The most likely thing you’d find on an older horse is hock arthritis. The only question is - how bad does it look. Does it matter how good or bad it looks if the horse is serviceably sound? To me it doesn’t. The nice thing about those IM injections is they impact more of the body than most anyone is willing to xray. And, aside from injection site reactions (very uncommon), what’s the harm?
I’d guarantee there would be something seen in an older horse. The hocks may look terrible - does that matter for the serviceably sound horse? How far should someone xray looking for that One Thing that is most likely the cause of some minor unsoundness?
It doesn’t, and they aren’t. A client can absolutely say “Hey vet, I really want to have the hocks injected”. Plennnnnnty of owners do that, without any reason other then prevention, there’s no need for an actual diagnosis of arthritis, or sketchy joint fluid. I WOULD make sure there are xrays before doing it, because if you find out your sound horse has (nearly) fused hock joints, there’s no point in injecting, and you couldn’t anyway, there’s no joint space. But most of the time there will be space.
My vet has had no problem Rxing Adequan for me to use on my WB when he was 11-12-ish with an undiagnosed RH lameness. She said “you could start doing xrays of both hocks, and you might see some weirdness, but that doesn’t mean they are the problem. You could xray the stifles, and you might see weirdness, but that doesn’t mean that’s the problem, especially since you can’t flex hocks without stifles involved. You’d have to take him to NCSU to start looking higher up in his hip. OR, you can do a course of Adequan, which will impact more than just those parts, and if you see improvement, who cares what the cause was.” No diagnosis, and how does that equate to malpractice?
I’m ALL for judicious use of xrays to try to narrow down the source of an unsoundness. I’m all for flex tests, blocking, narrowing down where you want to start xraying, but none of that is required to want to do a course of Adequan/Pentosan, or a joint supplement with reasonable ingredients at reasonable amounts to see if they work after a few months.
Digging into xrays of a serviceably sound, older horse, is hunting for a reason to use a solution for a “problem” that might not even be a problem.