Hip Replacement Health Article

Joint function

Restoration of joint function is the other major purpose of hip replacement surgery. The hip joint is one of the most active joints in the human body, designed for many different types of movement. It consists of the head (top) of the femur (thighbone), which is shaped like a ball; and a part of the pelvic bone called the acetabulum, which looks like a hollow or socket. In a healthy hip joint, a layer of cartilage lies between the head of the femur and the acetabulum. The cartilage keeps the bony surfaces from grinding against each other, and allows the head of the femur to rotate or swivel in different directions inside the socket formed by the acetabulum. It is this range of motion, as well as the hip's ability to support the weight of the upper body, that is gradually lost when the hip joint deteriorates. The prostheses that are used in hip replacement surgery are intended to restore as much of the functioning of to the hip joint as possible. The level of function in the hip after the surgery depends in part on the reason for the damage to the joint.

Disorders and conditions that may lead to the need for hip replacement surgery include:

• Osteoarthritis (OA). Osteoarthritis is a disorder in which the cartilage in the joints of the body gradually breaks down, allowing the surfaces of the bones to rub directly and wear against each other. Eventually the patient experiences swelling, pain, inflammation, and increasing loss of mobility. OA most often affects appears most often in adults over age 45, and is thought to result from a combination of wear and tear on the joint, lifestyle, and genetic factors. As of 2003, OA is the most common cause of joint damage requiring hip replacement.
• Rheumatoid arthritis (RA). Rheumatoid arthritis is a disease that begins earlier in life than OA and affects the whole body. Women are three times as likely as men to develop RA. Its symptoms are caused by the immune system's attacks on the body's own cells and tissues. Patients with RA often suffer intense pain even when they are not putting weight on the affected joints. One man described his pain as " … like a hot poker that's stuck from this hip right through to the other one."
• Trauma. Damage to the hip joint from a fall, automobile accident, or workplace or athletic injury may trigger the process of cartilage breakdown in the hip joint.
• Avascular necrosis. Avascular necrosis, which is also called osteonecrosis, is a disorder caused by the loss of
  blood supply to bone tissue. Bone starved for blood supply becomes weak and eventually collapses. The most common reasons for loss of blood supply include trauma, the use of steroid medications, certain blood disorders, and alcoholism. Avascular necrosis often affects the top of the femur that forms part of the hip joint. It develops most frequently in adults between the ages of 30 and 50.
• Ankylosing spondylitis (AS). Ankylosing spondylitis is a less common form of arthritis that primarily affects the bones in the spine and pelvis. These bones gradually fuse together when the body replaces inflamed tendons or ligaments with new bone instead of elastic connective tissue. AS typically develops in the patient's late teens or early twenties, with three times as many men affected as women.