Panosteitis ("Pano") is common in young male dobermans. In simple terms, it is a form of growing pains. One day, he will be limping, holding up one paw...then a couple days later same thing, different paw. You might want to do some research on it online or talk to your vet. Assuming other diagnoses have been ruled out, pano is not serious or life threatening, and will pass in time. Tone down strenuous physical activity while he's limping. It's ok to walk around, but you don't want him to injure himself doing flat-out runs on a weak limb.