Scientific paper looks at long-term survival rates

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Peter Pollack

“There are pros and cons to different total knee designs,” said Robert T. Trousdale, MD. “Most of them offer good durability, but we wanted to compare long-term survival and outcomes for all-polyethylene tibial components against modular, metal-backed tibial components. Is there a difference in durability if the tibial component is a one-piece design?”

Dr. Trousdale is the corresponding author of Scientific Paper 228—All Polyethylene Tibials: A Survival and Infection Analysis Compared to Metal-backed Tibias—which was presented yesterday by Matthew T. Houdek, MD.

The research team reviewed data on 31,939 patients who had undergone primary total knee arthroplasty (TKA) between 1970 and 2013. Overall, 28,224 (88 percent) of patients received metal-backed tibial components, while 3,715 (12 percent) received all-polyethylene. Both cohorts had similar demographics with respect to gender, mean age, and mean body mass index (BMI). The mean follow-up was 7 years.

At 5-, 10-, 20-, and 30-year time points, the research team found that all-polyethylene tibial components were associated with significantly improved survivorship compared to metal-backed designs. In addition, all-polyethylene tibial components had significantly lower rates of infection, instability, tibial component loosening, and periprosthetic fracture.

“The infection rates we found were a little higher in the metal-backed designs than in the all-polyethylene designs,” explained Dr. Trousdale. “That was surprising to us, because most surgeons prefer to use modular total knees. I surmise that backside wear associated with modular designs may lead to irritation from polyethylene debris, leading to greater blood flow and an increased likelihood of seeding the knee with bacteria. But we haven’t investigated that directly.”

Overall, the all-polyethylene tibial components were linked to improved survival rates across all age groups, except in patients 85 years or older, among whom there was no significant difference. Similarly, all-polyethylene tibial components were associated with improved survival rates across all BMI strata, with the exception of morbidly obese patients (BMI ≥40 kg/m2), among whom there was no significant difference.

“The modular total knee appears to have a slightly increased chance of failure, but on the other hand, it may be a slightly easier revision,” explained Dr. Trousdale. “Most surgeons prefer to use modular total knees in young patients. I subscribe to the opposite philosophy; I use the design that’s likely to last the longest, which is the all-polyethylene component. Based on our research, my preference is to use all-polyethylene tibial designs for the majority of my patients, but there is an ongoing discussion in the orthopaedic world about which approach is best.

“Most current knee designs are new iterations of those reported on in our study,” Dr. Trousdale noted, “so these data may not apply to those presently in use. Over time, I think all of the designs have gotten better. The locking mechanisms of modular knee designs have been improved, which should increase the durability of the component. But based on long-term data among total knee designs available in the 1990s and early 2000s, monoblock, all-polyethylene tibias outperformed modular total knees. I recommend that surgeons use what they’re most comfortable with, bearing in mind the pros and cons of the various designs.”

Dr. Trousdale’s and Dr. Houdek’s coauthors are Eric R. Wagner, MD; Clint J. Wooten, MD; Cody C. Wyles, BS; Ryan J. Martin, MD; and Joseph R. Cass, MD.

Details of the authors’ disclosure as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure