It could be a variety of things from the hoof all the way up to the shoulder and impossible to tell from a description. The fact that the leg is non weight bearing is concerning, I am reticent to give advice over the net. Best to get a vet out for this one.
It could be an abcess, do you have acess to hoof testers? It is not common for TB's to go lame necessarily although they are not always the sturdiest of breeds in general, thanks to poor breeding in the racing industry and often a tough start to life at the track.
Hope you sort things out!
All horses deserve, at least once in their lives, to be loved by a little girl.
Last edited by sarahver; 02-09-2011 at 06:04 PM.