Anatomy:

The hip is one of the body's largest joints. It is a ball-and-socket joint. The socket is formed by the acetabulum, which is part of the pelvis bone. The ball is the femoral head, which is the upper end of the femur (thighbone).

The bony surfaces of the ball and socket are covered with articular cartilage, a smooth cap that cushions the ends of the bones and enables them to glide easily.

A thin tissue called the synovial membrane surrounds the hip joint. In a healthy hip, this membrane makes a small amount of fluid that lubricates the cartilage and eliminates almost all friction during hip movement.

Bands of tissue called ligaments (the hip capsule) connect the ball to the socket and provide stability to the joint.

Common Causes

The most common cause of chronic hip pain and disability is arthritis. Osteoarthritis, rheumatoid arthritis, and traumatic arthritis are the most common forms of this disease.

Osteoarthritis: This is an age-related wear and tear type of arthritis. It usually occurs in people 50 years of age and older and often in individuals with a family history of arthritis. The cartilage cushioning the bones of the hip wears away. The bones then rub against each other, causing hip pain and stiffness.

Rheumatoid arthritis: This is an autoimmune disease in which the synovial membrane becomes inflamed and thickened. This chronic inflammation can damage the cartilage, leading to pain and stiffness. Rheumatoid arthritis is the most common type of a group of disorders termed inflammatory arthritis.

Posttraumatic arthritis: This can follow a serious hip injury or fracture. The cartilage may become damaged and lead to hip pain and stiffness over time.

Osteonecrosis: An injury to the hip, such as a dislocation or fracture, may limit the blood supply to the femoral head. This is called osteonecrosis (also sometimes referred to as avascular necrosis). The lack of blood may cause the surface of the bone to collapse, and arthritis will result. Some diseases can also cause osteonecrosis.

Childhood hip disease: Some infants and children have hip problems. Even though the problems are successfully treated during childhood, they may still cause arthritis later in life. This happens because the hip may not grow normally, and the joint surfaces are affected.

What is total hip replacement?

In a total hip replacement (also called total hip arthroplasty), the damaged bone and cartilage is removed and replaced with prosthetic components.

• The damaged femoral head is removed and replaced with a metal stem that is placed into the hollow central canal of the femur. The femoral stem may be either fixed with cement or "press fit" into the bone.
• A metal or ceramic ball is placed on the upper part of the stem. This ball replaces the damaged femoral head that was removed.
• The damaged cartilage surface of the socket (acetabulum) is removed and replaced with a metal socket. Screws or cement are sometimes used to hold the socket in place.
• A plastic, ceramic, or metal spacer is inserted between the new ball and the socket to allow for a smooth gliding surface.

When is surgery recommended?

There are several reasons why your doctor may recommend hip replacement surgery. People who benefit from hip replacement surgery often have:

• Hip pain that limits everyday activities, such as walking or bending
• Hip pain that continues while resting, either day or night
• Stiffness in a hip that limits the ability to move or lift the leg
• Inadequate pain relief from anti-inflammatory drugs, physical therapy, or walking supports

WHAT ARE DIFFERENT TYPES OF HIP REPLACEMENT IMPLANTS?

Metal-on-Polyethylene:

The ball is made of metal and the socket is made of plastic (polyethylene) or has a plastic lining.

Ceramic-on-Polyethylene:

The ball is made of ceramic and the socket is made of plastic (polyethylene) or has a plastic lining.

Ceramic-on-Ceramic:

The ball is made of ceramic and the socket has a ceramic lining.

Candidates for Surgery:

There are no absolute age or weight restrictions for total hip replacements. Recommendations for surgery are based on a patient's pain and disability, not age. Most patients who undergo total hip replacement are age 50 to 80, but orthopaedic surgeons evaluate patients individually. Total hip replacements have been performed successfully at all ages, from the young teenager with juvenile arthritis to the elderly patient with degenerative arthritis.

Risk

• Blood clots:
  Clots can form in your leg veins after surgery. This can be dangerous because a piece of a clot can break off and travel to your lung, heart or, rarely, your brain. Your doctor may prescribe blood-thinning medications to reduce this risk.
• Infection:
  Infections can occur at the site of your incision and in the deeper tissue near your new hip. Most infections are treated with antibiotics, but a major infection near your prosthesis might require surgery to remove and replace the prosthesis.
• Fracture:
  During surgery, healthy portions of your hip joint might fracture. Sometimes the fractures are small enough to heal on their own, but larger fractures might need to be stabilized with wires, screws, and possibly a metal plate or bone grafts.
• Dislocation:
  Certain positions can cause the ball of your new joint to come out of the socket, particularly in the first few months after surgery. If the hip dislocates, your doctor might fit you with a brace to keep the hip in the correct position. If your hip keeps dislocating, surgery is often required to stabilize it.
• Change in leg length:
  Your surgeon takes steps to avoid the problem, but occasionally a new hip makes one leg longer or shorter than the other. Sometimes this is caused by a contracture of muscles around the hip. In this case, progressively strengthening and stretching those muscles might help. You're not likely to notice, small differences in leg length after a few months.
• Loosening:
  Although this complication is rare with newer implants, your new joint might not become solidly fixed to your bone or might loosen over time, causing pain in your hip. Surgery might be needed to fix the problem.
• Nerve damage:
  Rarely, nerves in the area where the implant is placed can be injured. Nerve damage can cause numbness, weakness and pain.