Fear, disability, chickens and eggs

The Fear Avoidance Model (FAM) has been a big player in the recent history of chronic pain research and clinical practice. Simply put, the premise of the model is that in the acute stage of an injury or painful event, the presence of fear and catastrophic beliefs regarding the meaning of pain or the possible consequences of activity leads to hypervigilance to symptoms, avoidance of activity and subsequent disuse, depression and disability which self-perpetuates in a vicious cycle. As a model it makes good sense, and is easy to understand.

Chicken or egg

But a model doesn’t stand or fall on plausibility alone (or at least it shouldn’t). What we need to know is given the predictions of the model, what do the data tell us? A new systematic review in the Journal of Pain investigates an aspect of that. Emily Zale and colleagues systematically reviewed cross-sectional studies and performed a meta-analysis of the relationship between pain-related fear and disability in populations with pain. This approach gives us the most robust estimate of the relationship and tells us something about its consistency. They included studies that involved 46 independent samples and 9,579 participants and demonstrated a robust moderate to strong correlation between pain-related fear and disability that was consistent regardless of the type of pain, the duration of pain or the demographics of the group. So we can, and they do, happily conclude that the relationship exists. They discuss that the results are largely consistent with the FAM. Which technically they are, but there is a fairly hefty chicken-&-egg style “but”.

The FAM has it that fear is a driver of disability and a causal agent in the path to chronic disability and pain. As Zale’s group acknowledge cross-sectional studies do not allow conclusions of causality, and for good reason. Sure, fear might drive your disability but equally severe disabling pain might make you fearful. It would be rather odd if it did not. Plainly, regardless of whether or not the fear avoidance model is correct it would be surprising if these variables were not cosy with each other. The only way to come close to interrogating the key question – is fear an important driver of disability?, is through prospective studies. Get people in the very acute phase, measure the fear and follow them over time to see who develops chronic disability.

I trawled through much of this literature for one of my PhD chapters, specifically in low back pain. The evidence was wildly inconsistent, with fear related variables appearing and disappearing as a predictor from the significant results of a number of prospective studies. It could be big, small, or simply not there and the more robust the study,  the smaller the effect. Some of this inconsistency is doubtless the result of varying methods but together it does not offer strong support for the model.

There is evidence there, but it is on the shaky side.  In a recent commentary Lorimer mused that perhaps the fear avoidance model has not lived up to expectations. The time has probably not come to discard it but we need to recognise that it is far from proven that fear is an important player in the development of chronic disability. So what do we know? This new review confirms that fear and disability regularly enjoy each other’s company. But whether one drives the other, or they are just passengers in the same bargain bucket is not so clear.

Neil O’Connell

Neil O'ConnellAs well as writing for Body in Mind, Dr Neil O’Connell, (PhD, not MD) is a researcher in the Centre for Research in Rehabilitation, Brunel University, West London, UK. He divides his time between research and training new physiotherapists and previously worked extensively as a musculoskeletal physiotherapist.
He also tweets! @NeilOConnell
Neil’s main research interests are chronic low back pain and chronic pain more broadly with a focus on evidence based practice. He has conducted numerous systematic reviews including some for the Cochrane Collaboration. He also makes a mean Yorkshire pudding despite being a child of Essex.
Link to Neil’s published research here. Downloadable PDFs here.


Zale EL, Lange KL, Fields SA, & Ditre JW (2013). The Relation Between Pain-Related Fear and Disability: A Meta-Analysis. J Pain PMID: 23850095


  1. Guido Van Ryssegem says

    Steve, interesting topic you brought forward. Related to it you will find the following an interesting relationship: Although there are very practical reasons to fear heights, babies don’t become afraid until about six weeks after they learn to crawl. To find out what causes this shift, researchers at the University of California, Berkeley put babies who couldn’t yet crawl into go-carts they could control with joysticks. After three weeks, the babies who drove showed anxiety after being confronted with a steep drop, while their non-driving peers remained fearless. This research suggests that moving around in space–by crawling, walking, or even go-carting–conditions our brains to take in more information from our peripheral visual field. This would also explain why you don’t feel fear when when viewing the earth from a small plane window, which limits your peripheral vision. Read more here: http://bit.ly/14klI68

    Related to the above article, when I work with my patients that exhibit fear to step or jump off a stool (a test often used to identify if postoperative ACL patients are ready to start jogging), I limit their visual field by asking them to crop their hands together like as if holding a grapefruit. By them looking through the relatively small opening between their hands (limiting their visual field) they often exhibit an improved and non-fearful stepping or jumping down movement pattern that I actually measure using slow video – time-to contact with the floor when they land and well as knee and ankle range of motion immediately normalize. Fascinating how the role of perception/attention can immediately change movement and performance.

  2. Neil Pearson says

    Good point Steve.
    Reading what you wrote got me rethinking some other thoughts on this …
    I remember reading one study with the Tampa Scale of Kinesiophobia that showed it wasn’t particularly sensitive to change – I cannot remember the recovery outcome used. Maybe this is more chicken-egg …
    Also, are high fear-avoidance questionnaires scores closely associated with measured fear avoidance behaviours?
    Are fear avoidance behaviours (not questionnaire scores) situationally dependent, or more of a general behaviour pattern?
    Do we have any research considering whether people who score high on fear avoidance questionnaires, or score high on research lab-measured fear avoidant behaviour, also behave in a manner consistent to this when there are things that need to get done during their normal daily activities. (I would guess the research would need to occur in a non-insurance group who do not need to worry about getting cut-off benefits).
    … all back to that t-shirt idea again … and supportive of the idea that we don’t often get a chance to sit around and think about what we think about an idea.

  3. Hey Neil,
    Thanks for the post, I’d just add an observation that struck me when collecting fear avoidance data from patients following whipash injuries. I think it is potentially relevant to trying to untangle the causal relationships you mention.
    The issue is whether or not the sorts of beliefs that are asked about in the questionnaires (e.g TAMPA scale) are actually adaptive in the acute stage? If you have just had a car accident and have a really sore neck, is it not a good idea to avoid some of your more strenuous or intense phsical activities for a short period of time?
    If that is the case (maybe it isn’t I don’t pretend to know the theory inside out), then there is a question of timing as to when fear avoidance beliefs should become predictive/causative of something bad in the longer term.
    In this case getting at the chicken and egg question is even more difficult; measure too early and you will find no association (because everyone has (adaptive) fear avoidance at the beginning) and measure too late and you don’t know whether you are looking at a something causal, a response or an epiphenomena.

    Neil O'Connell Reply:

    Thanks Steve,

    Oooh, really good point. I’m going to need to chew that over. I wonder how long would we predict “too long” to be for those behaviours/ beliefs. Or maybe there is a “usual” level of FAB in acute injury and a “pathological” level.

    Geoff Reply:

    Hi Steve and Neil,
    This is a great post. I’ve encountered similar findings in my research looking at pain beliefs such as expectancy in WAD and Neuropathic pain. The literature suggests negative expectancy can contribute to variance in future outcomes. Expectancy theory suggests the same. In a study I am writing up, we indeed found this relationship. However, when we looked at interactions, we found that in patients with low and moderate levels of pain intensity, you indeed get what you expect, whereas those with higher levels of pain intensity catastrophizing scores are higher in patients with positive expectancy.
    To your point, I wonder about a similar relationship where acutely, patients with high pain adaptively avoid, and as you say, there comes a point in time when avoidance becomes maladaptive no matter one’s pain severity. In patients with moderate levels of pain acutely who hold avoidance beliefs, perhaps these are the folks that we might suggest have maladaptive beliefs about activity in the acute stage.
    I think there is something to the notion that fear-avoidance, in some circumstances can be adaptive.
    If you come across a large enough prospective cohort that enables interaction analysis, I’d love to help out!

  4. This problem of trying to go from a finding a relationship and finding causality is huge. It permeates decision making in medicine in general, and like you point out a prospective study trying to control for other variables is needed. I don’t know for sure, but I suspect the size of such a study likely makes it not feasable. Thanks for the article.

  5. Hello Neil,
    I am not certain how this idea fits in here, but it sure seems to me that we need to expand beyond FAM and include other things such as the FEM (fear-endurance model). There was a paper or two on endurance behaviour, in which they talked about how people with persistent pain do not always avoid things that will increase their pain. (I know I am at the end of the plank when I state) this is something we observe clinically too – though it seems less common in the “I need to prove that I am disabled” groups. Sometimes for some people, and often for others, the way we live our life when we are in pain is to grit our teeth, endure the pain, and get the job done. It is tempting to say that some people are fear-avoidant and others are not, but given human nature it might be more reasonable to suggest that fear-avoidance is situationally dependent. If you are wondering why I referred to as the FEM, this follows from an idea that these individuals are motivated by fear just as in the FAM, yet the fear here could be of something different – maybe losing one’s identity, of not feeling strong, of not being competent anymore, … . Regardless of the ‘which came first’ discussion, it remains enticing to stick everyone in the FAM. It is equally enticing to consider that for many people with persistent pain, when we help them perform activities that don’t lead to a flare-up AND lead to greater fearlessness, their brain’s can come to a sensible story that ‘it’s not so dangerous’. Less fear, less pain, improved ease of motion. And still no answer to the whether it matters which came first.

    Neil O'Connell Reply:

    Hi Neil,

    Interesting thoughts, that conjour up the perpetual truth established on this t-shirt: http://www.badscience.net/2008/12/i-think-youll-find-its-a-bit-more-complicated-than-that-and-other-excellent-christmas-gifts/ !

    I wonder how many of those FEM folk ever show up in the clinic. I suspect, if they are out there, then they would be systematically unrepresented in most chronic pain research as they would avoid the pathways to recruitment. Regardless if FAB is a key predictor then one might hope to see it regularly reflected in prospective studies. Maybe the fear is not the thing, or at least not on its own.

  6. Hi Neil,
    Great post. One frustration I have in the prognostic literature is when evaluating independent associations the result is often a modest amount of explained variance. Put another way, the determinants of persistent pain are wildly complex. The most robust predictor is pain intensity, but we know the factors that inform the expression of that number is also complex. It seems like many of these candidate predictors are fighting over such small scraps of variance. Moreover, as you’ve said, many predictor/outcome constructs seem to make good bedfellows.
    Are the models not quite right or the measures? Or is the process of acquiring chronic pain so complex it is actually a complex adaptive system that does not lend itself well to prediction?
    Keep up the great work BiMmers – I really enjoy the posts!

    Neil O'Connell Reply:

    Hi Geoff,

    Thanks! I agree the proportion of the variance in outcome most models offer is really small. So either we have the wrong variables, the right variables badly measured or the complexity simply trumps our efforts as you propose. Don’t know the answer (obviously) but the complexity picture looks pretty plausible. Tomorrow I’ll probably change my mind in a fit of optimism.

  7. Alan Eldridge says

    This study shows a relationship between disability and fear, but it does not show whether fear caused the disability or visa versa. When it comes to the treatment of persistent pain,I wonder if determining whether fear caused the disability or the disability caused the fear even matters? If you address the patients fear and catastrophising beliefs, would you be enabling the patient and decrease the severity of persistent pain?

    Certainly prospective studies on the subject matter would still be beneficial as addressing ones fears is (in my opinion) much easier to address in the acute stage than in the chronic stage of pain.

  8. Bård Bogen says

    Hi Neil, nice and informative piece. On a whim, I checked your published work in the above link, impressed that your work includes livestock (se entry #2).

    Neil O'Connell Reply:

    Hi Bard,

    I know, like to keep it eclectic!, ( truth, that’s definitely not me!)