Replacement of the hip joint has become a common operation due to the advances in surgery and the quality of artificial joints. About 15,000 hip replacements procedures are performed in Australian and New Zealand every year.

The hip joint is a ball and socket joint that connects the top of the thigh bone (femur) to the pelvic bone (acetabulum). It is held together by muscles, tendons and ligaments. The inside of the joint has a smooth protective covering of cartilage that assists smooth movement. When the joint is diseased or damaged, this cartilage cushion can wear away, allowing the bone of the head of the femur to rub directly against the acetabulum. This leads to pain, stiffness, limping and muscle weakness.

How is the diagnosis made?

A complete history and physical examination allows the physician to determine any correlation between symptoms of pain with past history and demands that have been placed upon the hip. The physician will enquire about experiencing episodes of trauma or instability, and examine the ligaments and hip alignment. X-rays are used to determine the extent of degeneration to the cartilage or bone and may suggest a cause for the degeneration of the hip joint. Blood tests and joint aspiration (removing a small amount of fluid from the affected hip joint) may be required to rule out systemic arthritis (such as Rheumatoid Arthritis) or infection in the hip if there is reason to believe that other conditions are contributing to the degenerative process.

How do I prepare for a hip replacement?

Preparing for a total hip replacement often begins several weeks prior to the actual surgery. Emphasis is placed upon the individual maintaining good physical health before the operation. Upper body strength becomes important for the ability to use a walker or crutches after the operation.

How is the procedure done?

During surgery, once the hip joint is exposed, the head and neck of the femur are removed. The shaft of the femur is then reamed to accept the metal component consisting of the head, neck, and stem. The acetabulum is then reamed to accept a plastic cup. The ball and socket are then replaced into normal position. Both of these implants can be fastened into the bone with or without special cement.

• Cemented procedure - The cemented procedure utilises a doughy substance mixed at the time of surgery that is introduced between the artificial component and the bone. Depending upon their health and bone density, people over the age of 60 will receive this type of joint fixation.
  
  
• Noncemented procedure - Despite its common use, not all individuals are candidates for a cemented hip. Studies show that young active adults tend to loosen their artificial components prematurely. The current trend therefore, is to use an artificial joint covered with a material that allows bone tissue to grow into the metal. A tight bond of scar tissue is formed, which anchors the metal to the bone. This is called a cementless total hip replacement.

This type surgery is technically more sensitive, requiring a more exact fit of the metal component to the femur. In this procedure, the surface of the metal is prepared with a small porous roughened coat, which attracts bone in growth. This process is called porous ingrowth or osteointegration.

In general, the artificial joint implants used in the non-cemented procedure are larger than those used with cement but are still proportional to the size of the individual bone. Since their introduction, many different devices using cementless fixation have been used with the hope that these implants will maintain their attachment to bone for a longer period of time.

Other types of hip replacement procedures

There are other types of hip replacement procedures:

• Hybrid fixation refers to a procedure in which one component (usually the socket) is inserted without cement, and one component (usually the stem for the ball of the femur) is inserted with cement.
  
  
• Hemi-surface replacement for osteonecrosis. This is one option the surgeon will utilise to minimise tissue reaction. It involves replacing only the diseased part of the joint. A hemi-surface replacement is often recommended for people who have avascular necrosis and have some remaining articular cartilage on the acetabulum. The hemi-surface replacement preserves and maintains bone by providing stress transfer to the femoral neck and upper femur. It can also help avoid inflammatory reaction and joint loosening.
  
  
• Surface replacement of the hip. If the surgeon chooses to do a surface replacement procedure, the neck of the femur is preserved rather than amputated as in conventional stem-type total hip replacement. The femoral head is then reshaped and resurfaced with an artificial or prosthetic shell. When this procedure is used, the femur accepts more of the load (as a normal hip does) and thereby preserves bone. Since the resurfaced head is very similar in size to the normal hip, it proves to be more stable and risk of dislocation is greatly minimised.

What are the risks and complications?

As with all major surgical procedures, complications can occur. Some of the most common complications following hip replacement are:

• Deep venous thrombosis - DVT can occur after any operation, but is more likely to occur following surgery on the hip, pelvis, or knee. Thrombosis occurs when the blood in a large blood vessel of the leg or pelvis forms blood clots; in DVT it is within the veins. DVT may cause the leg to swell, become warm to the touch or become painful.
  
  
• Infection - The chance of getting an infection following hip replacement is less than 1%. Superficial infections involving the surgical incision are easily treated with antibiotics. More serious infections can result from bacteria invading the bone in the presence of metal and cement. Infection can be serious enough to cause the artificial implant to loosen. Some infections may show up very early, even before the discharge from the hospital. Others may not become apparent for months, or even years, after the operation. Infection can spread into the artificial joint from other infected areas.
  
  
• Dislocation - Dislocation has a low incidence of approximately 3%. This can be the result of the individual not being compliant with post-operative restrictions. Dislocation can also result from muscle imbalance and tightness around the hip joint.
  
  
• Loosening - In the cemented hip, a major reason for joint failure is the result of loosening where the metal or cement meets the bone. In the case of the non-cemented joint, the bone itself fails to attach itself properly to the surface of the implant. In either case, loosening of the joint implants will often lead to a total hip revision. Since there are no ligaments to hold the components of the new hip together, a person must be careful in the first few weeks following surgery to avoid positions that could dislocate the hip. However, with time, the body will make enough scar tissue to stabilize the new hip replacement

What you can expect after a hip replacement

New technology involving the implants for artificial hip replacement and advances in surgical techniques has improved the immediate and long-term outcome of the surgery. Generally today's artificial hips can last a lifetime. However, if the person is very young, the plastic can wear out. Fortunately, with the new socket implants for the pelvis, the socket can be changed without removing the other portions of the hip joint. The person with a hip replacement may be able to take part in physical activities that were impossible before surgery.

Most individuals following hip replacement surgery are able to return to work within a month or two of surgery. Yet, some individuals that are exposed to work requiring a great deal of repetitive climbing or crawling, may find it necessary to change jobs. Overall, many find that the activities that were once painful such as climbing up and down stairs, sitting for extended periods of time, and getting in and out of cars can now be performed with less pain.

Patient Services - More on Hip

* Source: Your Medical Source; Hip Diagrams: Australian Orthopaedic Association