In summary, this handsome fellow has had chronic navicular, with tightly contracted heels.
We have been battling a wry foot (bent sideways by imbalance) hoof conformation where the inside wall wears slower than the outside wall, and between trims this imbalance is accentuated as he walks on the outside wall and the inside wall wears slower.
The lines on the wall are highlighted growth rings and what I call "longest tubule" lines showing the longest wall.
I use these lines to visually illuminate wall imbalance, and suggest that they be used to help trim flare and imbalance.
We feel this imbalance started with thrush, as we found thrush deep in his frog corium on x-rays.
The discomfort of the thrush resulted in his weighting the outside wall to avoid frog pressure and "hoof mechanism", the natural expansion and contraction of the hoof as its weighted and un weighted.
The constant imbalance and pressure on the lateral (outside) wall caused the lateral edge of his coffin bone (P3) to degenerate. These Anterior views of one of his coffin bones with clearly degenerated bone can be seen on this update page: June 15, 2006 - X-Rays
At this point, we need to trim him so that he wasn't so out of balance at the end of his trim cycle. One of the regional vets, Dr Diane Isabel DVM, expressed the belief that the lateral edge of P3 would regenerate over time if we could keep the wall balanced throughout the trim cycle.
What we applied was a bevel that looked the same from a solar view, with equal amounts of wall height surrounding the sole, but thinned the wall on the longer medial sides so that they wore at a much faster rate than the lateral walls.
Before we noticed the Ps imbalance on the x-rays, the owner wanted me to try trimming the hoof from the sole to balance it mechanically.
As you can see from the sole shots below, lowering the wall on the long medial side of the hoof would invade the live sole on the medial side.
The reason that medial wall gets longer faster is because the horse wears the opposite side more. My concern was that lowering the medial wall into the live sole would make that side less comfortable and it would result in heavier dependency on the lateral wall.
We agreed to do it, once, to see if it would work. I was certain it wouldn't. The horse did wear his lateral wall more, and the difference was accentuated by the next trim.