An Industry Anniversary

May 9, 2008, marked a significant orthopedic anniversary—the second year since the FDA approved the first hip resurfacing product for use in the United States. As is true at the beginning of most relationships, surgeons were hopeful and expectant about working with the new device. But after two years of experience, are orthopedists still happy with their hip resurfacing relationship?

The product that started it all in the U.S. was, of course, Smith and Nephew’s BIRMINGHAM HIP™ Resurfacing System (BHR™), which gained FDA approval in 2006. Since that time only one other product in this space has gained FDA approval—the Corin Group’s Cormet™ Hip Resurfacing System marketed by Stryker Corporation.

Surgeons in Europe were implanting the BHR as early as 1997, giving U.S. surgeons almost a decade in which to observe and build up expectations prior to the FDA approval.

Among the expectations for the hip resurfacing procedure were:

• A 98% success rate (less than 2% revised).
• A length of stay of three to five days, or significantly less than that typically required for total hip replacement.
• Fewer dislocations than with total hip replacements.
• Decreased amounts of pain throughout recovery.
• Shorter recovery times as compared with total hip replacement.
• Bone preservation.
• Increased time before a patient would require a total hip replacement.

BIRMINGHAM HIP™ Resurfacing System, courtesy of Smith & Nephew, Inc.

How has the BHR lived up to expectations in the United States? Using the PearlDiver database containing over 116 million patient records of 6.99 million patients, a sample was created to compare actual results to the expectations for the BHR. The sample consisted of 324 patients who had the hip resurfacing procedure performed between May 9, 2006, and June 30, 2007.

The first comparison was against the expected success rate of the BHR. The expectation at the time of FDA approval was for a success rate of 98%. Of the 324 patients in the sample, seven had procedures that proved to be unsuccessful, resulting in the BHR being converted to a total hip replacement. The resulting failure percentage of 2.16% is less than the experience reported in the Australian Registry but very close to the U.S. expectations.

A closer examination of the seven patients reveals why the hip resurfacing was converted to a total hip replacement.

• Two patients were given a total hip replacement after being diagnosed with dislocation of the prosthetic joint.
• One patient had a mechanical loosening of the prosthetic joint.
• One patient was diagnosed with an unspecified mechanical complication.
• Three patients were found to have other non-prosthetic complications that affected the outcome of the hip resurfacing procedure.

The second comparison was made against the expectation of a shortened length of stay in the hospital with BHR versus a total hip replacement. The U.S. expectation was that, with BHR, the patient’s length of stay in the hospital would range between three and five days and would be significantly shorter than the average length of stay for a total hip replacement. The results for our sample, since the approval of the BHR through June 30, 2007, are shown in Table 1.

Table 1: Average Length of Stay (in Days), Hip Resurfacing and Total Hip Replacement

The results are good news for hip resurfacing. The average length of stay for both male and female patients never goes above 3.39 days. By the second quarter of 2007, male patients were staying in the hospital at the low end of the time frame at 3.02 days.

While the hospital stay for a patient undergoing BHR is short and within the time of the original expectations, it is not all that much shorter than the length of stay for a total hip replacement. In 2004 the PearlDiver database shows that the average hospital stay for a female patient having a total hip replacement was 4.33 days, considerably longer than the 3.29 days for a female patient undergoing hip resurfacing in the second quarter of 2007. However, since 2004, the average length of stay for a total hip replacement has been shortened to the point that, by the second quarter of 2007, a female patient getting a total hip replacement was staying in the hospital an average of only 0.37 days longer than a female hip resurfacing patient.

The third expectation of hip resurfacing was that, because the hip resurfacing procedure uses a larger ball and socket, there would be fewer dislocations than occur in a total hip replacement. Using PearlDiver data, quarterly samples of patient dislocation data were created for both procedures, as shown below in Table 2. The figures represent the number of patients that had the procedure in a given quarter, and then went on to  experience a dislocation at any time after the procedure.

Table 2: Yearly Dislocation to Procedure Ratios

It appears that, in the short term, a patient is less likely to have a dislocation after hip resurfacing than after a total hip replacement. However, as time passes, the advantage that hip resurfacing holds in the early stages disappears. As shown in Table 2, while only 0.8% of the patients who had the hip resurfacing procedure in the second quarter of 2007 suffered a dislocation, those for whom more time had passed between the procedure and the end date of the sample set—such as those who had a procedure in the fourth quarter of 2006—actually had a higher percentage of dislocation than those who had a total hip replacement..

As the number of hip resurfacing procedures performed in the U.S. increases, it will be interesting to see if this continues. It is important to keep in mind that hip resurfacing has been available in the U.S. market for only two years. As time passes and the market grows, this may change.

But how much market growth can be expected? An examination of the PearlDiver data of patients who underwent a total hip replacement from 2004 through the second quarter of 2007 reveals most would not have qualified for the hip resurfacing procedure. These included patients who had infections, not fully grown bones, blood vessel disease, muscle-related disease, nerve- and muscle-related disease, avascular necrosis, multiple fluid-filled cavities (cysts), impaired kidney function, metal sensitivity, HIV, or AIDS; were females of child-hearing age, or were overweight. The hip resurfacing procedure is also typically performed on males under the age of 65 and females under the age of 55.

When the 17,777 patients in the PearlDiver database who had total hip replacements from 2004 through 2Q07 were analyzed to see how many would have qualified for a hip resurfacing procedure had it been available to them, 2,561, or just 14.4%, fell within the criteria for hip resurfacing. In 2005 alone, 238,130 patients had a total hip replacement, according to the American Academy of Orthopaedic Surgeons’ Facts on Hip Replacements web publication (http://www.aaos.org/Research/stats/Hip%20Facts.pdf). Had the hip resurfacing procedure been approved at that time, 34,290 patients would have qualified. By the end of the second quarter of 2007, only 7.8% of potential patients were having hip resurfacing instead of a total hip replacement. Much of the market remains to be captured.

One reason for the slower growth of hip resurfacing in the marketplace is that the procedure is more complex than a total hip replacement, and surgeons performing it require additional training. Around 1,000 surgeons have been specifically trained for the BHR procedure but only about half are performing the procedure on a regular basis. Patients are reluctant to have the operation performed by a doctor who does only a dozen or so resurfacing procedures a year.