Understanding Hip Dysplasia
The hip joint forms the attachment of the hind leg to the body and is a ball and socket joint that allows the leg to move through a wide range of motion. The ball portion is the “head of the femur” (= thigh bone) and the socket is termed the “acetabulum.” Hip dysplasia (HD) is a developmental (or growth) disorder that begins with hip laxity and progresses to arthritis over a period of months to years. The term HD simply means that the hip joint does not form normally, and the ball and socket do not fit together properly.
Even though most puppies are born with normal hips, genetic and other factors (such as body type, growth rate, exercise, nutrition) are the reason for ‘loose’ hips, which is the cause of instability within the hip joint called subluxation. Subluxation occurs when the head of the femur partially rides up on the outside edge of the acetabulum. This process causes joint inflammation, swelling and pain and wears down the cartilage within the joint, causing exposure of the underlying bone. Cartilage is the coating of any joint that ensures that motion is frictionless, smooth and pain-free. Without cartilage covering the joint, the joint surface becomes rough and uneven resulting in motion becoming painful.
Over time, arthritis develops, limiting the range of motion in the hip joint, and further causing pain and discomfort. Because of these two “phases” of HD the disease is termed “biphasic.” Young animals frequently present because of the pain associated with hip laxity and joint inflammation; older animals present because of the secondary arthritic changes. Whether your pet shows signs at a young age or at a later time depends on the severity of the disease.
Clinical Signs of Hip Dysplasia
The most common indication that a dog may have hip dysplasia is bilateral (both sides) hind leg lameness, stiffness or decreased activity level in any large breed dog. Many dogs show difficulty rising, not wanting to jump into the car, tiring easily, decreased willingness to play, ‘bunny hopping’ or waddling gait and short strides in the rear legs. The onset of clinical signs may appear suddenly but, in general, is a slow progression. Exercise typically makes the lameness worse. Although the disease is almost always present in both hip joints, one side is usually more severely affected based upon clinical signs and palpation. Since both rear legs hurt, dogs do not limp constantly, which may make the problem less obvious.
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