Dogs with hip dysplasia are most often limited in their extension of the hip joint. The normal hip should allow the femur to be parallel with the spine during full flexion and should allow 90 of external rotation, 45 of internal rotation, and ~180 of extension. The hip should be put through a limited range of motion and palpated for crepitus before assessing full range of motion. These points should form a triangle, with the point of the greater trochanter lying below the line connecting the ischium and iliac wing. To assess for coxofemoral luxation, the pelvic landmarks of the ischial tuberosity, iliac wing, and greater trochanter are palpated. Examination should begin with the foot of the limb in question, working proximally toward the hip joint. Palpation of the hip joint is usually best accomplished with the patient in lateral recumbency. To accomplish this, some animals may stand with their stifles and hocks more extended than normal, creating a somewhat 'straight-legged' appearance. When standing, affected dogs may appear to shift weight off of their hind limbs and onto their front limbs. All of these adaptations are an attempt to limit hip joint excursion, especially in extension. Patients may exhibit a variety of gait abnormalities, including unilateral lameness, bunny hopping, or pelvic/spinal swaying, and a shortened stride. Initially, it is important to confirm that the lameness is of orthopedic origin and not neurologic. Gait evaluation is useful for assessing changes in locomotion in patients compensating for hind limb discomfort or dysfunction. These two groups have distinctly different options for surgical management. For the veterinarian discussing treatment options, the important distinction to make is between young animals with joint laxity but no degenerative changes, and animals of any age with degenerative joint disease. Older dogs present with dysfunction that is more often due to progressive degenerative joint disease. Young dogs less than one year of age present with pain and lameness that is most likely due to joint laxity, subluxation, and synovitis. In particular, older dogs with progressive disease may be more likely to exhibit stiffness in the pelvic limbs, lameness that worsens with exercise, or muscle atrophy.Ī bimodal age distribution for affected animals has been described. Affected animals may present with a variety of clinical signs, including: a bunny hopping gait, difficulty rising, jumping or stair climbing, exercise intolerance, behavior change, or unilateral lameness. However, it is increasingly being diagnosed in small dogs and cats. Hip dysplasia most commonly affects large breed dogs. The individual variability is in the rate of progression and the degree of clinical signs exhibited by the patient. Virtually all animals progress from laxity to degenerative joint disease. It is these changes that are responsible for the chronic pain and lameness seen with progressive hip dysplasia. Inflammation, cartilage degradation, and joint remodeling are hallmarks of degenerative joint disease. It also causes the production of cytokines that contribute to cartilage degradation. Concurrently, inflammation results in an increase in joint fluid volume, contributing further to incongruity of the joint. Repeated subluxation causes cartilage fibrillation and destruction, remodeling of the femoral head and acetabulum, and periarticular new bone formation. Subluxation results in joint capsule stretching, which causes the initial pain and lameness associated with hip dysplasia in young animals. In turn, laxity leads simultaneously to subluxation, inflammation, and periarticular new bone formation. Polygenic and environmental factors contribute in a complex manner to cause laxity via morphologic changes such as joint incongruity or abnormal pelvic musculature, joint capsule, or round ligament. While various etiologies have been proposed, it is generally accepted that coxofemoral joint laxity is a principle component of hip dysplasia at an early stage. Simplistically, the pathophysiology of hip dysplasia can be described as joint laxity leading to degenerative joint disease. Screening for hip dysplasia in young dogs is important for treating affected individuals as well as for making breeding recommendations for owners. The etiology is multifactorial, having both genetic and environmental components. Large breed dogs are most commonly diagnosed, however small breed dogs and cats also are affected. First described in the 1930's, it continues to affect millions of dogs worldwide. Hip dysplasia is the most common developmental orthopedic disease in dogs.
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