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Improved materials, techniques for hip resurfacing may correct past problems
Better intraoperative guides help surgeons position components and avoid notching.
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Although the first generation of hip surface replacements preserved femoral bone, many surgeons abandoned the procedure because of wear debris, osteolysis, and failures due to femoral neck fractures and component loosening.
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However, there has been a resurgence in hip resurfacing during the last decade. According to Edwin P. Su, MD, the modern generation of metal-on-metal hip resurfacing has improved upon the problems of the past through better implant designs and materials, instruments and surgical techniques.
“This has lead to improvement in the survival curve at [the] mid-to early-follow-up to about 97%” he said during his presentation at the 25th Annual Current Concepts in Joint Replacement Winter Meeting.
Design, materials
While there are more than 10 different hip resurfacing devices available internationally, Su noted that most designs incorporate a femoral component with a short stem for femoral cement fixation and press-fit acetabular fixation.
“With regards to the stem, I think that is important,” he said. “[With] the old Tharies (Zimmer), you could implant the device in and just at the very end, even if your bone preparation was perfect, it would cant into a little bit of varus and that would lead to a stress riser. Whereas with the neck stem, it will guide it down into the proper orientation leading to better biomechanical properties.”
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Image: Beadling L, Orthopedics Today |
Su noted that the implant materials have also improved, and that metal-on-metal devices eliminate the problem of polyethylene debris. “There is a better understanding for metallurgy and that there is a need for high carbide cobalt chromium bearing materials,” he said. “The manufacturing tolerances themselves have also been improved.”
In addition, surgeons now have better instruments for performing hip resurfacing. “Although the surgeons of the past did understand the concepts of preparing the bone and putting it into slight valgus orientation, they had a limited ability to do that with the instruments of the day,” Su said. Today, surgeons have various component sizes which allow them to save bone on both the femoral and acetabular sides.
Instrumentation
“With regards to the instrumentation, a lot of the preparation of the first generation of resurfacing was done freehand and now [we] are using cannulated instruments which basically allow us to precisely prepare the bone reproducibly,” Su said.
He also noted that intraoperative guides have improved and incorporate devices to measure and align the femoral neck. These guides also help surgeons achieve accurate component position and avoid notching the femoral neck.
“I also think that there are improved surgical techniques,” Su said. “There is a better understanding of the blood supply of the femoral head based on work from Dr. Ganz.” The development of suction vents has also helped surgeons create a bed for cementation.
“Overall, I think that there are many improvements that have made surface replacement right this time around,” Su said. “However, none of them are able to overcome what is most important of all, which is surgical positioning.”
For more information:Reference:
- Edwin P. Su, MD, can be reached at Hospital for Special Surgery, 535 East 70th St., New York, NY 10021; 212-606-1128; e-mail: sue@hss.edu. He is a consultant for Smith & Nephew, which also provides research support to his institution.
- Su EP. Surface replacement: Getting it right this time around. Paper #42. Presented at the 25th Annual Current Concepts in Joint Replacement Winter Meeting. Dec. 10-13, 2008. Orlando, Fla.