Bulging disc

A bulging disc is a spinal disc that extends beyond the edges of the vertebrae above and below it over a broad area. Radiologists use the term when the disc spreads past its normal boundary over 25% or more of its circumference. When a smaller, more localised part pushes out, under 25%, they call it a herniation instead (North American Spine Society). Each intervertebral disc has a tough outer ring, the annulus fibrosus, and in a bulge the disc as a whole spreads outwards past that edge.

“Bulge” describes a shape on a scan. The North American Spine Society notes that bulges reflect ordinary wear on the disc, are common in people with no pain and are less likely to be painful than herniations.

How common is a bulging disc?

Very common, including in people who feel fine:

• Lower back and whole spine. A review of 33 studies covering 3,110 people without symptoms found disc bulges in 30% of 20-year-olds, rising to 84% of 80-year-olds (Brinjikji et al., 2015).
• Neck. In MRI scans of 1,211 healthy volunteers aged 20 to 70, 87.6% had disc bulging. Even in their twenties, 73.3% of men and 78.0% of women had bulging discs. Compression of the spinal cord was rare, at 5.3%, and became more common after 50 (Nakashima et al., 2015).

That does not make a bulge meaningless. A second meta-analysis of adults aged 50 or younger found bulges were more common in people with low back pain than in people without, with an odds ratio of 7.54. The confidence interval ran from 1.28 to 44.56, which shows how uncertain the size of that link is (Brinjikji et al., 2015). A scan still can’t tell you whether a particular bulge is causing your pain. That is a clinical judgement, made with your symptoms and an examination. The age-related picture is covered under degenerative disc disease.

Bulging disc, herniated disc or slipped disc?

The words overlap in everyday use. The NHS uses “slipped disc”, also called a prolapsed or herniated disc, for a disc that bulges outwards, and notes that it hurts when it presses on nerves and that many people never know they have one (NHS). Radiology reports separate the broad bulge from the focal herniation. The two can also be confused: several small herniations can blend together and look like a bulge (North American Spine Society).

When disc material presses on a nerve root, pain, numbness or tingling can spread into an arm or a leg. This is radiculopathy, and in the leg it is usually called sciatica.

Does sitting cause a bulging disc?

The NHS lists ageing, sitting or driving for long periods, lifting heavy objects the wrong way, exercising too hard and being inactive or overweight among the things that can lead to a slipped disc, and advises not smoking (NHS). Its advice for recovery is to keep active with gentle exercise as soon as you can. For the desk side, see lower back pain from sitting.

Do you need a scan?

Usually not at first. NICE advises against routine imaging for low back pain with or without sciatica in non-specialist settings, and says specialists should consider it only if the result is likely to change management (NICE). The NHS says a slipped disc is usually diagnosed from symptoms, with an MRI if they don’t improve (NHS).

When to see a doctor

See a GP if painkillers aren’t helping, the pain isn’t improving after a few weeks, or it comes with a very high temperature, unexplained weight loss, a swelling in your back or pain that is worse at night. Call 999 or go to A&E if you have numbness around your bottom or genitals, cannot pee, lose feeling in one or both legs, cannot control when you pee or poo, or the pain began after a serious accident (NHS).