Microfracture: How Big A Threat?

There's enough information available that what follows is hypothesis instead of wild conjecture.

The illustration at left depicts a theoretical mineral lattice of a single bone cell at the atomic level. During the course of the breeze this structure will undergo tremendous pressure on a repeated basis albeit max force applies only for an instance. If you doubt the degree of force take a run down your sidewalk at 10 mph, concentrate on the force in your tibia which you'll by feel realize is quite significant with every stride, and multiply that by about 10 to understand what's happening in a similar sized cannon bone in your horse.

It's reasonable to suppose that in any one breeze/race of 240 strides or hits that a particular branch of the above matrix might fracture, that there might be a sequence of breaks, or the whole thing might be crushed. The concern this provides us, though, must be placed in context.

1. We are talking about a bone cell in mid cannon midway through the bone. Cells at the condylar aspect or in a state of new development at the bone surface require different analysis.
2. We have "conditioned" bone--i.e. we've gradually and carefully brought our horse and its bone structure up to this point.
3. "conditioned bone" postulates a matrix and collagen tightly packed with bone glue proteins and also with cells strongly buttressed against each other. That a single matrix branch or even an entire cell might be crushed here or there is less significant in this environment.
4. Absent unusual force (compared to normal forces) any fracturing is likely to be diffuse (see last post) instead of concentrated in a single area--i.e. post breeze we have fractured branches or cells spread randomly throughout the bone instead of in a pattern in a particular area.

Thus, I'm supposing post breeze that throughout the cannon bone there may be fractured matrix branches or crushed cells, but that these are scattered and diffuse.

What percentage of total bone cells might be totally or partially fractured? I'd doubt a lot in conditioned bone. Absent unusual force during the breeze, I'm thinking maybe 1% of total bone cells suffer damage. How do I justify this 1% figure. The best circumstantial evidence that the damage is at 1% or less is that our conditioned horses by and large avoid fractures. In conditioned horses the structure holds up indicating the damage is probably restricted to 1% of cells or less.

How significant is 1% destruction per breeze? We know that at any one moment in the every day life of bone that 4% of all bone cells are under construction, either being torn down or rebuilt by the osteo blasts and clasts. Adding another 1% seems fairly insignificant in this context.

There are concerns though, even with the 1%. How long does it take to repair the fractures? If we do 10 breezes a month do we then have 10-15% of the bone in jeopardy etc. Continue next post.

Training:
Sat. 8/30: Art 1.75 miles tack includes 1 mile gallop. Rod: 1 mile tack, trot-walk, and 2 miles slow gallop riderless.
Sun. 8/31 Art: tack: 4 x 2f gallop. Rod: tack 1 mile trot.
Mon. 9/1: Art: tack 4x 2f gallop. Rod: tack 1 mile trot. Both horses then did riderless speed work in near dark conditions. It was pretty ragged as the (damned) 2 year old kept hiding and we were unable to find him in the dark. But, got in some speed stuff. Art refused all lead changes today, and Rod is back to throwing his head. Progress I'm supposing, but in the wrong direction.