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Jury Is Still Out on Hip Resurfacing Arthroplasty

In the short time since hip replacements were first introduced, the procedure has changed and improved in many ways. One of those developments has been the hip resurfacing arthroplasty. Hip resurfacing arthroplasty is a type of hip replacement that replaces the arthritic surface of the joint but removes far less bone than the traditional total hip replacement.

Because the hip resurfacing removes less bone, it may be preferable for younger patients that are expected to need a second, or revision, hip replacement surgery as they grow older and wear out the original artificial hip replacement.

In this review article, surgeons from the UT Southwestern Medical Center in Dallas, Texas bring us up-to-date on the latest information about hip resurfacing. How well do they work? What are the potential problems or complications? First, let's take a look at a little bit of history around this procedure. It was first used in the 1970s, but there were too many hip fractures and the components used didn't hold up.

So, the procedure fell out of favor in the United States. But surgeons in Australia and Europe continued to improve the surgical technique, instrumentation, and implant design. During that time, two generations of hip resurfacing systems have been developed. Since 2006, the Food and Drug Administration (FDA) has approved two different implant systems: the Birmingham Surface Replacement (BSR) System and the Cormet design.

There are some studies now to help us look back and see how effective these implants have been and what problems are still left to deal with. Using data from the 1000s of hips done outside of the United States along with studies done in the states, it's clear that the overall revision rate is still higher for resurfacing than for standard total hip replacements. But the rate is still small enough to make it worth having the procedure for the many patients who aren't ready yet for a complete total hip replacement.

Studies show that women are more likely to have a failed resurfacing procedure. So are patients who've had a previous hip surgery or anyone who has osteonecrosis (loss of blood supply to the top of the femur or thighbone causing death of bone cells). And anyone with inflammatory arthritis or developmental dysplasia of the hip is at increased risk for implant failure.

Based on this information, surgeons are careful when choosing patients for the resurfacing procedure. For example, patients are younger and more often male than female. Anyone who is obese is not considered for the procedure. Patients in good overall health are more likely to receive hip resurfacing. As a result, implant survival is up and complications are down. Rates of re-operations are also lower for surgeons with extensive experience with the hip resurfacing procedure.

So how successful is hip resurfacing compared to a standard hip replacement? Early results suggest that patients receiving hip resurfacing implants have better overall function with greater motion and higher activity levels compared with patients who had a total hip replacement. Patients with hip resurfacing implants also have better waling speed and hip kinematics (movement).

In some ways, it's difficult to compare outcomes of hip resurfacing versus total hip implants. Patients in the hip resurfacing groups tend to be much more active. Many are involved in sports at least four hours a week. Implant survival in both groups is probably affected by activity level (high versus low).

What about complications? How do these compare between the two procedures? Fracture of the femoral neck is the most common problem associated with hip resurfacing. In fact, it's the number one cause of implant failure. Again, studies support the idea that women and obese patients are at increased risk for these types of fractures.

Besides eliminating these patients as potential recipients of the procedure, studies of cadavers (hip specimens saved for study after death) have added some more helpful guidelines. Using different surgical techniques and then loading the specimens until they failed, researchers found that how the implant is placed in the hip makes a difference. Tilting the implant slightly off center (valgus position) reduced the fracture rate considerably.

Other surgeons have focused their attention on the effects of different surgical approaches when resurfacing the joint. They found that using a posterolateral approach (from the back and side) reduces blood flow to the femoral head. Using an anterolateral (from the front and side) approach may yield better results.

Computer-assisted surgery may help improve results with hip joint resurfacing. Computer navigation has the advantage over manual techniques of a more accurate placement of the implant. Getting the best component position costs more, but it might be worth it if the revision rate can be substantially reduced.

And one last concern about hip resurfacing: metal ion release. Because the component parts of the implant are metal, tiny pieces of metal ions flake off and get trapped inside the joint forming a tumor-like cyst or entering the blood stream. This could become a problem for anyone with metal hypersensitivity or for very active adults. Increased activity has been shown to increase ion levels in the blood. As a result, implant failure may require conversion to a total hip replacement.

Is joint resurfacing superior to a standard total hip replacement? That question remains unanswered. The authors conclude that this new technology bears watching. A high-degree of surgeon skill is required, so it's not something every surgeon is going to be able to offer. Computer navigation systems may help further refine the procedure. The jury is still out until safety concerns about metal exposure and the development of pseudotumors are answered.

References: James Phelps, et al. Hip Reconstruction. Current Status of Hip Resurfacing Arthroplasty. In Current Orthopaedic Practice. January/February 2009. Vol. 20. No. 1. Pp. 2-7.

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