Yes, Virginia, You Can Resurface Hips

The hip resurfacing debate keeps raging. This technology category has had a target on its back since that warm day in September 2005 when the Orthopedics Advisory Committee voted 4 to 2 to recommend commercialization of the Birmingham Hip Resurfacing (BHR) system in the United States.

With the committee vote in hand, the FDA approved the BHR (marketed by Smith & Nephew) for U.S. sales eight months later. What surprised observers at the time and, we think, laid the foundation for today’s debate was that the data set used by the Orthopedics Advisory Committee and the FDA to approve the BHR came from a retrospective study of, in effect, 124 X-rays. No randomized, blinded controlled prospective trial data.

Standing behind those 124 X-rays were, however, roughly 2, 400 patients and documented revision rates that were essentially the same as traditional total hip replacements (THR). In the study, the method employed to determine patient outcomes was a telephone interview.

Conserve Plus- Total Resurfacing Hip System / Source: Wright MedicalWhy did the FDA approve the BHR on such comparatively light data? It is probably not an exaggeration to say that the FDA felt some pressure based on the European data to approve the first hip resurfacing system for the United States. At the time, hip resurfacing procedures were fairly common in Europe, Canada and Australia. In fact, hip resurfacing has been performed outside the U.S. since 1997. By 2009, we estimate, more than 90, 000 patients have received a hip resurfacing worldwide.

But that was only part of the story. The FDA asked for ten years of follow-up study when they approved the BHR in 2005. It didn’t take ten years. Data is streaming out from various studies now. They are confirming that hip resurfacing, is appealing for patients and surgeons alike, but they are also showing that hip resurfacing has some serious caveats—particularly regarding which prosthesis are employed in which patients.

At last month’s AAOS (American Academy of Orthopedic Surgeons) annual meeting, Drs. Graves, Steiger, Davidson, Ryan, Miller, Standord and Tomkins provided the results of their eight-year follow up of 12, 093 primary hip resurfacing procedures. Their conclusion:

Outcomes of resurfacing hip replacement is very dependent on both patient and prosthesis selection.

The researchers measured time to first revision using the Kaplan-Meier scale and, trumpets please:

1. Best results were achieved in male patients less than 55 years of age with a diagnosis of osteoarthritis and who required a femoral resurfacing component which is 50mm or greater in size. In this group the rate of revision for resurfacing hip replacement is comparable to primary total hip replacement.

2. Worst results were achieved in women of all ages who were diagnosed with anything other than osteoarthritis (in particular DDH) and received a femoral resurfacing component of less than 50mm in size had a significantly increased risk of revision.

3. Finally, but most importantly and certainly to fuel this debate further, there was considerable variation in risk of revision depending on the type of prosthesis (we added the emphasis). And the three most used prostheses in the study were the BHR (Smith & Nephew), ASR (DePuy) and the Durom (Zimmer).

However, as we discovered when we looked into this debate, the two most studied hip resurfacing systems in the United States are the BHR and Wright Medical’s CONSERV Plus. The BHR was the first hip resurfacing system approved in the U.S. Fourteen months after the BHR was approved, the FDA gave Corin Group’s hip resurfacing system the green light for the U.S. Conserve Plus was originally available in the U.S. (before BHR) as a large femoral head component. In 2009 it was approved for hip resurfacing.

Source:  Wright Medical Corporation

Hip resurfacing is an alternative to total hip replacement . It has several advantages including less bone removal, potentially (and more about this later) fewer hip dislocations because of the larger femoral head size and, if a revision is required, potentially easier revision surgery since the surgeon has more bone stock to work with.

What could go wrong with hip resurfacing? Number 1 on the hit list is femoral neck fractures (rate of 0-4% according to the literature) followed by aseptic loosening, metal wear and squeaking.

Hip resurfacing is supposed to be for younger patients who have non-inflammatory degenerative joint disease, do not have an infection, and are not allergic to metals. The goal of hip resurfacing is to facilitate a more active post-operative lifestyle. The large size cap and cup are roughly the same size as a person's original femur bone and could reduce or even prevent dislocations.

Then we found this study by Dr. Koen De Smet who’d performed roughly 3, 000 hip resurfacing procedures since 1998 and had used the following prosthetic devices:

Source:  Dr. Koen De Smet, ANCA Medical Centre, Ghent, Belgium

Dr. De Smet has been retrieving BHRs, Conserves and other components for several years and sending them out for wear measurements. He found that:

1. The BHR had “high wear; average of 60 microns on the femoral side, 53 microns on the acetabular side, n=17”.

2. The Conserve Plus had almost no wear data since acetabular malposition (a common reason for revision and therefore component retrieval) was rarely seen with this implant. But where the components were sent to the lab for testing on a coordinate measuring machine, the Conserve Plus had wear rates of 7.03 +/- 13.5 microns while the BHR had 54.7 +/- 49 microns of wear.

De Smet then measured the abduction angle, ion wear rates and on and on and on for the different components.

Bottom line: he found a clear performance difference between devices and attributed most of the difference to a greater and more forgiving head coverage angle (Wright Medical’s Conserve Plus) and 2mm size increments (BHR is at 4mm size increments in the U.S., 2mm in Europe and elsewhere).  

Here is his summary table which, since most of his experience was with the BHR and the Conserve Plus, only deals with those two implants.

Source:  Dr. Koen De Smet, ANCA Medical Centre, Ghent, Belgium

According to De Smet’s data, the Conserve Plus delivered significantly lower post-op complication rates including almost no squeaking.

Late in 2009, the AAOS Board of Directors approved a new technology overview (TO) study regarding hip resurfacing (HR) which was led by Kristy L. Weber, M.D., chair of the Council on Research, Quality Assessment and Technology. Here is a quick summary of their conclusions (details are on the AAOS website):

“Resurfacing arthroplasty is now offered worldwide as a treatment option in some cases of end-stage hip arthritis.” Modern total hip resurfacing implants have attempted to address many of the shortcomings of early resurfacing devices by incorporating cementless fixation principles on the acetabulum with material and manufacturing improvements to produce a durable, low-wear bearing surface.

The workgroup reviewed 786 hip resurfacing citations, 3, 056 total hip prognostic citations, and data from seven joint registries.

Revision Rates

Based on data from three of those registries, patients who’d received HR are at greater risk for revision than patients who receive total hip arthroplasty (THA). The Australian registry, however, suggests that younger males with osteoarthritis might have a lower revision rate after HR than THA.

The workgroup also concluded that the literature does not conclusively demonstrate predictors of better or worse patient-oriented outcomes (such as pain relief, patient satisfaction, or walking ability) for either resurfacing arthroplasty or THA.

And then, looking at a direct comparison between HR and THA, the workgroup concluded that the disparate preoperative hip function scores and demographic characteristics between the groups enrolled in the relevant comparative studies “prohibit meaningful comparisons and confound the interpretation of the data.”

Improving Outcomes

As to which technique, THA or HR, delivered better outcomes; the workgroup looked only at formal studies, not anecdotal reports. The group could only find low-quality studies and those studies suggested that outcomes after hip resurfacing can be improved by changes in technique and increased surgeon experience.

After literally tens of thousands of patients, there is little debate, we think, about the appealing aspects of hip resurfacing. Compared to all-cemented, large head components of the early 1990s, newer metal-on-metal components are showing better long-term wear.

But debates around hip resurfacing rage on. Lest three key points get lost in the din, here they are again:

1. Hip resurfacing works and can be routinely successful for BHR, Conserve Plus and other products

2. BUT…different components have different outcomes independent of surgeon training or experience and from the data it appears that Wright Medical’s Conserve Plus is posting up the better scores

3. Patient selection is huge and may be as important as component selection

For more information we refer our readers to the AAOS site and the plethora of papers submitted over the past three years at its annual meetings.