I'd certainly have the vet look asap. However if there is no lameness I would doubt there was a fracture. Have you trotted him up on a hard, level surface? If he's sound trotting up, lunge him on a hard surface on a small circle, known as 'the circle of death' to some haha, it puts a lot of pressure on the joints and will, in the majority of cases, show up any lameness. If he's not lame trotting on a small circle on hard ground, I would put my money on it that there is no fracture present.
Looks more to me like a haematoma IMO. Often if they get a knock/bite/kick or some kind of impact, even if he knocked against a fence or tree, or rolled on a rock, they can develop into a haematoma. A haemotoma is just a collection of blood which shows the same symptoms as a fracture, and is basically one of the ways the body can slow internal bleeding. Much like a bruise but it comes up as a lump so can be sensitive to the touch. They don't cause any problems and usually dissolve back into the body after some time, although some may continue to grow and will need to be drained. Either way, not a real big deal ;)
I'd get the vet to check it out anyway, just in case.
Last edited by Kayty; 05-11-2010 at 06:06 AM.
Reason: Typo ;)