I know way more about the structures of a horse's lower legs and hooves than I wish I did - no, that's not really true, it's good that I've had to learn these things although the circumstances have been less than ideal. I've had one horse (Promise) who suffered a catastrophic fracture of the large (P1) pastern bone, resulting in our losing her at age 10. Then Maisie's continuing problems with her hind suspensory ligaments and ultimately the left hind deep digital flexor tendon led to my decision to retire her at what is probably age 14 or so. Now Dawn's having some issues and the vet made a visit today to help us figure out what's up with her.
I almost felt a bit silly - Dawn is really much improved. She's walking completely normally, with her slap-the-hoof down determined walk - if you look closely you can see that she's landing heel first. The heat in her right front foot is gone. When the vet looked at her, her lower legs were clean and tight - pretty good for a TB who is 13 and who raced and who also has done some jumping. She had no sensitivity to hoof testers. On trot-out, she also looked good. Then the vet did some flexion tests, and it pretty quickly became clear that the lower leg on the right front is the issue - the flexion of the foot and pastern joint resulted in her looking fairly lame at the trot.
The vet recommended that we do nerve blocks to isolate the problem a bit further. Look at this diagram of the internal structure of the hoof and lower leg, which will help you follow what I'm saying. With nerve blocks, the vet usually starts at the bottom and works up until the blocks produce a noticeable improvement in the trot-out after flexion. So she injected above the joint between the large and small pastern bone - so just above the hoof - and voila! 70%+ improvement on trot-out. So that means the problem, whether with a joint or soft tissue, is very likely below that level - so the coffin joint (between P3 and P2, or coffin and small pastern, bones), joint between small pastern bone and large pastern bone (P2/P1 joint) or the joint surfaces around the navicular bone, or the various soft tissue structures supporting the hoof and lower leg bones inside the hoof capsule.
The vet didn't have her x-ray machine with her and will come back on Tuesday to take some right front x-rays to see what if anything we see. I'm pleased that Dawn has improved so much, but a little worried that she still flexes lame showing a problem that's still there. At least I was right about it being the right front - some small consolation, I guess. I'm cleared to ride her at the walk between now and then, so that's good!
(Oh, on a horse search note - I now understand a possible reason why horse #2 hasn't sold - the trainer who's marketing her seems pretty uninterested in getting her sold - I've talked with him and he promised photos, and I've e-mailed him twice, and nothing. Perhaps he's getting some nice board checks and training fees to keep the horse around, who knows?)