Hip dysplasia (HD) is a developmental disorder of the hip joint. Over time, if the hip ball and socket joint are not perfectly matched in shape and size, they can wear against each other. The abrasion finds softer or stressed spots and creates pits of uneven erosion, which develop into painful osteoarthritis (OA) in the joint. Similar joint mechanics and injury can occur at the elbow or hock, but hip dysplasia is the most common orthopedic trait in all dogs.
Hip laxity is a term for identified genetic predisposition to HD and OA. It is a condition of the soft tissues in the joint, identified by observation of uneven space between the ball at the head of the femur and the socket edge, called the acetabular rim. Hip laxity is a latent condition which has not yet created any observed symptoms or x-ray evidence of disease.
Hip health is assessed through observation of the dog at play and work, manual manipulation of the joints and radiograph visualizations, x-rays. Not all dogs with visible x-ray damage appear to have pain and not all with pain have hip abnormalities on x-ray. Other soft tissue injuries can cause similar hind limb weakness or lameness. (Lane, n.d.)
Canine hip dysplasia is understood to be inherited through a number of unidentified genes. It is also significantly influenced by environmental factors. Identified first in 1935, it is commonly known as the leading cause of debilitating hip osteoarthritis and crippling in herding dogs, especially large and giant breeds. The condition is suspected in dogs with lameness but is only officially confirmed through x-rays showing pitting of the ball or socket.
How does HD occur?
Puppies are born with perfect hips. (Oberbauer A. K., 2017) (Institute of Canine Biology, n.d.) In fact, puppies don’t actually have formed hip bones. (Dog Solutions, n.d.) X-rays show the difference between formed bone and cartilage at the end of the femur at one day of age. Cartilage is soft material that will ossify over time to become bone, hard material which is visible on X-ray.
At birth, the femur and acetabular rim fit perfectly and are connected by a strong ligament. Some pups may have congenitally weak ligaments, much more prone to joint injury. As the puppy grows, over exercise, over feeding and genetics can all cause the ligament to stretch or break, and the joint to become loose, held only by muscles. The joint surfaces soon become less well matched, creating uneven joint space, wear at sharp points and the beginning of osteoarthritis. (Institute of Canine Biology, n.d.)
While many factors influence the incidence of HD, a restricted diet and managed body weight can significantly affect the timing and severity of symptoms. HD develops as the pups mature depending on both genetics and environment. HD is characterized by instability and subluxation of the hip joints which causes erosion of the joint cartilage and joint lining. Elbow dysplasia (ED) results in osteoarthritic changes which change the shapes inside the joint and cause lameness. Both HD and ED are influenced by genetic and environmental factors. (Pfahler, 2012)