Cause & Effect

I've thought a lot about the notion of cause and effect, and how it is such a difficult thing to get get a firm grip on. Indeed, from a systems point of view, our traditional ideas about cause and effect may be largely misleading.

When it comes to musculo-skeletal dysfunction and pain, the concept of X causing Y (where Y can be pain, tenderness, altered function and so on) is probably only 'correct' in trauma histories. You know, the patient who says "I was absolutely fine until I hammered my big toe..." etc.

For anything else ("it just seems to have built up for no reason over the last few weeks...") pinning down cause and effect is a lot harder. 

Actually, we always spend a bit of time asking the patient "What's changed or different then, compared to...?". And often the patient will finally confess to something (more work, taken up jogging, different car seat and so on) that allows us to say "Well, there you are then!". 

At this point the patient will often feel a bit better. There is a powerful human need to have some explanation for worrying things, and any answer - however thin and shaky - will often work for the patient. Indeed, there is some evidence that the patient's left hemisphere demands an explanation - as long as it kind of makes sense, whereas the right hemisphere is a lot happier with uncertainty (see McGilchrist). I digress, though suffice to say, woe betide the practitioner who fails to address the basic human need for a simple explanation. "Your facet joint has slipped..." may make a lot of us squirm - but it works.

So cause and effect is tricky. 

Actually, patients often seem to have some grasp of the concept of compensation. When we say that their mid back is hurting because the lumbar spine won't extend well, they often say "Ah, because it's compensating?".

As an aside, at this point I often explain to patients that a spine that is not working well does not just generate pain and stiffness, but uses more energy than a spine which is working as well as it can. In absolute terms, because the spinal system has to be a big consumer of  the total energy available to the human body, that has to be quite a lot. 

This always get me musing on what is the difference between adaptation and compensation and coping, or are they the same thing? 

The Oxford defines adaptation as "the process of change by which an organism or species becomes better suited to its environment".

And compensation as "something that counterbalances or makes up for an undesirable or unwelcome state of affairs".

Dictionary.com defines coping as "to face and deal with responsibilities, problems or difficulties, especially successfully, or in a calm and adequate manner".

Actually, all three words have other dictionary meanings as well, but the above seemed closest to what we have in mind and use in everyday practice life. 

So it seems that the word compensation may be closest to what we want.

Let's take an example. Say the left lumbo-sacral joint gets stiff in such a way that the segment can't bend to the left at all well. We can easily see that during locomotion, the spine will spend more time bending to the right than to the left - i.e. at that level of the lumbar spine, there will be a mass shift right, with a) an altered loading going through the right hip abductors during stance phase (compared to the left) and b) greater erector spinae output on the left side above the lesion (to counterbalance things). And so on.

If the compensation 'chosen' works optimally (meaning there is no better solution available) for this person at that moment in time, then all we can say is that there is the least increase in energy usage across the spine and the least probability of pain.

As professionals, we often use the term 'failure' or 'breakdown' of compensation - the idea being that if structures begin to hurt, as a secondary response to some original change in function, it is because the system has 'failed to cope'. 

I'm not sure this is always the correct way to think about things.

In one sense it is; for example, if a small car engine is badly tuned, it won't get up a steep hill, whereas a huge car engine, badly tuned, easily will. Similarly, if an athlete has enormous amounts of muscle and energy, he/she might easily 'cope' with a problem that would overwhelm someone a lot weaker.

But in another sense, it may not be. The fact that pain does not develop in the case of the athlete does not mean that the compensation chosen is optimal. Presumably, the best compensation would be one that produced the least increase in total energy usage in any time period, while minimising the risk of structures failing to cope at some point in the next or subsequent time periods. This has got to be a complex function of a number of factors - I wonder if it has been modelled properly?

One thing we can be sure about - human's will have similar ways in which they compensate for significant dysfunction, but will vary in the details. And successful compensation may fluctuate as it shifts the 'solution' around from period to period.

How about adaptation? Perhaps we ought to reserve this term for when the body has altered its structure, over time, as a response to the compensational functional changes that started the whole process? For example, a muscle forced to work 'harder' by altered function elsewhere might be able to adapt by become stronger. Presumably this can happen where the muscle is still able to work in the way it wants to (alternating power and relaxation cycles). This process of adaptation might not be possible if the muscle is instead asked to switch on in a more tonic way, something it was not designed to do. In this situation, there may be a more rapid path to coping failure and symptoms. 

We get clues from patient reactions to treatment as to whether we have helped 'causes' or 'effects'. For example, if a patient says "I felt great for a few days but then it all came back", then - clearly - all we did was successfully treat the compensation mechanism and allow it to cope a bit better for a while, but we have not treated further back in the chain. Whereas, if they say "I didn't feel any different for a few days, but then it started to get better", we know we have done something right.

Finally, when patients say "the sore bit was better following treatment, but the other - normally good - side was achy for a few days", we can probably surmise that structures that have been 'under-working' as a result of the original problem and subsequent compensation mechanism have had to do some real work, and groaned as they adapted to it.