Primary & Revision Hip Replacement

There are two main types of hip replacement operation, but a number of different components and surgical techniques may be used.

Total hip replacement

In a total hip replacement, part of the thigh bone (femur) including the ball (head of femur) is removed and a new, smaller artificial ball is fixed into the rest of the thigh bone. The surface of the existing socket in the pelvis (the acetabulum) is roughened to accept a new socket component that will join up (articulate) with the new ball component.

Many artificial joint components are fixed into the bone with acrylic cement. However, it’s becoming more common, especially in younger, more active patients, for one part (usually the socket) or both parts to be inserted without cement. If cement isn’t used, the surfaces of the implants are roughened or specially treated to encourage bone to grow onto them. Bone is a living substance and, as long as it’s strong and healthy, it’ll continue to renew itself over time and provide a long-lasting bond. Where only one part is fixed with cement, it’s known as a hybrid hip replacement.

The replacement parts can be plastic (polyethylene), metal or ceramic and are used in different combinations:

  • Metal-on-plastic (a metal ball with a plastic socket) is the most widely used combination.
  • Ceramic-on-plastic (a ceramic ball with a plastic socket) or ceramic-on-ceramic (where both parts are ceramic) are often used in younger, more active patients.
  • Ceramic-on-ceramic (aceramic ball with a ceramic socket) is very occasionally used in younger, more active patients.
Revision Hip Replacement

When this occurs, your doctor may recommend that you have a second operation to remove some or all of the parts of the original prosthesis and replace them with new ones. This procedure is called revision total hip replacement.

Although both procedures have the same goals—to relieve pain and improve function and quality of life—revision surgery is different than primary total hip replacement. Revision hip replacement is a longer, more complex procedure. It requires extensive planning, as well as the use of specialized implants and tools, in order to achieve a good result.

When Revision Total Hip Replacement Is Recommended

Implant Wear and Loosening

In order for a total hip replacement to function properly, an implant must remain firmly attached to the bone. During the initial surgery, the hip replacement components were either cemented into place or were “press fit” into the bone to allow bone to grow onto them. Sometimes, however, bone may fail to grow onto press-fit components. In addition, cemented or press-fit components that were once firmly fixed to the bone can eventually loosen, resulting in a painful hip.

The space around the femoral stem indicates that the component has loosened from the underlying bone.

Wear of the plastic liner (red arrow) and osteolysis (yellow arrow) have caused the acetabular cup to loosen. The femoral head (ball) is no longer centered in the cup.The cause of loosening is not always clear, but repetitive high-impact activities, excessive body weight, and wear of the plastic liner between the ball and the metal cup are all factors that may contribute.

Infection

Infection is a potential complication of any surgical procedure, including total hip replacement. Infection occurs when bacteria attach in and around the surface of the prosthesis. Infection may occur while you are in the hospital or after you go home. It may even occur years later.

If a total hip replacement becomes infected, it can be painful and the implant may begin to lose its attachment to the bone. Even if the implant remains properly fixed to the bone, there may still be pain, instability, and drainage from the infection. Because bacteria cannot be easily eliminated from a joint replacement with antibiotics alone, revision surgery is usually necessary.

Revision surgery for infection can be done in different ways. To determine which procedure is best for you, your doctor will consider a number of factors, including:

  • The type of bacteria
  • The duration and severity of the infection
  • Your preference for a specific treatment

Debridement. In this procedure, your doctor will open up your hip, wash out the bacteria, and exchange the ball and plastic liner. The metal implants that are firmly attached to the bone are left in place. After debridement, you will receive intravenous antibiotics for several weeks to help cure the infection.

Staged surgery. In some cases, the implants must be completely removed. If the implants are removed to treat the infection, your doctor will usually perform the revision in two separate surgeries.

In the first surgery, your doctor will remove the implants and place a temporary cement spacer in your hip. This spacer is treated with antibiotics to help fight the infection and will remain in your hip for several weeks. During this time, you will also receive intravenous antibiotics.

When the infection has been cleared, your doctor will perform a second surgery to remove the antibiotic spacer and insert a new prosthesis. In general, removing the implant leads to a higher chance of curing the infection, but is associated with a longer recovery.

In some cases, your doctor may be able to remove the implants, wash out the hip, and place a new prosthesis all in the same operation. This procedure, which is called a one-stage exchange, may be appropriate in limited situations.

Recurrent Dislocation

A hip replacement has a ball-and-socket structure like that of your natural hip. For a hip replacement to work well, the ball must remain inside the socket. Trauma or certain hip positions can sometimes cause the ball to become dislodged from the socket. This is called a “hip dislocation.” If you experience recurrent hip dislocations, you may need revision surgery to better align your hip joint or to insert a special implant designed to prevent dislocations.

(Left) Dislocation after primary hip replacement. (Right) The revision implant is designed with a ring mechanism that locks the femoral head (ball) into the socket to prevent dislocation.

 

Fracture

periprosthetic fracture is a broken bone that occurs around the components of an implant. These fractures are most often the result of a fall, and often require revision surgery. To determine whether a revision is needed, your doctor will consider several factors, including the amount of remaining bone, whether your implant is loose, and the location of the fracture.

In rare circumstances, an implant itself can break. This also requires revision surgery.

(Left) This patient has a periprosthetic fracture of the femur (thighbone). (Right) The same fracture after treatment with revision surgery.

Reaction to Metal Ions and Allergy to Metal

Over time, the metals used in implants can break down or wear, causing tiny particles to fall off the device into the space around the implant. This is more common with “metal-on-metal” devices, in which both the ball and socket components are made of metal. In some patients, sensitivity to the metal ions in these particles can result in damage to the bone and soft tissues around the hip and lead to the need for revision surgery.

In very rare cases, a patient allergy to the metal used in implants may cause pain around the site of the implant. There is no definitive agreement among doctors regarding metal allergy in this setting, however, and more studies are needed.