How Does the Mineral Matrix React To Force

James Rooney DVM: "While much has been written about the treatment of fractures, very little attention seems to have been directed at the actual mechanism of fracture--how and why they occur."

Well, Doc, for horses little changed in 20 years since you wrote that. But several on-going "fracture resistance" studies for our species do help.

We're talking mineral here, rock, hard stuff, rigid, immovable material which on force application either holds together, maybe vibrates a bit, or blows apart. BUT, is there any "in between" here for our mineralized bone cells?

First we consider again in terms of materials the concept of "girding" or tightening against impending force. Muscle cells do this by expanding when squeezed, which in turn causes the little forks or phalanges sticking out from them and connecting to the neighboring cell to tighten. Tight, hard muscle cells break or tear much less easily than a slack cell at rest.

Can this same analysis be applied to an inorganic mineral matrix, i.e. on initial application of force does somehow this material sense the force and undergo any protective changes in response???

It seems so. "Fracture resistance" studies in terms of applied force refer to "load signals" or load signaling that causes reactions in the materials. These signals can cause either a "chemical" or a "mechanical" reaction withing the material which increases fracture resistance.

How does this work on the mineral matrix?
I am imagining that on application of pressure there is squeezing or compaction of the matrix which immediately resulting in backward resistance or pushing back against initial force. Mechanical inertia and energy then sustain this backward push and preserve the matrix, unless the force is "overbearing" causing breakage.

In addition to "backward resistance" (a term I just made up--unknown how a mechanical engineer might word this), I'm imagining the matrix can to a limited degree "bend" in several directions, which would further buffer and distribute and dilute the applied force.

In terms of how this applies to bone cells as few quotes located in my warm up post of August 15, 2007:

"...understanding the mechano-sensory bone system."

"Bone cells and/or cell network tend to adapt to external mechanical loads--they have a reaction to 'load signals'."

"Bone adaption depends on strain size, lasting time, frequency, history, type (pressure, tension) and strain distribution."

There is a vast body of evidence that the flow of fluids within the canaleculae and lacunae of bone is mostly responsible for the transduction of the mechano-chemical signal in bone cells."

This last statement is the clincher, and I'll have an illustration of a CANALeculae, next post.

Training:
Proving once again that you can find a needle in a haystack, last night as I was walking in the pasture on the 30 acres to "round them up" for training I walked right over my lost $400 cell phone with the 3.2 mega pixel camera lying there in the grass. What are the odds? The rain has destroyed it. Luckily I bought insurance.

Wed. night's work:
Rod: trotted a mile under tack. We're now 2/3 way around the pasture track with only the deer (lion in the bush) parts remaining. Hopefully we'll go all the way around tonight.
Art: 1.25 miles under tack--trot/gallop. Couple of sustained gallops but too dark to transverse the difficult parts. Sun dropping out of the sky like a rock this time of year.