The Great Debate: Mobile- vs. Fixed-Bearing Knees
Dr. Douglas Dennis and Dr. Alfred Tria debated the merits of these implants at ICJR’s Pan Pacific Orthopaedic Congress.
Mobile-bearing knee designs were introduced in the 1970s, and ever since then, orthopaedic surgeons have debated the question: Which is better for patients who need a total knee replacement, a mobile-bearing or a fixed-bearing implant?
The answer is unclear – and likely will not be clear for another 20 years or more, according to Douglas A. Dennis, MD, from Colorado Joint Replacement, Denver, Colorado.
At ICJR’s Pan Pacific Orthopaedic Congress, Dr. Dennis took the side of mobile-bearing knees in a debate with Alfred J. Tria, Jr., MD, from St. Peter’s University Hospital, Somerset, New Jersey, who argued in favor of fixed-bearing implants.
Mobile-bearing designs have been shown to allow conformity in the coronal and sagittal planes without increasing fixation stresses, Dr. Dennis said. This helps to decrease paradoxical sliding/shear, improve patellofemoral mechanics, and make the devices more tolerant of femoral condylar lift off.
Dr. Dennis acknowledged that the 10-year data show equivalent results between the two implant designs. But that is because the studies were done in older, lower-demand patients, he said.
Today’s TKA patients are younger, more active, and have a longer life expectancy, Dr. Dennis pointed out. It may take two decades, but he believes studies of mobile-bearing knees in this population will show the superiority of the mobile-bearing design.
Dr. Tria agreed that there are no differences between the two designs in terms of clinical results, range of motion, longevity of the implant, patient satisfaction, and wear rates.
What is different, thought, is the surgery itself: Surgery to implant a mobile-bearing knee is technically more demanding, Dr. Tria said, and it is performed less frequently than the surgery for a fixed-bearing knee. “What you do less often, you don’t do as well,” he remarked.
Registries do not favor the use of mobile-bearing knees either, he added. He cited data from the Australian and Swedish joint registries that showed higher revision rates for mobile-bearing than for fixed-bearing designs. And, Dr. Tria said, studies have shown that the contact points in a mobile-bearing knee are not kinematically correct.
He concluded that the use of mobile-bearing knees is a fascinating, enticing theory but with no better success than the use of fixed-bearing knees and plenty of room for failure.