What causes chronic low back pain?

One of the most common questions I am asked is how can chronic pain happen? How can something still hurt after it has healed, that doesn't make sense? And it is difficult to understand because persistent low back pain is caused by a complex cascade of changes in our bodies; these changes take place in all our tissues but especially the spinal cord and brain.

Chronic Pain Syndrome

These changes cause the pain to become a problem in its own right – there may be no sign of underlying injury any more, or there may simply be signs of normal aging but the problem just goes on and on.

To understand how this cascade of change can happen you need to think of the body and your nervous system in a slightly different way.

Most of us are taught that pain = harm, but that is a better description of acute hurt. It is very hard to believe that pain does not always equal damage or harm when the symptoms continue and can be so unpleasant. Instead think of it as having a volume control.

  • Some systems of the body can turn the pain volume up and other systems can turn it down. If the bodies systems are focused on things that turn the volume up it will make problem persist long after healing has finished.

  • If the bodies systems for turning down the volume are not activated to oppose this volume the problem just gets louder and louder.

These volume controls to turn the noise up and down exist mainly in our brains and nervous system.

A combination of many different things lead to this problem but you might be surprised to learn that injury is not one of the most significant factors.

Does Pain = Harm?

Some people have severe lower back injuries, like fractures etc, fully recover and never have a problem again. Others may have a minor strain and end up with a lifetime of pain. You can't make sense or logic of chronic pain by thinking it is linked with the severity of an injury because the pain in itself is telling you nothing about how severely you may have hurt yourself – the two things are unrelated.

The biopsychosocial model

To better understand the causes of chronic lower back pain we need to touch on the bio-psychosocial model and theory. This video explains the three key areas:

In a nutshell:

  • Bio = biological or what is happening to your bodies tissues
  • Psycho= psychological, or what is happening with your thoughts
  • Social = sociological or what is happening in your world

Each one of these three things has a role to play in the volume controls for your pain. We have discussed that chronic symptoms often last long after injured tissue has healed so the 'bio' part of the equation – whilst important – is certainly not the whole story. What matters just as much is how you think and feel about your pain and the social situation you are in too.

If you want a bit more detail:

Biological structures that have been shown to give rise to back pain when provoked: (1)

  • Facet joint capsules
  • Ligaments
  • Intervertabral discs
  • Vertebrae
  • Nerves and their sleeves
  • Muscles

Psychological factors that play a role: (2)(3)

  • Anxiety
  • Increased body awareness
  • Fear and uncertainty
  • Anger and frustration
  • Depression
  • Beliefs about damage or disease
  • Fear of harm/hurt
  • Avoidance Beliefs about treatment

Social Factors:

  • Cultural beliefs and attitudes
  • The social context that the probe lm is felt in (an athlete for example may ignore symptoms when pushing the boundaries or performance but an unhappy worker may not)
  • The values we have about our role in society (needs and duties in relation to your role in society eg breadwinner)
  • Social support from partner, family, workmates etc
  • Compensation – financial or other

All these things combine to drive up the volume and if left unchecked physical changes occur in the brain and spinal cord in response to this. Not only is the volume louder but your body starts listening out more carefully for the sound and it sharpens its hearing. This means that the brain 'hears' pain signals much faster, for longer and at a lower threshold.

So in summary this problem is:
  • Complex, a cascade of changes
  • Sustained and worsened by biological, psychological and social factors
  • Not as much to do with tissue injury as many people expect
  • Can happen to anyone and is not 'all in your head'

Many more complex changes occur to magnify this response but I am not going to attempt to explain that here. Many medical professionals find it difficult enough to explain this phenomenon to someone who is actually face to face with them so a simple web page can't give you all the answers. I hope it has given you a glimpse into the many different things that can cause chronic lower back pain to become a problem.

I suggest taking a look at some of the references below or talking this over with your doctor.

Much more detailed information can be found in David Butlers excellent book Explain Pain and in these New Zealand Guidelines (4) referenced below



1. Merskey H, Bogduk N, International Association for the Study of Pain. Task Force on Taxonomy. Classification of chronic pain. Seattle: IASP Press; 1994.

2. Leeuw M, Goossens MEJ, Linton SJ, Crombez G, Boersma K, Vlaeyen J. The fear-avoidance model of musculoskeletal pain: Current state of scientific evidence. J BEHAV MED. 2007;30(1):77–94.

3. Gordon Waddell. The Back Pain Revolution. Churchill Livingstone; 1998.

4. Kendall, N A S, Linton, S J & Main, C J. Guide to Assessing Psycho-social Yellow Flags in Acute Low Back Pain: Risk Factors for Long-Term Disability and Work Loss. Accident Compensation Corporation and the New Zealand Guidelines Group, Wellington, New Zealand. [Internet]. 1997; Available from: http://www.acc.co.nz/PRD_EXT_CSMP/groups/external_ip/documents/internet/wcm002131.pdf





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