Broken/fractured finger

My middle finger on my left hand hurts when I bend it.  In a resting position I am experiencing a throbbing pain. Most of the pain is around the first upper most joint.  This injuer occurred when my dog pulled and the leash somehow became entangled around my fingers. How do I know whether it is broken?  

[Dr Arora]

Suspect fracture when you have pain and swelling with decreased range of active motion, and possibly deformity, are reported after a history of trauma, tenderness to palpation; pain with passive motion, swelling and ecchymosis may be present, Radiographic exam is diagnostic; comparison views may be helpful.