The previous post describes Englishman John Charnley’s early efforts, mostly failures, to develop a total hip replacement. Although a patient’s squeaking artificial hip, which annoyed his wife, motivated Charnley to do better, finding the right material from which to make the cup component continued to elude him.
One day in 1962, not too long after Charnley recognized the shortcomings of PTFE (Teflon), a salesman stopped by Charnley’s hospital selling plastic gears, which came from Germany and were being introduced into machinery used in the weaving industry. He left a chunk of the little-known specialized plastic, polyethylene, an extremely hard and dense form, with the hospital’s supply officer, who passed it on to Charnley’s lab director. The investigator began immediately to test its wear properties even though Charnley’s initial response, after digging his thumb into it, was that the lab director was wasting his time. After 24/7 testing over three weeks, however, the material showed less wear than the PTFE had shown in one day. Charnley noted later, “We were on.”
Two other major hurdles still confronted Charnley. The first was how to solve the problem of securing the artificial components to bone such that the implants would not loosen and fail. Any glue would not stick to wet bone. Dentists, however, had successfully used acrylic cement to secure implants to jaw bones, and Charnley recognized its potential role in total hip arthroplasty. At the time of implantation, he mixed powder and liquid forms of the acrylic into a creamy paste and used it to fill any irregularities between the bone and the implant. Essentially grout rather than adhesive, the acrylic allowed for wide and even distribution of body weight forces between artificial hip components and the bones. It worked, and it is still used today. By the way, the same acrylic shows up in manufactured products under trade names such as Plexiglas and Lucite.
The other problem that hounded all investigators attempting total hip replacement was bacteria. Implanting these sizable metal and polyethelene components through large incisions greatly predisposed total hip replacement surgery to wound infections, far more so than most other operations. When the early hip replacements became infected, the only recourse was to tediously remove the components and chip out all of the cement. This left the patients no better off than if they merely had had the joint cut away in the first place.
Bacteria floating in the operating room’s air are inevitable, and some settle in the wound or on the surgical instruments, which then can transfer them into the wound. Charnley devised a three-pronged attack to minimize the exposure. He devised “space suits” to be worn by all of the operating room personnel. Each person thereby was completely isolated from the wound, which completely alleviated issues of bacterial contamination from loose hair, sneezing, or even breathing. Each space suit had its own ventilation system to keep the user comfortable. Then Charnley added highly efficient filters to the room’s ventilation system, which cleansed the air entering the room of nearly every bacterium and dust particle. Finally, the filtered air was channeled into a “laminar flow” pattern such that the cleanest air in the room was always in the vicinity of the surgical incision. Thereby any bacteria were zephered away from the incision and out of harm’s way.
By the late 1960’s, Charnley had worked out the problems just discussed, and total hip replacement became practical and safe. Orthopedic surgeons world-wide beat a path to his door to learn the procedure. Before they could return home with a set of Charnley’s instruments, he insisted that they take a 2½-day course and pass a test covering his methods—both for the operation itself but also for meticulous record keeping.
Today, the composition and shape of total hip implants continue to undergo refinement as do the surgical techniques for implantation. Over 300,000 total hips are implanted annually in the United States, and nearly one percent of Americans have one. With respect to improvements in quality of life, total hip arthroplasty compares favorably to the benefits bestowed by the treatment of high blood pressure with medication, chronic kidney failure by dialysis, and coronary artery disease by stents and bypass grafting.
Charnley was knighted in 1977 for his contributions. Other investigators have extended his pioneering work, and more recent advancements include development of similarly successful replacements for arthritic knees and shoulders. When individuals are otherwise healthy, a severely arthritic and painful large joint is debilitating. With every movement it reminds the owners of their frailty. Sir John’s contributions to modern medicine were monumental.