In the first joint replacement surgery in 1890, the German surgeon Themistocles Gluck implanted “carved and machined pieces of ivory” into joints diseased by tuberculosis — starting with a knee replacement for a 17-year-old girl, according to the medical historian and author Dr. David Schneider. 

The implants used today, as well as those doing the implanting, are radically different from those in the days of Themistocles Gluck. 

In thousands of such procedures, robots are now assisting surgeons to ensure an optimum fit of the new joint. Although many doctors still perform the procedures successfully without their assistance, the robots’ ability to help achieve more precise implant positioning — often determined through 3-D computerised modelling of the patient’s joint before the actual procedure — makes their role likely to grow over the next decade as the implants become more individualised, and such technologies as augmented reality are integrated into the operating room. 

And the replacements themselves have changed. Over the past century, they have evolved to include metal, plastic and ceramics, and are now made of titanium, cobalt chrome and specially reinforced plastics. (Gone are the metal-on-metal replacements that caused problems in hip replacements in the past). 

But something else important has also changed: the psychology of the patients, specifically, baby boomers. Now in their late 50s, 60s and 70s, they represent about half of the patients for the most common, knee and hip replacements. 

“This is the first generation that is trying to stay active on an aging frame,” said Dr. Nicholas DiNubile, an orthopaedic surgeon in Havertown, Pa. “My parents weren’t active at all. If they went out and did something and were sore afterwards, they’d never do it again. But baby boomers stay active, in droves.” Dr. DiNubile, 67, author of several books on the subject, coined the term “boomeritis” to describe the wave of sports-related injuries he has been seeing in his practice among his cohort. “I’m still trying to play tennis at a high level,” he said. “My knees hurt sometimes, but I’m not stopping.” 

This change in attitude is a striking difference in the patient population, and some say it has helped drive the advances in orthopaedic surgery. “When I started practice 30 years ago, if someone had hip pain, we’d take an X-ray and even if they had arthritis, and were in their 40s, we’d tell them to modify their activity and wait,” said Dr. William Maloney, professor of orthopaedic surgery at Stanford University. 

No longer. “The technology caught up with our patients’ desire to stay active,” he said. 

One of the biggest innovations came in the late 1990s and early 2000s — just in time for the marathon-running, tennis-playing boomers to start showing signs of wear and tear. “The industry figured out a way to make the implants better,” said Robert Cohen, president of digital, robotics and enabling technologies for Stryker’s Orthopaedic joint replacement division in Mahwah, N.J. “We used the exact same plastic — relatively soft, but durable — and put it through a post process, of heat and radiation, that made it even stronger.” The “highly cross-linked polyethylene” implants significantly reduced the need for revision surgery. “One of the main reasons for revision was the polyethylene breaking down in the replacement joint,” he said. Thanks to the advent of the stronger, more durable material, he says, “we’ve pretty much eliminated that.” The new implants also helped lead to faster recovery times. Dr. Matthew Sloan at the University of Pennsylvania, the lead author of the 2018 study, said that “among the older patients, the big driver is the desire to stay active.”