Out of curiosity who do you call when your horse has a 'back problem'? For example the vet, physio, mctimoney manipulators, osteopath etc and what makes you choose them?
If I think a horse has a "back problem" or is tight in the back I would call the Vets as IME many back probs are secondary to something else, which may need resolving.
If the Vet thinks Physio is necessary or a good idea then I will get the Physio out- I've used the same equine physio for years, only use them if there is a specific problem, I trust my physio's judgement and she is regarded very highly too.
a true back problem then vet. if just bit tight/sore maybe started bucking or odd behaviour with no really obvious cause of pain the physio but would normaly consult vet first