Limping for no reason?

My 8 month old mini yorkie limps but no one has every stepped on him he has never got hurt. He jumps of the furniture and stuff but he lands just fine and on carpet. He only limps every now and then but I don't know why he limps. I've checked his legs and he doesn't yelp or anything when i move his leg so i didn't think it hurt. Please help

[Aleda M Cheng, D.V.M., C.V.A]

Yorkshire's can have a number of congenital joint diseases such as luxating patella, avascular necrosis of the femoral head and many others, and 8 months of age is not too young to acquire Lyme or other tick borne disease.  All of these are best evaluated by your vet.