Most—but not all—inherited and developmental problems resulting in canine OA occur more commonly in larger dogs.
Hip and elbow dysplasia fit into this category because both have juvenile onset and are more commonly seen in large- (hip dysplasia) or large- and medium-breed (elbow dysplasia) dogs. Clinical signs of these conditions usually emerge in the first year of life; in the case of hip dysplasia, signs may emerge as early as 4 months of age.2,3 Elbow dysplasia occurs as a result of a mismatch in growth between the radius and ulna. Hip dysplasia, a hereditary as well as developmental disease, is the result of improper formation of the hip joints and subsequent progressive joint remodeling; this ultimately results in OA.
Osteochondritis dissecans is also a disease of young medium- to large-breed dogs between 6 to 9 months of age. Abnormal endochondral ossification impairs regional blood vessel development, and cartilage continues to grow, becoming thickened and less resistant to mechanical stress. Fissures in the abnormal cartilage may then develop, extending toward the articular surface and resulting in a flap of cartilage dissecting away from underlying subchondral attachments, which can lead to subsequent OA.
Cruciate ligament damage, whether due to chronic instability or an acute tear, is another common cause of OA. It is more commonly seen in large and giant breeds; adult dogs up to 4 years of age are also at higher risk for cranial cruciate ligament disease.4 Approximately 40% to 60% of dogs with cruciate injury in one stifle will develop cruciate injury in the second stifle at some point in the future,5,6 promoting further development of OA. Even with corrective surgery, radiographic signs of osteoarthritis continue to progress,7 and 30% of dogs may have long-term chronic pain.8
Additional disorders that may result in OA include hypertrophic osteodystrophy, which occurs in the long bones of young, growing dogs and osteochondrodysplasia, a group of developmental skeletal disorders that are typically genetic.
Unlike the aforementioned disorders, patellar and elbow luxation/subluxation—both important developmental conditions that can potentially lead to OA—occur more commonly in small breed dogs. Patellar luxation occurs bilaterally in approximately half of cases,9 with medial luxation occurring more frequently than lateral luxation.10