If this twisted leg happened all of a sudden, your puppy likely has a fractured leg, If this happened over time, then it is not growing properly. You will need to make an appointment with a veterinarian for an orthopedic exam and radiographs, Depending on the findings your puppy may need surgery or at least wear a cast for a while to straighten out the leg and help your puppy grow properly. You also need to make sure that your puppy is getting proper puppy food for medium sizd dogs to ensure that he gets all the necessary nutrition to grow into a healthy dog, This leg will not come right by itself, so you will need the help of a veterinarian.