Dr. Rahul Damle – Hip Pain & Hip Revision Surgery Specialist
Over the past 20 years, artificial hip replacements have become increasingly common. Millions of people have gotten a new hip joint. The first time a joint is replaced with an artificial joint, the operation is called a primary joint replacement. As people live longer and more people receive artificial joints, some of those joints begin to wear out and fail. When an artificial hip joint fails, a second operation is required to replace the failing joint. This procedure is called a revision arthroplasty.
Why do revisions become necessary?
The most common reasons that a revision needs to be done are
1. Mechanical loosening
2. Infection in the joint
3. Fracture of the bone around the joint
4. Instability of the implant
5. Wear of one or more parts of the implant
6. Breakage of the implant
Mechanical Loosening / Aseptic loosening
Mechanical loosening means that for some reason (other than infection) the attachment between the artificial joint and the bone has become loose. There are many reasons why this can occur. It may be that, given enough time, all artificial joints will eventually become loose. This is one reason that surgeons like to wait until absolutely necessary to put in an artificial joint. The younger you are when an artificial joint is put in, the more likely it is that the joint will loosen and require a revision.
If an artificial joint becomes infected, it may become stiff and painful. It may also begin to lose its attachment to the bone. An infected artificial joint will probably have to be revised to try to cure the infection.
The surgery may be a one-stage exchange or more often a two-stage exchange.You may be needed to be placed on antibiotics for several weeks or months after the exchange operation.
A fracture may occur near an artificial joint. It is sometimes necessary to use a new artificial joint to fix the fracture. For example, if the femur (thighbone) breaks right below the stem of an artificial hip, it may be easier to replace the femoral part of the artificial joint with a new joint with a longer stem to hold the fracture together while it heals, similar to fixing the fracture with a metal rod.
Instability means that the joint dislocates (the metal ball slips out of the plastic socket). This is very painful when it happens. If it happens more than once, it’s time to consider revising the artificial hip joint to keep it from coming out of joint.
As surgeons have become better at understanding how to put in an artificial joint so that it does not loosen as fast, we have begun to see actual wear of the plastic parts of the artificial joints. In some cases, if the wear is discovered in time, the revision may only require changing the plastic part of the artificial joint. If the wear continues until metal is rubbing on metal, the whole joint may need to be replaced.
Finally, another type of wear can occur that breaks the metal due to the constant stress that the artificial joint undergoes everyday. In weight-bearing joints such as the hip, this is greatly affected by how much you weigh.
The Revision Prosthesis
There are two major types of revision implants:
1. Cemented prosthesis
2. Uncemented prosthesis
A cemented prosthesis is held in place by a type of epoxy cement that attaches the metal to the bone.
An uncemented prosthesis has a fine mesh of holes on the surface that allows bone to grow into the mesh and attach the prosthesis to the bone.
Both are widely used in revision hip surgery. In some cases, a combination of the two types is used in which the ball portion of the prosthesis is cemented into place, and the socket not cemented. The decision about whether to use a cemented or uncemented prosthesis during the revision surgery is usually made by the surgeon based on your age, your lifestyle, and the surgeon’s experience.
Each prosthesis is made of two main parts. The acetabular component (socket) replaces the acetabulum. The acetabular component is made of a metal shell with a plastic inner liner that provides the bearing surface. A special type of acetabular component may be used during the revision surgery. This is because the bone of the pelvis may have worn away somewhat since the initial replacement was done. The bone may be weaker, or areas of the bone may be missing. These special components are designed to spread the weight across a wider area on the acetabulum. They attach to the stronger bone outside the area of wear and tear.
The femoral component (stem and ball) replaces the femoral head. The femoral component is made of metal. Sometimes, the metal stem is attached to a ceramic ball.
There are special types of revision stems as well. This is because the bone of the femur is usually not the same as when the initial replacement was done. The bone may be weaker, or areas of the bone may be missing. A longer stem can reach further down the femoral shaft and distribute your body weight better.
Revision joint replacements are much different from primary joint replacements.
One reason that revision procedures are not routine is that there is almost always bone loss around the primary prosthesis. The surgeon deals with this problem by placing a bone graft or some other material around the artificial joint to reinforce the bone. This bone graft maybe an autograft or allograft
When the primary artificial joint has been put in using cement, the cement has to be removed from the socket of the hip as well as from the femoral canal (the bone marrow space in the thighbone).
Because the bone is often fragile and the cement is hard, removing the cement sometimes can lead to a fracture of the femur during the operation. This is not unusual, and in most cases the surgeon will simply continue with the operation and fix the fracture as well. In some cases, the femur must be broken open to remove all the cement and the artificial joint. This is one reason that revisions are challenging.
Limitations of Revision Hip Replacement
A revision joint replacement of the hip is more complex and unpredictable than a primary joint replacement. Since many factors can influence its longevity, your surgeon will not be able to say exactly how long your revision will last. Also, keep in mind that because revision surgery is more complicated than primary joint replacement, it may take up more time than a primary surgery to be able to perform your routine daily activities. Often people continue to need a walking aid because knee pain increases when they are on their feet for prolonged periods. There is also a greater chance that the hip will be tight and unable to bend all the way after hip revision surgery.
In some cases, if an artificial joint fails, it may not be possible to put another artificial joint back in. This can occur if the primary joint has failed because of an infection that cannot be controlled, if the bone has been destroyed so much that it will not support an artificial joint, or if your medical condition will not tolerate a major operation.
Sometimes a choice other than hip revision is best because a big operation might result in a failure or even death. Removing the prosthesis and not replacing it doesn’t mean the patient can’t walk anymore. The surgeon may suggest an excision hip arthroplasty.
As with all major surgical procedures, complications can occur.
Some of the most common complications following revision arthroplasty of the knee include
1. Medical / Anaesthesia complications
2. Thrombophlebitis / DVT
5. Dislocation & Instability
6. Incision & wound complications