What would you write if this were a question on your 2018 final year Podiatry exam? What do you think? Is it dead? Say it out loud now before reading the rest of this blog.. go on….Ah! there you go (thought so!).
I have changed my thoughts on foot biomechanics so much that I now believe foot biomechanics is in fact “dead”, or at least it underspecifies the topic to such a degree that we are doing the foot (and therefore our patients, profession and each other) a disservice. Here is my argument against “foot biomechanics”.
The foot is not a compilation of interconnected mechanical components that respond precisely to the laws of mechanics. It is a complex matrix of at least 11 biological tissues (i.e. skin, fat, muscle, tendon, joint capsule, ligament, bone, cartilage, fascia, nerves, blood vessels….) that responds to external loads through the symbiotic relationship between the motor control system and tissue properties. The overall system is also able to learn and adapt over time. The behaviour of the foot is under active control of a system that measures the status of the foot, communicates it, makes sense of it by integrating foot status with other information, and responds to it with new decisions about muscle forces and thereafter influences movement. Critically, at no time is the foot ever a purely mechanical structure, other laws are always at play.
The foot is only ever a pure mechanical structure when it is detached from the control system. Have you ever held a fresh cadaver foot? It’s quite difficult to make the foot stand normally or simulate ground contact in a way you would recognise as “gait”. It just flops about and is quite unwieldy. It is not what you see in clinic or when you take your shoes and socks off.
The foot is therefore never a purely mechanical structure and it is always under some level of intelligent control. It follows that we should think of the foot as an organ with wholly integrated sensory and mechanical system components. Also, we must assume these two co-exist whenever we discuss foot function, foot types, orthotic therapy and so on.
Having absorbed that, now reflect on the foot biomechanics “talks” we hear at conferences (including mine!), or recent podcasts you heard or papers you read. How does the sensory function of the foot feature in the common podiatry narrative about foot function? It rarely does. This is why I think we have underspecified foot biomechanics and at the UK podiatry congress in November I proposed that we lose “foot biomechanics” and move to the term “foot neurobiomechanics”.
There is another reason for this change. Over the last 2 decades our understanding of foot structure and function has greatly improved thanks to biomechanics research by teams across the world. Much of this, through necessity, has assumed the foot is a pure mechanical structure. It has been a steep learning curve (and fun) and the more research we did the more we learnt. However, I “sense” the angle of our learning curve starting to taper off. Or, at least, let’s ask what will fuel the next 20 years of learning about foot function?
I believe the integration of our current foot biomechanics knowledge with insights from motor control, neurophysiology and related domains (e.g. tissue biology) will drive advances in foot function more than pursuing a pure mechanics paradigm. This broader perspective will provide a more valid explanation of now multi system disease (e.g. diabetes) affects foot function and health (not just the how it affects it, but WHY), and explain how (not just whether) interventions work (or not). It should also open the door to the responsible introduction of new interventions or adoption of those from other disciplines e.g. movement retraining, foot exercise and sensory stimulation.
My point is this. “Foot biomechanics” is itself a simplification of a complex system and therefore a model through which we have represented the foot. As a model, there are some assumptions we made and we occasionally need to go back and check the model is still appropriate. It think the mechanics model has served podiatry and foot health really very well thus far, but needs a reboot with a contemporary twist.
How many marks would you give me? And what next?
Podiatry exam 2028: Question 3. “Foot neurobiomechanics is dead. Discuss.”