Discs sit in between your vertebrae all the way up and down your spine. Their primary function is to act as a shock absorber, as their springy structure allows them to compress under load and take on forces which would damage the inflexible bone of the vertebrae.
The second function of your discs is to facilitate movement. Out to the side of each disc are two joints called facet joints, which work together with your disc so that two vertebrae can slide around each other. Each facet joint is uniquely shaped to allow a specific range of motion, all combining together to create the highly flexible and sturdy spinal column.
These two functions are clearly represented in the structure of a disc, which is made up of two distinct layers: a tough outer layer of fibrous tissue called the annulus, and a gel-like inner layer called the nucleus.
If you were to zoom in on the annulus, you would see it’s made up of criss-crossing fibres arranged in onion layers that allow a degree of movement while maintaining tension, much like you’d see in the fibres of a rope.
The tough annulus also holds together the two vertebrae on either side and forms a barrier to contain the highly compressible nucleus, which gives the disc its shock absorbing properties.
How does a disc get injured?
Because the nucleus of each disc contains a lot of water, they gradually shrink in size throughout the day as the body dehydrates slightly, then fill back up again at night, which is why you’re slightly taller and more likely to feel stiff in the morning.
Water absorption in the nucleus also slows as we age, one of the many factors that leads to natural disc degeneration. The drier and flatter your discs, the less protection they’ll provide for the vertebrae on either side, which can cause discomfort, degenerative arthritis and/or injury.
Discs – either through gradual wear and tear or acute injury – can also become prolapsed. This is when a weakened or even torn annulus is no longer able to properly contain the nucleus within, causing the disc to bulge and become misshapen.
A prolapsed disc is the proper term for a slipped disc, which is a term you won’t catch us using because a disc is firmly attached to the vertebrae on either side and simply cannot slip. Many misconceptions surrounding discs that frustrate us physios stem from this very common misnomer.
It’s entirely possible for a disc bulge to go entirely unnoticed. In fact, a study of people with healthy backs over the age of 35 found that 60% of them had disc bulges that presented no symptoms at all. They’re often simply a natural and very common part of ageing, and far from the spinal death sentence they’re often perceived to be by worried patients.
When a prolapsed disc does cause problems it is when the bulge presses against the nerves in your spine leading to sciatica, which can cause pain or numbness in the hips, legs or buttocks. In extreme cases, a prolapsed disc can push on the spinal cord, but this is a medical emergency that would be impossible not to notice.
Are my discs the cause of my back pain?
While degenerated discs can exacerbate back problems such as arthritis, unless you have a symptomatic prolapsed disc, it’s unlikely that your discs are to blame for your back pain. Unfortunately, because of their prevalence on MRI scans, discs are often blamed for back problems even if the disc degeneration is entirely asymptomatic.
So what is the real cause for back pain, and how can you look after your spine? Click here for my next blog with the answers.
If you have any questions feel free to get in touch with me at firstname.lastname@example.org or book an appointment by calling 0207 937 1628 .
Kam Sowman BSc (Physio) MCSP MHCP
Musculoskeletal and Sports Physiotherapist