I kept this very sweet quarter horse, Cash, in frog-support pads with two-part impression material to keep her sound. She has very tiny feet for her size, and they just couldn't support her in the long-run. It turns out that she has Cushing's disease, which causes a metabolic imbalance that was leading to constant laminitic episodes. At no particular time during her shoeing periods she would lay down and act like she was foundering, and two or three days later she was sound and could be ridden with no negative consequences to her feet or health. However, about 12 weeks after two of these episodes I noticed during my trimming for shoeing with pads and impression material that she'd have a crescent mood shaped bruise above her frog in just the spot that the distal phalanx (coffin bone or P3) would be. The twelve weeks coincided with about the same amount of time it would take for a laminitic episode grow out and to show up in her feet from the bottom as I trimmed out the old sole.
By the time that I trimmed out the dried blood spot, they'd be white underneath, showing that it's just a point in time in her feet, not a current problem. It's not a new bone bruise, but it does look like P3 had put some pressure on the solar corium--causing a bruising, a sign of laminitis.
I determined later that she was foundering during those reported episodes, but because she had on frog support pads and two-part impression material she had enough support to make it through the episode without really damaging her feet.
Cash was later tested for Cushing's disease, and came up positive. We could treat that with the current shoeing and meds, but she also developed a severe case of ringbone and had to be retired. She's living near Davis, CA now on a ranch for retired horses.
If you or your farrier ever see a crescent moot bruising over this area you can pretty much bet that the coffin bone has been pressing on the solar corium either by a founder or by sole pressure.