Issue: July 2012
July 03, 2012
2 min read

Study supports validity of survivorship findings reported by implant designers

Issue: July 2012
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Research comparing results of hip and knee implants reported by the designing surgeon or center with findings from national registries indicates that outcomes from a designer series are believable.

“There is 32% discordance between the designer series and the registry series,” Hany S. Bedair, MD, said during his presentation at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting. “If you are a half-glass full person, that is 68% with no difference. What is interesting is there were two [designs] that accounted for two-thirds of the discrepancies. If you excluded those for argument’s sake, that means 87% had no difference between the designer series and the registry series.”

Designer implant studies

For their research, Bedair and colleagues questioned the nature of “designer” implant studies sponsored by affiliated surgeons or institutions and whether such studies yielded reliable results.

“A lot of these surgeons are highly experienced in the field. They possess some technical expertise that maybe not all of us do, [and] there are certainly some financial ramifications that we cannot discount,” Bedair, from the Department of Orthopaedics at Massachusetts General Hospital in Boston, said. “Even though we recognize that these biases exist and we accept the studies, [can] we believe that and can we expect these results from everyone? Then there is the issue of intellectual pride and creative prowess. Nobody wants to be affiliated with a failed device.”

Bedair and colleagues compared the designer results of five knee and 10 hip implant devices that also had results in national joint registries from Australia, England, New Zealand, Sweden and Wales. They discovered that 12 of 38 comparisons (32%) showed a higher 5-year survivorship in the designer series than in the registry series.

“What was interesting [was that] eight of these 12 differences were related to two different implants,” Bedair said.

Differences among registries

No design series reported a lower survivorship than the registry series. The investigators found that 60% of the design cases reported survivorship similar to that reported in the registries, while 40% reported higher survivorship than that in at least one of the registries. In studies where 5-year survivorship data was not available, the investigators extrapolated the results.

“We could not find any correlation between the study parameters and a higher concordance rate. Overall, I would say these [designer] results are believable,” Bedair said.

He also noted differences between registry results for implant survivorship.

“When we went back and compared registries to registries, there is a 38% discordance rate,” Bedair said. “If we compare the Australian registry to the English-Wales registry, for example, there is a 75% discordance rate. Between registries, there is certainly some difference.” – by Jeff Craven

  • Bedair HS, Lawless BM, Malchau H. The implant designer series: Are these favorable results believable? Paper #352. Presented at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting. Feb. 7-11. San Francisco.
For more information:
  • Hany S. Bedair, MD, can be reached at the 55 Fruit Street, Boston, MA, 02114; email:
  • Bedair has no relevant financial disclosures.