Originally Posted by loosie
Not sure I can remember the entire details of exactly how(sorry!), but the distal sesamoid is sitting further under P2 when there's a broken back axis and weight through the leg pushes on it. Having a play with a 'knackered' leg that has been cut sagitally, it's pretty clear.... much better than my explanation I'm sure!
I would consider this more as a state of compression. Upward compression from solar forces, and downward compression from p2. W/ a broken back axis it is further compressed by the DDFT due to elongation of the lever (reduced flexion of the DIP and PIP joints). Though I don't have enough physics background to define the difference between compression and load bearing, and am sure the two can be used together at times.
Of course you don't have to have a broken back axis w/ a short pastern. These same concerns can be stated of a horse w/ long pasterns and a broken back axis. All the more reason to trim and/or shoe around the COA(center of articulation).