I assume what you are talking about is what I have always called 'bucked shins'. This usually affects only 2 or sometimes 3 year olds. The usually get completely over it with age. How old is this horse now? Has he won or placed in any races? Is soundness a reason he is no longer running. Some are retired because of soundness and others because of slowness. Obviously, it is better to pick one up that retired slow and sound than fast and injured.
Can you ask the Vet that did this horse's Vet work at the track? When I used to buy OTTBs and OTQHs I always tried to get them from the owners / trainers and not dealers and always tried to talk to the Vet that did the trainer's leg work.
Are you going to have this horse Vetted before purchase -- as in a PPE? It is always preferable to speak to the horse's original Vet than to start all over with a Vet that does not know the horse (and a whole lot less expensive). There may already be x-rays out there for this horse and a complete Vet record.