The evidence and the alternatives to TKA in patients younger than age 65

Mary Ann Porucznik

Over the last two decades, the volume of total knee arthroplasty (TKA) procedures has increased dramatically—and the percentage of TKA patients who are younger than age 65 has also risen substantially. During a joint Specialty Day program moderated by Carlos J. Lavernia, MD, members of The Knee Society and the American Association of Hip and Knee Surgeons examined the changing demographics, historic outcomes, failure modes, different approaches, and bearing surfaces available to TKA patients.

Changing demographics
According to Kevin J. Bozic, MD, MBA, not only are TKA patients getting younger, their expectations are getting higher. “In 1999, about 30 percent of TKA patients were younger than age 65,” said Dr. Bozic. “In 2008, patients younger than age 65 accounted for 41 percent of all TKAs. And, as our patients get younger, they expect that they will be able to do more with a TKA.”

He pointed to a recent systematic review that found TKA in younger patients was justified, even though registry studies “clearly show a higher rate of failure and earlier revisions in younger patients, which is what we would expect.” As the number of TKAs has increased, he noted, the number of high tibial osteotomies (HTO) has declined. “So what is the future management of the young arthritic knee?” he asked.

In his view, the emphasis will be on prevention, and the shift will be supported by changes in the reimbursement system, which will provide incentives for managing the health of a population, rather than for performing procedures. He reviewed a variety of nonsurgical treatment regimens being developed, including experimental drugs, nutritional supplements, injections, and biologic treatments for early-stage arthritis. “I think this is the area where we will see the most innovation over the next decade,” he said.

“Finally,” he concluded, “we have to have better implants and surgical techniques. Robotic surgery could improve the reproducibility of our operations and allow these operations to be performed more safely in younger patients—and that will lead to better long-term outcomes.”

Historic outcomes
In reviewing TKA outcomes in patients with more than 30 years of life expectancy, Richard D. Scott, MD, started with a question: “Did you know that the United States ranks 36th among nations in terms of life expectancy, with an overall life expectancy of 78.3 years? Do you know who’s number 1? It’s Japan—at 82.6 years.” For this reason, “we have to look at people who receive the TKA in their fourth or fifth decade of life,” said Dr. Scott.

But in examining his own practice, he found something surprising—the average age of his TKA patients had not changed dramatically during the past 20 years. “In 1990, the average age of my TKA patients was 67.4 years; in 2000, it was 67.2 years, and in 2011, it was just about 68 years of age,” he reported.

“So, what was going on? Well, when I graphed my patient population by age distribution, I found that in 1990, I had a bell-shaped curve with a very narrow margin. By 2010, I have the same average, but the standard deviation is getting much bigger. So at least for me, I’m doing more older people—in their 80s or 90s—as well as a lot more younger people,” said Dr. Scott.

According to Dr. Scott, several conditions might lead to TKA in patients younger than age 65, including the following: rheumatoid arthritis (RA), skeletal dysplasia, posttraumatic arthritis, infections, ligament injury reconstruction, and meniscectomy. Based on the literature, he noted, younger TKA patients have a return to surgery rate of approximately 1 percent per year, although most studies have had relatively short (less than 10-year) follow-up. Among patients with RA, who have a relatively low activity rate, studies have shown up to 100 percent implant survivorship at 15 years.

Unicompartmental knee arthroplasty (UKA) in this age group, noted Dr. Scott, has several advantages, including preservation of bone stock, more normal kinematics, and a higher level of performance. UKAs, however, also have a higher revision rate, based on registry studies.

“This generation that we’re operating on now, they want high function and perfect results—and they want them now,” said Dr. Scott. “I recently heard from a 47-year-old patient who is a competitive tennis player. She wrote: ‘Staying active with tennis, swimming, and the occasional 2-mile run; I hope my knee isn’t being too taxed!’”

Failure modes
Based on an analysis of systematic reviews, Timothy M. Wright, PhD, reported that TKA failure mechanisms in younger patients are primarily mechanically related. “They include patellofemoral problems, component failure, wear, osteolysis, and loosening,” he said. “So the mechanical burden placed on the knees in younger patients must be greater than that in older patients. But how much greater is the burden in these young patients? Unfortunately, we simply don’t know.”

Dr. Wright described groundbreaking work conducted by Clifford Colwell, MD, and Daryl D’Lima, MD, PhD, to measure direct in vivo contact forces in relatively older patients (age 70 and older). “As these patients became more active, loads went up,” said Dr. Wright. For example, jogging at about 5 mph results in a tibiofemoral joint force greater than 4 times body weight; swinging a golf club or a tennis racket generated similar loads.

“But we can’t accurately predict what those forces will be in younger patients,” continued Dr. Wright. “We certainly expect them to be higher, because these patients are more active, but how much higher is anyone’s guess. And the same is true for patellofemoral forces; we really can’t predict them. We need to understand the duty cycle placed on these implants and develop computational models to get an idea of the true mechanical burden and the impact of patient weight.”

The good news, he noted, is that even though the mechanical burden is higher, the bone quality—particularly in the cancellous bone—is better. “We’re going to need to know more about both the quality of bone and the applied load in younger patients to make predictions about failure,” said Dr. Wright. “We need that information—an understanding of the mechanical burden on the knee—to develop better devices and better materials.”

Doing something different
“Optimizing nonsurgical treatment is important for younger patients. Unfortunately, in my own practice, we see patients who had minimal radiographic evidence of arthritis and may have had inadequate nonsurgical treatment and are now unhappy after their TKA,” reported Craig J. Della Valle, MD. “That being said, there is a point—even in a very young patient—where you can wait too long. Once range of motion is limited and patients begin to experience flexion contractures, TKA results aren’t going to be as good.”

Dr. Della Valle recommended extensive patient education for younger TKA patients, focused on the risks, benefits, and realistic expectations. He stressed the need for regular follow-up with these patients, encouraging them to report any problems so that they can be addressed early.

“I also think some patients should consider alternatives to TKA, such as high tibial osteotomies, particularly if they want to engage in running sports,” he said, noting that he refers patients to a colleague with experience in performing osteotomies to give them a realistic idea of the pros and cons of that procedure.

“Unicompartmental knee arthroplasty is also something to consider in this patient population,” he continued. “A ‘uni’ preserves both cruciate ligaments, doesn’t alter the patellofemoral articulation, leaves the rest of the knee intact, and may be associated with higher satisfaction in the more active patient. Studies presented during the AAOS Annual Meeting found good results among patients younger than age 55.”

Because the literature on outcomes associated with cementless fixation has been mixed, he advised caution for this form of TKA. “Creating a biologic bond between the implant and the patient makes a lot of sense,” he said, “but we need to move carefully with our younger patients, and cemented fixation is still probably associated with the most reliable outcomes.”

Another option is the use of a nonmodular tibial component (either all-polyethylene or metal-backed). But literature reports have been mixed and outcomes may be design-specific or more dependent on the quality of the polyethylene used rather than the modularity. Other areas that lack supportive data include the use of cruciate-retaining as opposed to posterior-stabilizing designs and fixed bearings as opposed to rotating platform designs. “Although some surgeons really believe in these different approaches, the data thus far do not suggest true superiority of one over the other,” said Dr. Della Valle.

Although new and often unproven technology may be used with younger patients, in retrospect, many of these technologies have been found to provide no benefit or to be associated with inferior results. To avoid early failures, “I think the best idea may be to stick to what you as a surgeon do well,” he concluded.

Bearing couples
According to Michael D. Ries, MD, polyethylene wear has historically been the primary cause of TKA failure, and the durability of the bearing couple may determine how long a TKA lasts in a younger patient. He reviewed the development of cross-linked polyethylene bearings, particularly in the hip, then turned to the situation in the knee.

“The counterface can also contribute to wear,” he said. “The femoral component is cast cobalt chrome, which can scratch in vivo. If that happens, the metal surface may deform, creating a ridge. The additional metal above the substrate level can cause wear.” As a result, researchers are seeking ways to make the surface harder and more scratch-resistant.

“Oxidizing zirconium is one method,” said Dr. Ries, “where the substrate is a zirconium metal, similar to titanium, and the surface is transformed into a ceramic to make it more scratch-resistant.” However, radiographic wear is difficult to measure in knees, and early-to-midterm clinical studies have not found a significant difference in outcomes between cobalt-chrome and oxidized zirconium bearings.

“Ultimately, we need retrieval studies of these materials to help better determine the risk of in vivo oxidation in newer highly crosslinked polyethylenes and the effect of counterface hardening on wear” concluded Dr. Ries.

Disclosures: Dr. Bozic—Agency for Healthcare Research and Quality (AHRQ); AAHKS; American Joint Replacement Registry; American Orthopaedic Association; California Joint Replacement Registry Project; California Orthopaedic Association; Orthopaedic Research and Education Foundation; Dr. Scott— DePuy, A Johnson & Johnson Company; Conformis; Dr. Wright— Mathys Ltd; Exactech, Inc.; Synthes; Stryker; Journal of Orthopaedic Research; Wolters Kluwer Health/Lippincott Williams & Wilkins; Dr. Della Valle— Biomet; Convatec; Smith & Nephew; CD Diagnostics; Stryker; Journal of Bone and Joint Surgery–American; SLACK Incorporated; Orthopedics Today; AAHKS; Arthritis Foundation; Knee Society; Dr. Ries—Smith & Nephew; Stryker;. OrthAlign; The Knee; Foundation for the Advancement of Research in Medicine.

Mary Ann Porucznik is managing editor of AAOS Now. She can be reached at porucznik@aaos.org .

Bottom Line

• As the number of younger patients with arthritic knees increases, the emphasis will shift to prevention, and improvements in surgical techniques and implants will lead to better long-term outcomes when TKA is performed.
• The most common mechanisms of failure in younger TKA patients are mechanical, due to the higher applied load in these patients.
• Optimizing nonsurgical treatment is important for younger patients; alternatives to TKA include high tibial osteotomies and unicompartmental knee replacement.
• The durability of bearing surfaces may determine the longevity of a TKA; more research is needed to determine the impact of newer materials such as crosslinked polyethylene or oxidized zirconium.