Derby was born with malformed front legs. He can't walk normally on them. His owners found a solution from the company 3DSystems. The engineers there designed and printed out prosthetic legs for Derby to use.
The legs have rounded feet. This unusual design serves an important purpose. Peg-like prosthetic feet can get stuck into the ground easily. Derby's rounded legs, however, let him keep going over small obstacles.
Derby's owners report that he now runs at least 2-3 miles every day--and faster than they can! He certainly looks happy about his new legs, too.
-via Tech Crunch