Surgeons question the cost-to-benefit ratio of new premium knee implants
Surgeons question whether the benefits of premium knee implants outweigh the extra costs (Cover Story @ OrthoSuperSite)
Premium knee implants, such as mobile-bearing and high-flexion knees, were created to address specific patient needs and provide the function that today’s younger, more active patient desires. But whether these premium implants provide greater longevity than their standard lower-cost counterparts remains to be seen in the literature.
With many of these premium implants being on the market for as few as 5 years, some surgeons note that the necessary long-term data on these designs are not yet available.
“The concept of a premium knee is to improve the longevity of total knees and to improve the function,” Michael Kelly, MD, chairman of orthopedic surgery at Hackensack University Medical Center in Hackensack, N.J., told Orthopedics Today. “Surgeons like the versatility . . . The more premium knee sometimes offers more sizes [and] more adaptability to a given knee.”
“Premium implants offer the surgeon increased flexibility to deal with challenges that are unique perhaps to the particular patient that he or she may be dealing with,” Adolph Lombardi Jr., MD, FACS, of Mount Carmel New Albany Surgical Hospital in New Albany, Ohio, told Orthopedics Today. “All technology unfortunately comes with a price, but we feel that there are often times when we need some of the enhancements that have been generated by these types of implants.”
Michael Kelly, MD, said the aim of premium knees is to improve function and implant longevity. He noted that studies to date have shown no significant differences in range of motion and longevity with high-flexion and mobile-bearing knees.
Image: Hackensack University Medical Center/Steve Hockstein
However, “the fact remains that it is difficult to make a decision based on science where there is no science,” A. Seth Greenwald, DPhil (Oxon), director of Orthopaedic Research Laboratories in Cleveland andOrthopedics Today Editorial Board member, said.
The number of premium implants used for total knee arthroplasty (TKA) appears to be increasing. In a recent study published in Clinical Orthopedics and Related Research (CORR), Terence J. Gioe, MD, chief of orthopedic surgery at the Minneapolis Veterans Affairs Medical Center, and colleagues found that the use of premium implant TKAs increased sixfold between 2001 to 2004 and 2005 to 2008, while use of standard implants decreased slightly.
Surgeons and patients choose to use premium implants because of their potential for increased longevity and functional improvements.
“Premium implants, in my mind, are trying to improve the functional result that a patient now desires,” Kelly said. “In 1980, patients were happy to be rid of their pain and to get 90· to 100· of motion, [and] go up and down the stairs if they could. Well, that’s not today’s patient.”
Kelly said today’s patient is younger, more active and more demanding of the quality of the TKA — “they want the range of motion even if they don’t use it all the time,” he said.
Kelly said that although some believe that high-flexion knees were designed to provide more motion, that is not the case.
“What the high-flexion knees have been designed to do is allow a ‘flexion-friendly’ environment, meaning that for those patients who are able to gain these extremes in range of motion … these implants are designed to allow that flexion to be less injurious to the knee itself,” Kelly said. “The relationship between the femoral component, tibial component and tibial plastic is one that has been manicured to allow this range of motion safely without necessarily putting the knee at risk for edge loading or deleterious effects that a large amount of flexion might have on the older designs.”
Another new technology that comes with an extra cost is patient-specific knee instruments, according to Lombardi. With these instruments, the surgeon generates a 3-D image or model of the knee to produce a planning algorithm, which allows him or her to perform a virtual surgery on the computer and then adjust the positioning of the guide and bone cuts. Research on cadavers and radiographic analyses conducted by Lombardi and colleagues published or scheduled for publication in CORR and Orthopedics have shown equal if not superior results with these guides compared with traditional instruments, Lombardi said.
“One of the things we know about the standard instruments is that there is a little bit of a margin for error in positioning these implants, and we know that if the implants are not positioned accurately, there is early failure from malalignment,” he said.
As more surgeons embrace the technology and manufacturers become better at producing these guides, Lombardi said he believes that the cost of the technology will decrease.
Early to midterm results
Gioe’s community registry study published in CORR revealed early to midterm results, which demonstrated no difference in revision rates between standard and premium implants, including mobile-bearing and high-flexion designs and designs using oxidized zirconium femoral components or moderately crosslinked polyethylene inserts.
Gioe and colleagues compared 3,462 standard TKAs to 2,806 premium TKAs from the HealthEast Joint Registry, a community-based total joint registry in the St. Paul, Minn., metropolitan area. At an average follow-up of 3.4 years (range 0 to 8 years), the researchers found no difference in cumulative revision rates between standard and premium TKAs. They also found that the premium implants cost approximately $1,000 more than standard implants.
“What this paper shows is that in this time frame, despite their greater expense, premium implants don’t survive any better,” Gioe told Orthopedics Today. “However, having said that, what is unknown is whether the price difference will be offset by improved survival with longer follow-up.”
Gioe also said out that “a number of early revisions are more surgeon dependent than design dependent. Regardless of what designs we use, we’re going to see a certain percentage of failures from instability or infection … Surgeons clearly want the best for their patients, but we have to do a better job over time of defining what is best. Clearly, it’s not always the most expensive implant.”
Leo Pinczewski, MD, of North Sydney Orthopaedic and Sports Medicine Center in North Sydney, Australia, expressed some reservations regarding Gioe’s study and said that, “It’s just over a short period for joint replacement, and it is a study with the only outcome coming from a joint registry, which collects very little data on the prostheses.”
Gioe and his colleagues acknowledge the limitations to their study, including the short follow-up due to the recent introduction of some of the premium implants; the inability to identify patients who had clinical failure or poor functional results, or those who may have benefited from better functional results with a premium implant; and the fact that some of the patients may have had revision surgery elsewhere.
Greenwald gave credit to the study for using a single registry with data reported by general orthopedic surgeons who were not developers or consultants.
Studies that have evaluated the functional results of premium vs. standard implants have also demonstrated similar results between the prostheses.
“In virtually every study that has been done to date, … these kinds of designs are not making a difference with regards to functional results as well,” Gioe said.
For example, Gioe and colleagues published a randomized controlled trial of a mobile-bearing TKA design vs. the fixed-bearing variant and were not able to show any difference between the prostheses for range of motion, pain relief or Knee Society scores (KSS) at a minimum follow-up of 2 years (mean 42 months). According to Gioe and colleagues, other studies, including those by Minoda, Ries and Rodriguez, have not definitively proven whether moderately crosslinked polyethylene inserts provide improved function or survival.
Kelly added: “There are several articles out there that have compared a variety of different types of high-flexion knees … and even mobile-bearing knees, and none of the articles to date have demonstrated significant difference in range of motion or longevity.”
However, last year in Orthopedics, Crow and colleagues reported a statistically significant improvement in postoperative range of motion with posterior cruciate-retaining TKAs using high-flexion inserts compared with standard knee prostheses, and claimed that their study was the first report to find an improvement in flexion with high-flexion inserts.
According to Kelly, no study to date has shown a greater benefit with the mobile-bearing knee at 5 to 8 years. A randomized controlled trial presented at this year’s American Academy of Orthopaedic Surgeons Annual Meeting by David W. Murray, MD, revealed no difference in functional outcomes or reoperation rates between mobile-bearing and fixed-bearing designs among more than 500 patients at 5 years. In a meta-analysis by Wen and colleagues published ahead of print in Archives of Orthopaedic and Trauma Surgery, 15 studies that included 1,950 knees revealed no statistically significant difference between mobile-bearing and fixed-bearing knees in KSS, patient preference and complications.
Pinczewski has studied components made with oxidized zirconium. Although this material has shown 10 times better wear than cobalt chrome with polyethylene in the laboratory, this material has demonstrated no clinical differences compared with standard implants at 2- and 5-years of follow-up.
“But that doesn’t mean that there isn’t going to be a difference with more time,” he said. “In the younger patients, in whom we tend to use the premium implants, we have to use the best possible thing we can use. … The reason we use this [material] is because of its potential to last longer.”
Direct-to-consumer marketing has played a part in the use of premium implants, according to Greenwald.
“You have to recognize the fact that if you can produce a premium implant and sell it as such, you can charge a premium price for it,” he said.
With surgeons, patients and hospitals contributing to the decision of which implant to use, “the key would be to make a somewhat premium knee at a reasonable price,” Kelly said.
To answer the question of whether premium implants will demonstrate justification for their additional costs, Gioe and others are calling for more registry studies from larger registries in Europe and Scandinavian countries, and from the developing U.S. national joint registry, the American Joint Replacement Registry, for which Gioe serves on the board of directors.
“With that kind of power, you can really sort out differences between designs as far as implant survival is concerned, where you can pick up a potential flaw in an implant,” Gioe said.
Greenwald said that ideally, the registry studies must have a 20-year follow-up.
“Twenty years is reasonable because if you look at standard implants, both in the hip and knee, you’ll find out that is not an unreasonable time frame to assess the durability of these systems,” he said. “There are many studies that suggest that and go out that far, certainly with standard implants.”
However, Pinczewski said that for information on functional results, more randomized controlled trials, longitudinal studies or cohort groups are needed. In addition, to shorten the time needed for the registry studies to evaluate survival, Gioe said some advocate radiostereometric studies, where “you can look at whether implants move, shift, subside or fail in a relatively short period of time — within a couple of years of implanting them — by doing special radiographic studies.”
Lombardi said that the extra cost for these implants is necessary to advance technology.
“We are all about advancing the technology, and in order to do that, we unfortunately have to design new things, come up with better materials and try to improve overall the results we are getting,” he said.
In addition, what might be considered a premium component now may be a standard implant in 10 years.
“If you go back say 20 years, a premium implant was an uncemented implant [or] the all-polyethylene tibial component. Twenty years ago, a titanium tray to support the polyethylene was considered to be premium,” Pinczewski said. “Well, you go back 10 years, the standard implants have titanium trays, and many implants are now uncemented.”
Innovation in TJA
Moving forward, Gioe said, the next few years will see developments that are “more evolutionary rather than revolutionary as far as design is concerned.”
He said increasing emphasis has been placed on how implants are inserted surgically, how surgeons perform their portion of the operation and how to do it better, and whether it can be done more reliably, for example with computer navigation or robotics.
“Of course, those things also add cost to the operation and a learning curve. As far as design iterations are concerned, I think some of the recent issues with metal-on-metal joints and the hypersensitivity reactions … have put a bit of a damper on the search for the next great bearing surface,” Gioe said.
Lombardi said he did not take the take-home message from Gioe’s short-term study of longevity to heart.
“I see deficits in what we have in our surgical armamentarium currently, and to me, it would be stifling to say, ‘Everything we have is great; we shouldn’t go out there and make anything new,’” he said. “The first thing that people talk about when there is a new technology is, ‘what is the cost?’ And not, what is the science behind it, what is the rationale, and what’s the expected outcome?”
Gioe emphasized that his study was not designed to deter or discourage innovation.
“I think all of us would be willing as patients, physicians and health care systems to pay for higher-priced implants if it was clear that higher-priced implants were achieving the goals that we want — improving function in patients, decreasing pain and improving longevity of the implant,” he said.
In addition, he stressed that a number of implants fail in the first few years for reasons unrelated to design, including infection and instability, which have more to do with patient biology or surgical technique.
“You have to separate the hype from the reality,” Greenwald said. “And the reality, unfortunately, does take in vivo time.” – by Tina DiMarcantonio