Joint Replacement Institute

One of the hottest topics today in Orthopaedics is hip resurfacing. It is the fastest growing implant in the world today, and in some countries it has already become the gold standard for the arthritic hip for the patient under 50. A review of our series of patients less than 50 years of age has been published1, and it is included in the new features of this updated website. Resurfacing qualifies as minimally invasive because a stem is not inserted in the femoral canal and because the femoral head and neck are preserved. It is the most tissue-sparing arthroplasty for the hip.

The results of the Conserve®Plus metal-on-metal, hybrid hip resurfacing and other hip resurfacing devices far surpasses the versatility and durability of the earlier generation of metal on polyethylene hip resurfacings of the 70’s and 80’s. My personal experience with the Conserve®Plus, which represents more than 1100 hips over the past ten and a half years, has been very gratifying. The durability of the Conserve®Plus socket has been excellent with no personal cases of loss of fixation or loosening, which parallels my previous experience using this porous bead technology for fixation with other socket systems utilized as early as 1983. On the femoral (other) side the procedure is very technique dependent. The incidence of femoral loosening in patients with primary osteoarthritis and good bone quality has been rare even from the beginning of implantations in 1996. Unlike other hip resurfacing surgeon investigators, I have challenged the system by resurfacing hips in patients with severe cystic changes as long as the patient was young. Overall femoral loosening has occurred in 2% of my patients over this 10.5-year period, and was associated with hips that had risk factors (i.e. large cystic degeneration and/or a small surface area)2,3 and were operated on during our early experience when the instrumentation and technique were being developed. Fifty percent of our problem cases occurred in the first 110 patients. After carefully studying retrievals, we determined that the major reason for failure in these challenging cases was inadequate fixation at the time of surgery. Because the surface area for femoral fixation is small compared to conventional stem-type devices, I have learned that meticulous attention to the preparation of the bone surfaces is critical and that optimizing fixation can likely mean years of increased durability. As a result, technique changes were made to improve the quality of the bone preparation and fixation at the time of surgery. This has resulted in a dramatic decrease in the incidence of loosening as well as the signs of loosening even in the hips with significant risk factors4. This study has been recently published and is abstracted herein.

We have not identified any patient who has had a loosening or has signs of potential loosening in over five years, and there have been no patients revised for loosening in the series of hips implanted over the last six years. The improvement of initial fixation is such that long-term durability is now anticipated with our current technique. Our efforts to improve fixation have continued each operating day, and as a result, patients with risk factors, such as cystic degeneration, can be successfully resurfaced. In addition, for the first time, our results have shown equal durability of resurfacing in hips with secondary arthritis (Slipped Capital Femoral Epiphysis, Developmental Dysplasia of the Hip, Legg-Calvé-Perthes disease, Rheumatoid Arthritis, or Osteonecrosis) to that of primary osteoarthritis.

While high impact activities have not been associated with failure when the bone quality was ideal, very high activity levels have been found to reduce durability when there were deficiencies in bone stock with our early technique. However when hips were operated upon with our newly devised techniques the durability of the resurfaced patients who continued high impact activities has been excellent even with some of the risk factors, but further follow-up is needed to determine the long-term effect of activity on prosthetic durability.

Our research in retrieval studies that led to our surgical technique changes is headed by Dr. Pat Campbell. Her manuscript describing this analysis led to the recently published John Charnley Hip Society Award. The data therein supports our belief that short-term failures (less than 5 years) can be eliminated with a resulting anticipation of long-term durability. This progress in my view now justifies carefully applying the resurfacing technology to older patients even though total hip arthroplasty, when using a big femoral head to obviate dislocation, is a very dependable alternative.

Drs. Schmalzried and Beaulé also continue to be enthusiastic about hip resurfacing while being cautious about extending the indications for patients with bone stock deficiencies and into the older age groups.

Due to very strange anarchism, the FDA approved the BHR device, which had never been implanted in the U.S., based on a single surgeon’s experience and despite the fact that the two statisticians on a recommendation panel of five found the supporting data inadequate for approval. The data presented were in stark contrast to the detailed data showing the safety and efficacy of the Conserve®Plus as requested by the FDA and provided by our multi-center IDE surgeons. An IDE study is the only possible avenue open to U.S. products to obtain approval of a Class III device which includes MM hip resurfacing. This has been a very frustrating experience for all of us, including our patients and other site investigators involved in the Conserve®Plus IDE study, which was closed over a year ago. Wright Medical Technology (WMT) has literally spent millions of dollars tracking patients and collecting data on the nearly 2,000 cases for the FDA, and is proceeding with its efforts to accomplish "timely" approval by the FDA for use in the United States.

In my view, this study represents the most comprehensive study ever conducted with solid scientific peer-reviewed evidence of safety and efficacy. It is not surprising that orthopaedic surgeons are overwhelmingly disappointed by the performance of the FDA as cited in a recent survey conducted by CEI, which assessed the opinion of orthopaedists. A link is provided for your information.

http://www.cei.org/gencon/025,05732.cfm

The good news is that the Conserve®Plus, which in fact is a year older than both of the British devices, (the BHR and the recently approved Cormet), provides several advantages over those two and remains in our opinion the best device with improvements herein (see enclosed comparison chart). These advantages are outlined for your reference and further study.

While no definite date has been given, it has been rumored that the Conserve®Plus will probably be approved in the near future. The Conserve®Plus System is available everywhere else in the world where WMT has submitted application for approval. A bevy of other devices are in the pipeline with every major manufacturing company having one in development. The results of these new devices will have to be evaluated over a ten or more year period to learn of any potential advantages and disadvantages they could present.

On a very positive note, I end this message with the news that our book on “Hip Resurfacing” has just been completed. The book is comprehensive and chronicles the development, indications, operative technique, and results of modern resurfacing including complications and methods of prevention as well as disease-specific experience. This volume is to be published by Elsevier by early 2008.

While I am now concentrating only on hip resurfacing and other hip arthroplasty, both Dr. Schmalzried and Mynatt here at the JRI continue to apply the latest technology in knee resurfacing in their orthopaedic practices.

Harlan C. Amstutz, M.D.