Stabilize the dog's leg as soon as possible using a board wrapped in a towel or another long, rigid object with protection against abrasive surfaces if you believe the leg is fractured. Then take the dog to the veterinarian for treatment as quickly as possible, according to M. Christine Zink of Dummies.com.
If the dog's leg has a compound fracture, a bone sticks out through the skin. Another clear sign of a fracture is a leg lying in an anomalous position. However, fracture is also possible even when the only visible symptom is swelling. If the dog lets you touch its leg in that situation, you may feel pieces grinding against one another, per Dummies.com.
If your veterinarian's office is right around the corner, put the dog on a level, firm surface in a vehicle, and transport the dog to the office. If the trip is likely to take a long time, splint the leg first. Wrapping a board around a towel and then using athletic tape or even electrical or duct tape to fasten the splint to the leg, both below and above the break, stabilizes the leg as much as possible. Even with the splint in place, getting the dog medical attention as quickly as possible is vital, as stated by Dummies.com.