Is the problem posed by trying to understand the way the spine works complex or complicated – or both?

Does it matter, you might ask? Well, let’s see if we can shed some light on the difference between the two.

A complicated problem is one where there are lots of parameters. For example, if we have two members of a set (a, b) there can only be one relationship between the two. For three members, it is three. For 4, it is 6. We can see that as this set gets larger, there is a step change in the number of interactions between the members (a triangular number sequence). With a complicated problem, the interactions between all members of the set are fixed and unvarying. Chess is like that.

So far so good. Because all that means is that a complicated problem is one where it becomes more difficult to ‘see’ what is going on as the number of parameters rises. But, there are – in principle – no computational impediments to understanding the system if we have sufficient time and a powerful enough number cruncher. That’s why chess programs can now beat top human players.

What is a complex system? To understand this, look at weather forecasting. People used to think that forecasting the weather was an example of a complicated problem. “If only we could measure all the starting parameters of a weather state, we could forecast the weather etc.”. But, experience since the mid 60’s and the work of people like Lorenz has shown how calculating changes in the weather state is difficult. This seems to be for two reasons.

First, there are non-linear relationships between many of the different weather ‘factors’; this makes it even more difficult to predict a change in the state of the system for any given number of, relationship between, and change in variables.

Secondly, the state of the system at any point becomes extraordinarily sensitive to the starting position of the variables (the so-called ‘measurement problem’, where small changes in starting conditions have dramatic effects on the predicted system state).

So we find weather forecasts are fairly reliable up to 4-5 days, but then tail off dramatically, despite impressive models and incredibly fast super-computers compared to 20 years ago. Weather is complicated, but its predictive difficulty is because it is a complex system.

And the spine? Well, there are a huge number of variables that affect spinal function and healing responses (two of the things we are most interested in). That just makes it really *complicated*. What makes it *complex* is that the physiology of function and structure is all about non-linearity (for example, the way that collagen can suddenly fatigue, or how homeostatic negative feedback loops can fail). Further, we know it is impossible to measure accurately any of the variables in the system.

So the spine is at least as complex as it is complicated. Why does it matter if the spine is an example of a complex or a complicated problem?

Well, the reason is that despite the challenge posed by complexity, it is possible to see beyond the complexity and to simplify in a way that adds value.

See the TED talk below for a neat explanation of this.

What Eric Berlow argues is that you can look at *complex* systems to extract meaning and make predictions, but you can’t do this with a very *complicated* system.

If the spine was just complicated, our attempts to simplify and predict by looking for patterns and heuristics would be futile.

But because the spine undoubtedly has complexity, they probably aren’t.