Hi Alex,

this is something that occurs in our large breed puppies often.   PetMD has an article about it copied below.  I find it interesting that the suspected cause if over reaction to vaccination.  Just for the record we do not over vaccinate dogs.  They only get the minimum required by state law and not the feel good shots peddled by most vets. 

What to do:

1. reduce vaccination

2. reduce physical activity to moderate level

3. cut down on high protein food

4. switch to raw food diet

5. supplement your food with Glucosamine and Chondroitin (Nupro has a great supplement)

Please see below.

Hypertrophic Osteodystrophy in Puppies

Hypertrophic osteodystrophy is a disease of the front limbs in large-breed puppies. Affected puppies suffer from a noninfectious inflammation of the bony spicules (pointed, mineral structures) in the metaphysis of the long bones. The metaphysis is the conical part of the bone between the epiphysis (the growing end of the bone), and the diaphyses (the shaft of the long bone). The most severely affected bones are those that grow most rapidly. Swelling around the metaphyses, and bone deposition, cause widening of the metaphyses. Tiny fractures of the bony spicules in the metaphyses, and metaphyseal separation occur close to and parallel to the physis. The physis is the epiphysial cartilage in the joints – the soft, connective part of the bone that hardens (ossifies) after full growth has been reached, joining the parts of the bone into one. There may also be ossifying periostitis, a painful inflammation of the most external layer of the bone, the periosteum. Ossifying periostitis can cause bits of the periosteum to break off and mineralize in the soft tissues of the leg, and soft tissue in other organs may mineralize as well.

Affected puppies may also have accompanying signs of pneumonia and diarrhea. While the cause of this disease is unknown, it is currently suspected to be a hyper-reactive response to vaccination.

Symptoms and Types

• Symmetrical lameness (mild or severe), most often in the forelimbs
• Depression and reluctance to move
• Warm, swollen metaphyses (the soft, or growing part of the long bones in puppies)
• Fever, as high as 106° F
• Lack of appetite
• Weight loss
• Dehydration
• Diarrhea
• Possible pneumonia

Causes

Suspected (but not proven) to be a reaction in the bone-producing centers to vaccination.

Diagnosis

Your veterinarian will perform a thorough physical exam of your pet. While a chemical blood profile, a complete blood count, and a urinalysis are good indicators of possible systemic disease, radiograph imaging of the legs is crucial for diagnosis of hypertrophic osteodystrophy. Thoracic (chest) radiographs will also be taken if pneumonia is suspected.

http://www.petmd.com/dog/conditions/musculoskeletal/c_dg_osteodystrophy

Best wishes for you and your pup.