dog w/ hurt leg

Question
I have a 5 mo old Yorkie pup. I'm not sure what happened to him but for 2 days he's kept his back left leg lifted up. He won't put it down at all. But he doesn't seem to be in any pain. He still runs around(w/ 3 legs). He doesn't yelp or jump when I try to move or press on the leg to see where it maybe sore. There is no swelling or obvious problems beside him not using it.  When he keeps it up it just kinda is there almost limp like.

Answer
Your puppy could have done many things to hurt his leg.  I would be most concerned about fractures or a soft tissue injury (such as a muscle, tendon, or ligament strain).  Young puppies are very playful and he probably injured himself jumping or playing.  If he isn't bearing any weight on the injured leg after 3 days, he should have an x-ray of the leg.  The x-ray will determine if there are any broken or dislocated bones.  If he is still painful, your veterinarian can prescribe pain medication to make him more comfortable.