The most common cause is callus formation. Calluses frequently occur in large, shorthaired breeds of dogs that sleep on hard surfaces, such as wood or concrete.
To manage this condition, the sleeping areas of the dog should be changed. Soft bedding, such as foam rubber padding should be used.
Calluses can become infected, and conditions other than calluses can cause the skin changes you see on your dog. Therefore, it would be a good idea to have your veterinarian check any skin changes on your dog's elbows.