A Few Observations on the Marvelous Resilience of Bone and Resilience Engineering

I was fortunate to have the opportunity to attend redeploy this year. There were a lot of great talks and conversations and I took lots of notes. Thankfully, videos should be available at some point, you can click through to the link to get an email when they’re available.

This week I’ll focus on Dr. Cook’s keynote and will be collecting the rest of notes together soon.

Please understand that these are not intended to be an exhaustive account of every talk, though I do hope they give you a preview and an idea of where you may wish to start when they videos become available.

A Few Observations on the Marvelous Resilience of Bone and Resilience Engineering

Dr. Richard Cook opened the conference by teaching us an amazing archetype of resilience, bone. During his talk he said that he hoped in the future that if the audience were asked about resilience they would think of bone and at this point I certainly do.

As was consistent with his written work, the talk was informative and though it was about some complex mechanisms they were explained in ways that were approachable. Or is he summarized it “a simple talk about complex systems.”

Bone ends up being a good archetype of resilience because it is not static like we might perceive it to be. Our bones end up being completely replaced on about a 10 year time span, but we don’t really perceive this process because it is a dynamic balance between the destruction of old bone in the creation of new. It is a constantly active process that we don’t see it.

How and where the bone is remodeled is directed by mechanical strain.

It has properties that we can recognize from other complex systems in that it’s controlled by signaling:

• There is no controller
• It is a messy, layered network
• There’s lots of crosstalk

It being a messy, layered network is a hint, but Dr. Cook confirms for us that bone’s resilience is Woodsian. That is, of the type described by Dr. David Woods, in that it displays both graceful extensibility and sustained adaptability.

This system isn’t perfect though, it’s expensive, it consumes a lot of energy. It is also delicate and limited. Bone is a complex micro and macro architecture. This also reminds me of Woodsian resilience in that we can look at multiple “echelons” in the system or various zoom levels where we can different things.

New bone gets created along strain lines. This means regular strain leads to a regular pattern. It’s not that the perfect shape of say a femur is encoded in our DNA and the process just follows that blueprint, but regular strain helps create that. As a result there may be some sort of optimal strain experience (not too little and not too much).

The way bone is remodeled is:

• Continuous
• Locally directed
• Globally moderated

Because of the way bone gets healed, if there is a break mechanical stabilization becomes key so that these processes can remodel the bone in an ideal way. This is why some breaks require moving or pulling a certain way in traction to reduce the fracture.

Now we can begin to see that Orthopedists aren’t really healers in the sense that they are not doing the healing. They are creating conditions where the process (resilience) can be doing the best work. They are not creating resilience, they may not even need to understand the process itself.

In fact, there are documents from the Egyptians about 3500 years ago that describe reducing and setting fractures.

This ability to direct or engineer sources of resilience to contribute to better outcomes without a requirement to understand the source of it is one type of Resilience Engineering, perhaps the most common.

In the context of bone, there is another that is only a handful of years old. This second type relies on understanding the signaling that takes place in order to direct this process, especially that of the role of Parathyroid hormone-related protein (PTHrP). There has been some research around using microgram amounts of the signaling chemicals to fight diseases such as osteoporosis. This isn’t easy though as various animal models have shown that there is a risk of tumors or other bone abnormalities when taking this approach. If you’re curious here are some records of an early phase 2 clinical trial of a similar approach to what Dr. Cook describes.

This reveals to us some contrasts of this other type of resilience engineering. In this case it:

• Alters resilience
• Requires a deep understanding of the source of resilience
• And it also generates new types of hazards.

We could say that the first type is engineering that exploits resilience, whereas the latter type is engineering the resilience itself.

Takeaways

• Bone is an excellent archetype of resilience that can be used to understand more about resilience engineering
• Forms of resilience engineering in bone have been going on for about 3,500 years
• Bone reveals to us that there are two different types of resilience engineering.
  • We can utilize and direct sources of resilience without understanding the underlying mechanism or the source itself,
  • or we can alter the source of the resilience itself. However, doing so requires a deep knowledge of the underlying processes and can introduce new types of hazards.