Function


There are some very weird and crazy measures out there in pain assessment land… some of them take a little stretch of the imagination to work out how they were selected and what they’re meant to mean in the real world.

Functional measures are especially challenging – given that they are about what a person will do on a given day in a given setting, they are inherently prone to performance variation (test-retest reliability) and can’t really be held up as gold standards in terms of objectivity. Nevertheless, most pain management programmes are asked to provide measures of performance, and over the years I’ve seen quite a few different ones. For example, the ‘how long can you stand on one leg’ timed measure…the ‘sock test’ measure…the ‘pick up a crate from the floor and put it on a table’ measure…the ‘timed 50 m walk test’…the ‘step up test’… – and I could go on.

Some of these tests have normative data against age and gender, some even have standardised instructions (and some of these instructions are even followed!), and some even have predictive validity – but all measures beg the question – ‘why?’

I’m not being deliberately contentious here, not really… I think we as clinicians should always ask ‘why’ of ourselves and what we do, and reflect on what we do in light of new evidence over time. At the same time I know that each of us will come up with slightly different answers to the question ‘why’ depending on our professional background, experience, the purpose of the measure, and even our knowledge of scientific methodology. So, given that I’m in a thinking sort of mood, I thought I’d spend a moment or two noting down some of the thoughts I have about measures of function in a pain management setting.

  1. The first thing I’d note is that functional performance is at least in part, a measure of pain behaviour. That is, it’s about what a person is prepared to do, upon request, in a specific setting, at a certain time of day, for a certain purpose. And each person who is asked to carry out a functional task will bring a slightly different context to the functional performance task. For example, one person may want to demonstrate that their pain is ‘really bad’, another may want to ‘fake good’ because their job is on the line, another may be fearful of increased pain or harm and self-limit, while another may be keen to show ‘this new therapist just what it’s like for me with pain’. As a result, there will be variations in performance depending on the instructions given, the beliefs of the person about their pain – and about the way the assessment results will be used, and even on the gender, age and other characteristics of the therapist conducting the testing. And this is normal, and extremely difficult to control.
  2. The second is that the purpose of the functional performance testing must be clear to the therapist and the participant. Let’s look at the purpose of the test for the therapist – is it to act as a baseline before any intervention is undertaken? is it to be used diagnostically? (ie to help assess the performance style or approach to activity that the client has) is it to establish whether the participant meets certain performance criteria? (eg able to sustain manual handling safely in order to carry out a work task) is it to help the participant learn something about him or herself? (eg that this movement is safe, that this is the baseline and they are expected to improve over time etc).  And for the participant? Is this test to demonstrate that they are ‘faking’? (or do they think that’s what it’s about?) Is it to help them test out for themselves whether they are safe? Is it a baseline measure, something to improve on?  Is it something they’ve done before and know how to do, or is it something they’ve not done since before they hurt themselves? You see, I can go on!!
  3. Then the functional measures must be relevant to the purpose of the testing. It’s no use measuring ‘timed get up and go’, for example, if the purpose of the assessment is to determine whether this person with back pain can manage his or her job as a dock worker. Likewise, if it’s to help the person learn about his or her ability to approach a feared task, then it’s not helpful to have a standardised set of measures (unless this is a set that is taken pre-treatment and again at post-treatment). This means the selection of the measures should at least include consideration of predictive validity for the purpose of the test. For example, while a ‘timed get up and go’ may be predictive of falls risk in an elderly population, it may be an inappropriate measure in a young person who is being assessed for hand pain. It’s probably more useful to have a slightly inaccurate measure that measures something relevant than a highly accurate measure that measures something irrelevant. For example, we may know the normative data for (plucking something out of the air here…) ‘standing on one leg’, but unless this predicts something useful in the ‘real world’, then it may be a waste of time.
  4. Once we’ve determined a useful, hopefully predictive measure, then it’s critical that the assessment process is carried out in a standard way. That means the whole process, not just the task itself. What do I mean? Well, because there are multiple influences on performance, such as time of day, presence or absence of other people, and even the way the test is measured (eg If it’s timed with a stop-watch, when is the button pushed to start? When is it pushed to stop? Is this documented so everyone carries it out exactly the same way?) There is a phenomenon known as assessment drift (well, that’s what I call it!) where the person carrying out the assessment drifts from the original measurement criteria over time. This happens for all of us as we get more experienced, and as we forget the original instructions. Essentially we are a bit like a set of scales – we need to be calibrated just as much as any other piece of equipment. So the entire assessment needs to be documented right down to the words used, and the exact criteria used for each judgement.
  5. And finally, probably for me a plea from the heart – that the measures are recorded, analysed, repeated appropriately, and returned to the participant, along with the interpretation of the findings. This means the person being assessed gains from the process, not just the clinician, or the funder or requester of the assessment.

So over the Easter break (have a good one!), take a moment or two to think about the validity and reliability of the functional assessments you take. Know the confounds that may influence the individuals’ performance and try to take this into account when interpreting the findings. Consider why you are using these specific measures, and when you were last ‘calibrated’. Make a resolution: ask yourself ‘what will this measure mean in the real world?’ And if, as I suspect most of us know, your assessments don’t reflect the reality of carrying the groceries in from the boot of the car, or pushing a supermarket trolley around a busy supermarket, or squeezing the pegs above the head to hang out the washing – well, there might be a research project in it!!

2 comments

  1. Happy Easter to you too!

    The beauty of pain is that it does present in so many different ways, and it’s impact is equally as unpredictable. Hence measuring function is in theory a great idea, but in reality lacks a ‘gold standard’.

    I agree that timed up and go, for example, is pretty useless as an indicator for a young person with hand pain – but what about the subjective information that you gain? Avoidance, postural changes, guarding, loss of trunk rotation, changes in tone. All extremely useful pieces of information to help create a good clinical picture.

    Providers and most patients also want an objective measure to compare against, are they actually making any progress? Is the intervention making a difference somewhere?

    I think a time, number of repetitions, a weight provides a useful indicator of performance. No it doesn’t give a clear diagnosis, nor is it likely to tell you how the person is going to cope with a return to their previous job. But is you’ve identified that a person with chronic pain is ‘deactivated’, ‘deconditioned’ and perhaps fearful of certain movements or activities, then showing them how they are able to influence and improve something specific seems very useful.

    It also begs us to ask – where is the evidence? And this goes back to earlier rants, if we make everything specific to the individual, how can we gauge, overall, if our approach is beneficial, and if so just how much more beneficial is it than another intervention (or no intervention!). The positive about TUGT or 50m walks is that they are internationally recognised and comparable – we are talking a common language and can therefore compare outcomes, which must be better than working on gut instinct – and more reassuring for the less experienced clinicians without a wealth of knowledge to draw on.

    Love the article though – can’t get enough of the website, whether it winds me up, or calms me down!

  2. Glad you had some time to read the article – and comment – thanks! I hope your Easter has been going well too…
    I know that functional assessment is a vexed question: that’s precisely why I think more research needs to be made into developing robust measures, and most importantly, imparting to therapists/clinicians the knowledge of methodology to understand how to effectively manage the confounds that plague this type of testing.
    I think the first question, as I said above, is what is this assessment for? Why are we doing it? By answering this we’ll be able to identify an appropriate measure – or at least eliminate doing some that simply don’t work, or are measuring the wrong thing.
    What I don’t want to see is clinicians giving up assessment, being replaced by inappropriate, albeit accurate, assessments. A case in point? American Medical Association Guides to the Evaluation of Permanent Impairment, which are being used to determine disability. Impairment is not the same as disability. And the two can’t be measured the same way. So why are they being used to determine ‘lump sum’ payments for ACC where the payment is meant to be compensation for disability? Gggggrrr!

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