"Osteochondrosis occurs commonly in the shoulders of immature, large, and giant-breed dogs. The lesion usually appears on the caudal (back) surface of the humeral head. Osteochondrosis begins with a failure of immature cartilage to form bone in the humeral head. This failure leads to abnormal cartilage thickening. Increased cartilage thickness may result in malnourished cartilage cells that die. Loss of these cartilage cells deep in the cartilage layers leads to formation of a defect at the junction between cartilage and bone. Subsequently, normal daily activity may cause fissures in the cartilage that eventually communicate with the joint, forming a cartilage flap. It is with the formation of a flap that osteochondrosis becomes [OCD]. OCD is the form of osteochondrosis that is associated with pain and dysfunction. In some cases, the resulting flap occupies as much as half the humeral head. The cartilage flap may completely detach from the underlying bone and become lodged in the back of the joint pouch. Free cartilage flaps can lodge in joints and may increase in size with calcification becoming 'joint mice' which can be seen on radiographs.

The causes of OCD are multifactorial with genetic and nutritional interactions thought to be the central factors. Risk factors for OCD may include:

Breed genetics (Polygenic trait, Age, Gender, Anatomic abnormalities, Rapid growth, Nutrient excesses (primarily protein, energy, calcium, and phosphorus), Trauma Due to the high frequency of occurrence within certain breeds of dogs and within certain bloodlines, heredity may be an important factor. Males are more commonly affected than females" (American College of Veterinary Surgeons, 2023a)