Disc injuries go by many different names; A slipped disc, bulging disc, herniated disc, disc prolapse, disc protrusion, or degenerative disc disease.
Whatever term you’ve heard, disc-related issues are very common.
In fact, a large percentage of the population have disc bulges without ever knowing it, because not all disc bulges cause pain. This is an important point, and one we’ll return to later.
This blog post is Part 1 of a two-part series.
In this post, I’ll explain:
In Part 2, I’ll cover diagnosis, treatment options, and practical things you can do at home to support recovery and reduce the risk of future disc issues.
Even if you’ve never been diagnosed with a disc injury, understanding how they develop can help you prevent problems before they start.
Note: if you want some quick firs answers, head to the FAQ section at the end of this blog.
Related: Why does pain sometimes show up later?
Whatever term you’ve heard, disc-related issues are very common.
In fact, a large percentage of the population have disc bulges without ever knowing it, because not all disc bulges cause pain. This is an important point, and one we’ll return to later.
This blog post is Part 1 of a two-part series.
In this post, I’ll explain:
- What a spinal disc is
- How disc injuries occur
- Why many disc bulges don’t cause pain
- The range of symptoms disc injuries can cause
In Part 2, I’ll cover diagnosis, treatment options, and practical things you can do at home to support recovery and reduce the risk of future disc issues.
Even if you’ve never been diagnosed with a disc injury, understanding how they develop can help you prevent problems before they start.
Note: if you want some quick firs answers, head to the FAQ section at the end of this blog.
Related: Why does pain sometimes show up later?
The Anatomy of a Spinal Disc
A spinal disc is technically called an intervertebral disc, because it sits between two vertebrae in your spine.
Its primary role is to absorb shock and allow controlled movement between spinal segments.
Discs are firmly attached to the vertebrae above and below by very strong fibrous tissue (called Sharpey’s Fibres). In fact, cadaver studies have shown that under extreme load, the vertebrae will fracture before these fibres break. This is why the term “slipped disc” is not anatomically accurate, discs don’t actually slip.
The disc has two main parts:
As we age, the nucleus pulposus gradually loses water content and becomes less elastic, which can reduce its ability to absorb load effectively.
Its primary role is to absorb shock and allow controlled movement between spinal segments.
Discs are firmly attached to the vertebrae above and below by very strong fibrous tissue (called Sharpey’s Fibres). In fact, cadaver studies have shown that under extreme load, the vertebrae will fracture before these fibres break. This is why the term “slipped disc” is not anatomically accurate, discs don’t actually slip.
The disc has two main parts:
- Annulus fibrosus – a tough, fibrous outer layer
- Nucleus pulposus – a gel-like centre that gives the disc its shock-absorbing properties
As we age, the nucleus pulposus gradually loses water content and becomes less elastic, which can reduce its ability to absorb load effectively.
Disc Nutrition, Movement, and Fluid Changes
Spinal discs have very little direct blood supply. Instead, they rely on movement of the spine to absorb nutrients, a process known as imbibition.
This is one of the reasons regular movement is so important for spinal health.
Spinal discs also absorb fluid overnight, which means they are at their largest and most hydrated first thing in the morning. This is why:
Another key point: The inner part of the disc has no nerve supply. Only the outer third of the annulus fibrosus contains pain-sensitive nerve fibres. This explains why many people can have disc changes without experiencing pain.
This is one of the reasons regular movement is so important for spinal health.
Spinal discs also absorb fluid overnight, which means they are at their largest and most hydrated first thing in the morning. This is why:
- You are slightly taller in the morning than at night
- Your spine may be more vulnerable early in the day
Another key point: The inner part of the disc has no nerve supply. Only the outer third of the annulus fibrosus contains pain-sensitive nerve fibres. This explains why many people can have disc changes without experiencing pain.
How a Disc Injury Occurs
Disc injuries usually develop gradually over time, rather than from a single event.
Repeated poor movement patterns, such as bending through the lower back instead of the hips, prolonged slouched sitting, or poor lifting technique, can cause small cracks to form in the outer fibres of the disc.
These cracks allow the nucleus pulposus to slowly migrate toward the edge of the disc.
Because the inner disc has no nerve supply, this process can occur without symptoms for quite some time.
Once the outer nerve fibres are irritated, pain can develop. Over time, these nerve fibres may grow deeper into the disc, meaning less and less stress is required to trigger symptoms.
If you’ve had back problems before and noticed that it takes less to aggravate your back now than it used to, this is often why.
As the disc material moves outward, a disc bulge can form. In more severe cases, you can get a disc protrusion and an extrusion when some of the nucleus makes its way to the edge of the disc (see image below). Depending on its size and location, it may irritate nearby structures such as spinal nerves, and in more severe cases, the spinal cord itself.
Occasionally, disc material can break free and move into the spinal canal. This is known as a disc sequestration.
Repeated poor movement patterns, such as bending through the lower back instead of the hips, prolonged slouched sitting, or poor lifting technique, can cause small cracks to form in the outer fibres of the disc.
These cracks allow the nucleus pulposus to slowly migrate toward the edge of the disc.
Because the inner disc has no nerve supply, this process can occur without symptoms for quite some time.
Once the outer nerve fibres are irritated, pain can develop. Over time, these nerve fibres may grow deeper into the disc, meaning less and less stress is required to trigger symptoms.
If you’ve had back problems before and noticed that it takes less to aggravate your back now than it used to, this is often why.
As the disc material moves outward, a disc bulge can form. In more severe cases, you can get a disc protrusion and an extrusion when some of the nucleus makes its way to the edge of the disc (see image below). Depending on its size and location, it may irritate nearby structures such as spinal nerves, and in more severe cases, the spinal cord itself.
Occasionally, disc material can break free and move into the spinal canal. This is known as a disc sequestration.
Not All Disc Bulges Cause Pain
If you take away one key point from this post, this is it.
A study published in the American Journal of Neuroradiology looked at people with no back pain at all and found disc bulges were extremely common. For example:
This means that finding a disc bulge on imaging does not automatically explain someone’s symptoms. Pain depends on where the disc bulge is and what structures it affects.
The chart below shows the full findings from the study above. I find this pretty interesting.
A study published in the American Journal of Neuroradiology looked at people with no back pain at all and found disc bulges were extremely common. For example:
- 50% of people in their 40s had disc bulges, without pain.
- 60% of people in their 50s had disc bulges, without pain.
- 69% of people in their 60shad disc bulges, without pain.
This means that finding a disc bulge on imaging does not automatically explain someone’s symptoms. Pain depends on where the disc bulge is and what structures it affects.
The chart below shows the full findings from the study above. I find this pretty interesting.
The Disc Bulge Continuum
I like to explain disc injuries using what I call the disc bulge continuum.
Most people sit somewhere in between, and knowing where you fall on this continuum is key to choosing the right treatment approach.
- At one end: disc bulges with no pain or symptoms
- In the middle: disc bulges causing localised back or neck pain
- At the far end: disc bulges that irritate or compress nerves, causing symptoms such as sciatica, arm pain, weakness, or numbness
Most people sit somewhere in between, and knowing where you fall on this continuum is key to choosing the right treatment approach.
Where Disc Injuries Occur & Who Is at Risk
Disc injuries most commonly affect the lower back (lumbar spine), but they can also occur in the neck and upper back.
They are most common in adults aged 30–50, though they can occur at any age, including teenagers. Poor posture, prolonged sitting, and reduced movement are increasingly contributing factors in younger people.
They are most common in adults aged 30–50, though they can occur at any age, including teenagers. Poor posture, prolonged sitting, and reduced movement are increasingly contributing factors in younger people.
Common Causes of Disc Injuries
Disc injuries can occur due to:
Related: A surprising factor for lower back disc injuries
- Sudden trauma or force
- Repetitive poor movement patterns over time
- Prolonged poor posture (especially sustained spinal flexion)
- Weakness or poor coordination of supporting muscles
- In some cases, there is no clear triggering event at all
Related: A surprising factor for lower back disc injuries
Degenerative Disc Changes
As part of normal ageing, discs lose water content and elasticity. Small tears can develop in the outer fibres, which may cause pain.
Degenerative changes are often associated with bone spurs (osteophytes), which can further irritate surrounding tissues.
Degeneration does not automatically mean pain, but it can increase vulnerability if combined with poor movement habits.
Degenerative changes are often associated with bone spurs (osteophytes), which can further irritate surrounding tissues.
Degeneration does not automatically mean pain, but it can increase vulnerability if combined with poor movement habits.
Symptoms of a Disc Injury
Disc injuries can present in several ways:
The symptoms all depend on where the bulge is located and what structures (if any) are involved.
Symptoms are often aggravated by bending forward, twisting, coughing, sneezing, straining, or prolonged sitting.
Important:
If a disc injury causes changes in bowel or bladder control, this is a medical emergency and requires immediate assessment.
Related: How to sit with a L4/L5 or L5/S1 disc bulge
- No pain at all
- Localised pain and stiffness (acute or chronic): Muscular spasm, trigger points, aches, antalgic lean
- Nerve pain: radiating pain, numbness, tingling, or weakness in the arms or legs (e.g. sciatica)
The symptoms all depend on where the bulge is located and what structures (if any) are involved.
Symptoms are often aggravated by bending forward, twisting, coughing, sneezing, straining, or prolonged sitting.
Important:
If a disc injury causes changes in bowel or bladder control, this is a medical emergency and requires immediate assessment.
Related: How to sit with a L4/L5 or L5/S1 disc bulge
Where to From Here?
Hopefully, this post has helped clarify:
In Part 2, I’ll cover how disc injuries are diagnosed, treatment options, and practical things you can do at home to support recovery and prevent future flare-ups. So, make sure you keep an eye out for that post.
If you’d like your back assessed or have questions about disc injuries, you can book an appointment online here or contact the clinic, I’m always happy to help.
See you for part 2.
- What disc injuries are
- How they develop
- Why disc bulges don’t always cause pain
In Part 2, I’ll cover how disc injuries are diagnosed, treatment options, and practical things you can do at home to support recovery and prevent future flare-ups. So, make sure you keep an eye out for that post.
If you’d like your back assessed or have questions about disc injuries, you can book an appointment online here or contact the clinic, I’m always happy to help.
See you for part 2.
References
Brinjikji et al (2015) Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. American Journal of Neuroradiology
FAQs for Part 1: Understanding Disc Bulges
What is a disc bulge?
A disc bulge occurs when the soft centre of a spinal disc pushes outward against the tougher outer fibres. Disc bulges usually develop gradually over time rather than from a single injury.
Is a disc bulge the same as a slipped disc?
No. The term “slipped disc” is inaccurate. Spinal discs do not slip out of place. A disc bulge refers to a change in the disc’s shape, not movement of the disc itself.
Do all disc bulges cause pain?
No. Many people have disc bulges without any pain or symptoms. Research shows disc bulges are very common in people with no back pain, especially as we age.
Why can someone have a disc bulge without pain?
The inner part of the disc has no pain-sensitive nerve supply. Pain usually only occurs if the outer fibres of the disc or nearby structures, such as nerves, become irritated.
What symptoms can a disc bulge cause?
Symptoms can range from no pain at all, to localised back or neck pain, to nerve-related symptoms such as sciatica, numbness, tingling, or weakness in the arms or legs. I often refer to this the disc bulge continuum
Does the size of a disc bulge determine how serious it is?
No. The size of a disc bulge does not reliably predict pain or symptoms. What matters more is whether surrounding nerves or tissues are being irritated.
Where do disc bulges most commonly occur?
Disc bulges most commonly affect the lower back (lumbar spine). The most common levels are L4/5 and L5/S1. However, they can also occur in the neck (cervical spine) and upper back (thoracic spine as well).
RSS Feed
