest and medicines to physical therapy and, sometimes, surgery. Those are decisions to make with a provider who knows your situation. The before a first visit page has more questions, and the lower back anatomy page shows where the discs and nerve roots sit.