SEVENTEEN
Implant Revolution
“The first industrial revolution used water and steam power to mechanize production. The second used electric power to create mass production. The third used electronics and information technology to automate production. Now a fourth industrial revolution is building on the third, the digital revolution that has been occurring since the middle of the last century. It is characterized by a fusion of technologies that is blurring the lines between the physical, digital, and biological spheres.”
—Klaus Schwab, founder of the World Economic Forum
And now, our own John Charnley has become part of surgical history, and has taken his place in the gallery of the great master surgeons who have gone before … the Charnley prosthesis is in essence a biological design by a man who was also an artist. It is something which a Leonardo da Vinci might have envisaged. But today we are thinking about the man, the human person we knew and held in affection. He had so much to give to the world of surgery, both in fundamental knowledge and to the relief of human suffering.”1
—Harry Platt
I’m performing shoulder surgery, but instead of wearing surgical scrubs, gown, cap, and mask, I’m sitting in my office chair in a white lab coat, dress shirt and tie. In fact, the patient is nowhere to be seen—only his scapula (shoulder blade) is here with me, a 3-D representation levitating on the computer screen in front of me. Just a few years ago, Stanley’s case would have been unmanageable by any shoulder surgeon in the world, so significant is his bone loss and deformity, but now his case has become almost routine.
I first met Stanley four months ago in clinic, a man at the end of his rope. He had undergone total shoulder arthroplasty eight years before in the Midwest, and while the initial results were excellent, over the last few years his shoulder slowly became more painful. I reviewed his original X-rays and told him I would have been pleased had the implant placement been my own; however, in the intervening years the metal and plastic parts had started loosening. At the time of implantation, orthopedic prosthetic parts have to be extremely stable and secure. Any slight wobble in the bone dooms the replacement to eventual failure, but even ideal time-zero positioning is no guarantee for success.
Sandy-haired with a ready, gap-toothed smile and smoker’s cough, Stanley had been evaluated by several surgeons prior to seeing me, and had been assured that his X-rays weren’t worrisome. After performing a physical examination and scrutinizing the new X-rays I told Stanley that I thought his total shoulder replacement was loose, and possibly infected, which caught him by surprise. As a sixty-one-year-old male, he confided that he needed to work for several more years before retirement, and the realization that his replacement had failed was distressing. I recommended that we operate, remove the loosened implants, test for infection, and assess the degree of bone loss. In these types of cases, an unsteady glenoid component (shoulder socket implant made of polyethylene, resembling white candle wax) inflicts slow-motion destruction to the socket-portion of the shoulder blade. As the cobalt-chrome metal head of the replaced humeral head revolves over the glenoid prosthesis, the pegs of the polymer component can start to unseat, working away from the host bone like a rickety wooden post wobbles and fails to support a garden gate. Ignored for too long, the bone of the scapula impalpably fades away, leaving an eggshell of bone encasing tapioca-like fibrous tissue and an unmoored polymer implant.
In my first operation with Stanley a month ago, I found what I had feared: massive bone loss, and implants that were swimming in sloppy bone. After opening the deepest part of his shoulder, I found a combination of metal, plastic, synovial fluid (resembling apple juice), and fibrous tissue. All the foreign implants had to be removed, and cultures of the tissue and fluid were obtained to ensure that no occult infection was present. I then placed a cement spacer, comprised of acrylic cement, representing a marriage of liquid monomers and a powdered polymer mix, similar to an epoxy project of my childhood, with the appearance of blue Play-Doh. This spacer, which replicates the shape and function of a regular shoulder bone, also contains powdered antibiotics, fighting deep infection while we awaited the culture results from surgery. With the cement spacer in place, we then do something miraculous: obtain a CT (computed tomography), a sophisticated 3-D series of X-rays that facilitates preoperative planning for the revision total shoulder replacement.
One week after surgery, we obtained a high-resolution CT of his shoulder. The computer is able to assimilate all the X-ray information with visual-imaging software and construct virtual 3-D images. In the last decade, the imaging software has become so good that surgeons and radiologists are able to “subtract” all the surrounding tissues away (muscles, ligaments, and tendons), and “build” the bony structures on the computer screen. Using computer key strokes, the physician can spin or rotate the images to get a sense of what the skeletal bones look like. Imagine your car mechanic not lifting the hood of your vehicle; instead conjuring what bedevils your engine with a magical tool that could see through metal. In the last few years, technology has allowed us not only to see the bones in three dimensions, but now to plan the surgery, virtually implant the parts, and assess the placement. Even more mind-boggling, I can now work with engineers to create custom shoulder replacement implants that fit the specific defects of a particular shoulder.
My conference call with the implant designer from Quebec is about to start. Using a link from an email message from the implant company Zimmer Biomet, I connect to a Webex teleconference with an engineer in Montreal. With a few keystrokes, I am able to navigate the layers of protection to keep Stanley’s information completely private. The engineer, Simone, speaks to me through my computer link, and she controls the images on the screen. On a light gray background, a 3-D image of Stanley’s scapula is presented. Simone controls the imaging software with her mouse, although I can ask for different perspectives and orientations of the shoulder blade. We work together, imaging and imagining; Montreal and Denver suddenly don’t seem very far away.
Simone cyber-manipulates the scapula, and it’s like having a Gray’s Anatomy drawing come to life and pirouette in front of me. Instead of a stout glenoid, with bony integrity to support a regular implant, I am staring at a pockmarked shoulder socket with a cavernous central defect, a pothole unable to support the metal baseplate I need to implant. Here, Simone now transitions to remarkable modernity: we will build an implant together that will be a computer-aided manufacture (CAM) metal that will perfectly fit in Stanley’s shoulder. His shoulder is so badly damaged that I would have never considered doing the case five years ago; today, I can work with Zimmer Biomet to custom-manufacture a one-of-a-kind implant that will fit hand-in-glove into the shell of bone, replete with the drill holes that will facilitate perfectly placed screws into the remaining bone. This system is a breakthrough that allows me to tackle a shoulder that five years ago I would have surrendered to. In less than an hour, we have completely designed the implant, and after signing off on the design, fabrication on the implant will begin in Warsaw, Indiana.
Weeks have passed since we designed the implant, and the day of surgery has arrived. Everything else about the case is routine, including the preoperative interactions, prepping, positioning, surgical approach, and dissection. But once I get down to the deepest part of his shoulder, the banality ends. The specialized implant is separately boxed in layers of sterile packaging, awaiting implantation. Its doppelgänger is a 3-D printed white polymer stand-in of the exact same dimensions, along with a 3-D printed version of Stanley’s shoulder blade. These life-size, lightweight, hard plastic models are identical to what I saw on the computer screen a few weeks ago, and help me to practice where I will place the real metal implant into Stanley’s ramshackle shoulder socket.
After cleaning the fibrous scar from the cavitary defect, I am peering deeply into the shoulder socket, an eggshell of bone instead of a fortification capable of supporting an implant. Formerly, I would have quaked at such a finding, but we are prepared. Instead of trepidation, I am filled with pluck, even bravado, because I am armed with a tool that can transform this case from disaster to triumph. I carefully position the trial polymer implant in the defect and it perfectly clicks into place. I spend a few moments examining the fit, and satisfied, insert the actual implant into the deep cavity. The heavy alloy, odd-shaped implant seemingly seats itself into the crater, like a spaceship pod docking into a spaceport, with no less science fiction conviction.
I secure the custom-milled implant to the scapula with multiple screws, whose trajectory and length I determined weeks ago. What was previously impossible now seems mundane. Carefully drilling through the metal implant and blindly drilling into the compromised bone, I already know the length of the screws. One by one, the screws are exactly the same length that was predicted weeks ago when I was a cyber-surgeon. After implanting all the screws, Stanley now hosts an implant that was planned in Montreal, expertly milled by a team of skilled technicians in Indiana, overnighted to my partner company representative Jodi, who ferried it to me today. Engineering, commerce, bioresearch, computer imaging, satellite and fiber optic communication, advanced manufacturing, airline shipping, cooperative sales engagement, skillful surgery, and exceptional anesthesia, nursing, and tech support have all fused together to care for this man with a terrible problem that today seems like not that big of a deal. Dr. Neer would be astonished, and duly proud.
Charlie Neer’s practice was similar to that of all orthopedic surgeons in the 1950s, when very few specialized in a particular joint. There were almost no specialty orthopedic clinics anywhere in the world, with the exception of hand surgery practices in San Francisco, New York, Chicago, and New York, under the guidance of the fathers of hand surgery, Sterling Bunnell and William Littler, among others. Dr. Neer continued to be a fracture doctor, even publishing a knee trauma paper in 1971, more than twenty years after finishing his residency. But as the pace of medical discovery quickened, surgeons like Charlie Neer trained their sights on particular joints. Just like the emergence of orthopedics as a specialty (separate from general surgery), the specialty domains of orthopedics were conceived by fanatics who were more narrowly obsessed.
War has always been a dastardly effective originator of advances in technology, transportation, communication, design, and medicine. With the advances in metallurgy and antibiotics during the 1940s, the orthopedic specialty was poised to launch into its most important era, but the treatment of arthritis had received little direct benefit. Charlie Neer had dedicated the first decade of his practice to fracture care, including surgical treatment of shoulder fractures.
For centuries, physicians and scientists have primarily communicated their discoveries to their colleagues via print journals. For academic university physicians, the credo of “publish or perish” mandated that a doctor actively conduct research and vie for journal acceptance. A young surgeon like Charlie Neer, imbued with optimism, energy, and a fresh set of eyes, was the perfect candidate to expose the inadequacy of orthopedics after the war. Dr. Neer’s classic 1953 article, “Fracture of the neck of the humerus with dislocation of the head fragment,” had highlighted the heretofore abysmal outcomes associated with nonoperatively and operatively treated severe fractures of the shoulder. On the last page of text in that article Dr. Neer included a photo of the shoulder implant he had designed, concluding, “replacement prosthesis presents logical possibilities and may prove of value in dealing with major injuries of the humeral head.”2 The world had its first peek at the future.
In 1955, Dr. Neer reported on a series of twelve patients who had undergone articular replacement of the humeral head.3 Using the implant he had designed, he was able to show dramatically improved outcomes when treating trauma patients. Implantation of the Neer prosthesis following trauma was a major step forward, but in this paper, Charlie Neer hinted at another indication. Of the twelve patients, all but one had suffered from a fracture-dislocation of the shoulder. A seventy-year-old housewife (patient number eleven) was treated for “hypertrophic osteoarthritis,” the world’s first partial (“hemi”) shoulder replacement for arthritis, on March 16, 1954. The patient returned to the Midwest, later writing Dr. Neer and telling him that she was “free of pain and leading a new life.” Instead of limiting the use of the shoulder implant to patients who had shattered their shoulder, Dr. Neer was offering the device for treatment of shoulder arthritis.
As the postwar boom led to unprecedented growth and prosperity, physicians were sanguine that disease could be challenged in ways never imagined. Antibiotics opened the door to entering the abdomen and operating on abdominal organs and the bowels. Mechanical ventilation during and after surgery bolstered surgeons’ ability to operate on ever-more critically ill patients. Pharmacological discoveries led to an explosion of medicines that made diseases like diabetes, malaria, gout, rheumatoid arthritis, and heart disease treatable. Finally, advances in chemistry and polymer sciences led to a handful of materials that are used millions of times every year in our world, including the world’s most common plastic, polyethylene.
Dr. Neer performed forty-six partial shoulder replacements in the first ten years, since his 1953 breakthrough. Of those forty-six hemi-arthroplasties, seven were for osteoarthritis and not for fracture. In his 1963 paper in the journal Surgical Clinics of North America, Charlie Neer concluded: “The results of prosthetic replacement have been better in this group than any other.” In the first decade, the father of shoulder surgery was performing less than one replacement per year for arthritis, but this number would quickly increase.
In Dr. Neer’s next major shoulder replacement publication, “Replacement arthroplasty for glenohumeral osteoarthritis,” a twenty-year report on shoulder replacement, the New York City surgeon reported on forty-eight patients who had undergone arthroplasty surgery for arthritis. Therefore, in the first decade of application, seven patients were operated on for arthritis, but 41 patients were treated in the second decade, an almost sixfold increase. In the 1974 article, Dr. Neer, once again, gave a sneak peek into the future. Buried in data table 1 is patient number eighteen, a fifty-seven-year-old housewife who underwent total shoulder arthroplasty, with placement of a polyethylene implant on the glenoid, or shoulder socket side. Dr. Neer explained, “The technique was modified in this patient by inserting a high-density polyethylene glenoid, anchoring it with acrylic cement and using a slightly different humeral element.”4
There is an illustration of the implant, but no X-ray. This “Neer II” Vitallium implant had been slightly modified by curving the edges and making the humeral head more spherical, and represents the primogenitor of all shoulder implants for the next several decades.
Every major orthopedic joint replacement developed since the 1960s has had three main characteristics in common: a plastic polyethylene cushion, a metal alloy articulating surface, and acrylic cement to hold the metal parts in place. Whether a shoulder, elbow, wrist, hip, knee, or ankle arthroplasty, every joint has been replaced with these three components. Newer developments have included cementless components where the texture of the implant causes bone ingrowth without the need for acrylic bone cement. This blueprint for joint replacement was drafted by Sir John Charnley.
Lancashire County lies in the northwest of England, and at one time was the world’s most important industrial and commercial center and the locus of international capitalism. Lancashire’s main centers are Liverpool and the world’s first industrialized city, Manchester. Although an ancient Roman fortification site, Manchester came to prominence following completion of canals and river improvements that facilitated transport of coal and processed cotton from the surrounding countryside and shipping to the River Mersey, Liverpool, and the world. The Industrial Revolution started circa 1780, and although cotton has never been grown in England, by the 1830s, Lancashire was responsible for almost all of the world’s cotton processing. The international influence exerted by Lancastrians would wane as the rest of the world emulated their steam engines, canals, factories, and trading centers, but arguably the most important Lancashire man of the last one hundred years came from the small town of Bury, outside Manchester.
John Charnley was born 1911 to a chemist father and nurse mother, and from a young age was noted to have a mechanical aptitude, building scale sailboats and tinkering with engines. John’s sister would attend Cambridge, but he would go straight to medical school in Manchester after matriculating from the Bury Grammar School, winning science prizes and achieving high grades. It seems that Charnley was destined for life as a surgeon, even sitting for the Royal College of Surgeons of England examination while still a medical student, which he easily passed.
Charnley graduated MB, ChB (Latin: Medicinae Baccalaureus, Baccalaureus Chirurgiae, equivalent to the American MD degree) as a twenty-four-year-old in 1935. He began a career as a surgeon, working in London and later, back in Manchester, under the guidance of the esteemed Henry Platt, one of the early English orthopedic pioneers. His future career plans were shattered with the outbreak of war on September 1, 1939, and he was enlisted in the Royal Army Medical Corps (RAMC) on May 1, 1940. At the same time German forces were sweeping across northern Europe (occupying Holland, Belgium, and France), Charnley was posted to Dover, across the English Channel from Dunkirk. He made multiple trips across the Channel to evacuate and care for the wounded, his life in grave danger during the miraculous evacuation of 370,000 troops from the French coast. He would later serve in the RAMC in Egypt and Palestine, all the while gaining invaluable experience in treating complex orthopedic injuries.
Once the war was over, Mr. Charnley (surgeons in England proudly retain the title of “Mr.”) returned to Manchester, working part time at the Royal Infirmary. Needing additional hospital work, Charnley accepted a position at the Wrightington Hospital, twenty-five miles north of Manchester. Why would the young surgeon accept a post at a remote hospital in the countryside? And why was the hospital built there to begin with?
Tuberculosis sanitarium facilities had been built around the world in the 19th and 20th centuries, following a typical pattern of rural, purpose-built, single-story hospitals (as recommended by Florence Nightingale), where open walkways, large windows, and fresh country air was thought to help patients combat TB. After Robert Koch had identified Mycobacterium tuberculosis in 1882, scientists could only dream of a magic drug to kill the bacteria. Until that breakthrough, the contradiction of prepossessing hospitals in pastoral settings, housing diseased, coughing victims dying slow-motion deaths would persist. The Lancashire County Council purchased Wrightington Hall from a financially distressed titled family in 1920, converting it into a nurses’ home with single-story hospital pavilions built to accommodate 226 chronic TB sufferers. Independent for decades, the hospital’s authority was transferred to the National Health Service in 1948, about the same time that Charnley began making monthly visits to the bucolic outpost.
Most of the patients at Wrightington were suffering from bone and joint infections, rotting from the inside, with only palliative solutions to consider. Interestingly, the incidence of TB began to decline just as Charnley began to consult at Wrightington. As sanitation standards improved (including milk pasteurization) and living conditions advanced, fewer children were contracting TB, and with the introduction of streptomycin and para-amino-salicylic acid in the 1940s, a TB cure was possible. “Sanatoria and orthopedic hospitals all over the country were faced with the same predicament—how to use effectively that large number of beds which had been available for tubercular patients, and which were now no longer needed.”5 Patients could rightly expect not to die from tuberculosis, but the ravages of the disease had not disappeared: the joints of the afflicted were still wrecked. As Themistocles Gluck painfully learned in 1890, replacing an actively infected joint was no solution at all. But now, Charnley could consider surgically confronting diseased joints, TB or not, with the inclination that one of mankind’s great burdens, arthritis, could be relieved, even cured.
While still working in Manchester (he still worked there part-time until 1958), Mr. Charnley evaluated a patient who had undergone a partial hip replacement with a Judet acrylic prosthesis (a clear plastic ball taking the place of the arthritic femoral head). The patient informed the sagacious surgeon that his replaced hip squeaked when he leaned forward. So severe was the screech that his wife could not tolerate his company. Instead of merely discounting the story (or even being amused by it), Charnley began to turn over in his mind why the noise was occurring. He observed that the sound rarely happened when the femoral head had been replaced following a femur fracture, where the cartilage from the hip socket was still intact (and ostensibly, still providing a slippery articulating surface), but these types of sounds only happened in arthritis cases where the hip socket had only roughened bone on both sides of the hip joint, squeaking when the replaced plastic ball interfaced with the arthritic hip socket. Importantly, instead of primarily focusing on implants and gadgets, Charnley turned his scrutiny toward the organic, considering the biomechanics (“the mechanical laws relating to the movement or structure of living organisms,” according to the Oxford English Dictionary) of the vital and diseased tissues he was pondering. His mentor, Sir Harry Platt, described Charnley as a surgeon-biologist, rather than a surgeon-engineer. To generate a solution for hip arthritis, he would first need to understand the function of healthy articular cartilage. This would become the pattern for every implant ever invented: comprehending function before proposing a cure. It now seems laughable that Gluck was implanting ivory implants in 1890, before antibiotics, sterilization, modern biomechanics, and the presence of metal alloys and polymers.
The Industrial Revolution brought machines and engines, with their crankshafts, pistons, gears, and axles—all of which required lubrication. Engine grease and distillated viscous fluids, newly discovered from the nascent petroleum industry, were used to lubricate the metal interfacing machine parts. If man is a machine, it was a reasonable conclusion that our parts had similar biomechanical relationships. Reasonable, but wrong. Charnley began discussing his theories with engineering friends at the University of Manchester, and they all agreed that our joints were not lubricated under the same principles as metal mechanical parts, which used hydrodynamic lubrication, where a very thin film of fluid separates the articulating surfaces and the parts move rapidly. Charnley and his colleagues theorized that our joints, instead, used boundary lubrication where the lubricant (synovial fluid) had an affinity for the joint surface itself. To test his hypothesis, John Charnley and the engineers started to build testing apparatuses to evaluate the “slipperiness” of cartilage.
The coefficient of friction (represented by the Greek letter mu, “µ”) is a mathematical ratio that expresses the friction between two surfaces. If the µ is very high, then a great deal of force is required to move an object against another. Rough sandpaper or a rubber tire has a µ value higher than 1. On the other hand, something very slippery, such as an ice skate sliding on ice, has a coefficient of friction of only 0.03, and it seems implausible that something could be more slippery than that. To determine the µ of cartilage, Charnley and his engineering cohorts built an apparatus that supported a platform, holding part of a human joint (a knee, and later, an ankle) in place. The upper half of the joint was positioned above, with a pendulum arm attached, which allowed the pioneering scientists to calculate just how slippery healthy cartilage is. What they discovered was astonishing. The coefficient of friction is 0.001, and is still the most slippery solid surface ever tested. It is (mathematically expressed) five hundred times more slippery than metal on bone and thirty times slicker than that ice skate on ice.
Mr. Charnley published his biological studies in non-surgical scientific publications; more important, he knew that the key to a good clinical outcome would be to design implants that had a low coefficient of friction. And he knew he could determine the µ with his testing apparatus while tinkering with the shape and size of the implants. The race was on to develop what he would always refer to as “low friction arthroplasty.”
Surgeons had been replacing arthritic and fractured femoral heads for over a decade, oftentimes with acceptable results, but Charnley was striving for better outcomes and longevity. To achieve true low friction arthroplasty, a “slippery substance” was needed for the socket, and he began querying the newly trained polymer scientists in England about possible candidates. He was eventually guided to polytetrafluorethylene (PTFE), also known as Teflon. When we hear the name Teflon, an egg skillet comes to mind, but its original use was industrial, in the manufacturing of valve seatings and non-lubricated bearings. Charnley evaluated Teflon, finding it to be biologically inert, creating almost no local foreign-body reaction once implanted in a human (he conducted no animal trials). Teflon is white, semi-translucent, almost waxy in appearance, and able to be cut with a knife. Starting in 1956, Charnley started performing the world’s first total hip arthroplasties, using Teflon cups that were pounded into the patient’s own bony hip socket. The results were amazing.6 Patients had wonderful range of motion and excellent pain relief. Charnley began reporting his results in the British Medical Journal and the Lancet, two of the most prestigious medical publications in the world.
One of the most dramatic changes Charnley made in hip replacement was the courage to change the size of the metal femoral head. All early hip pioneers, starting with Smith-Petersen and continuing with brothers Robert and Jean Judet and Austin Moore, had designed their partial joint replacements with a metal head that was the same size as the patient’s own femoral head. With the introduction of a synthetic hip cup, Charnley made a genius decision to decrease the size of the metallic head. Again focusing on low friction arthroplasty, he determined that a smaller head would provide less friction, and the head was therefore changed from Moore’s 42mm head (the size of a Ping-Pong ball) to 28mm, and finally to 22.25mm, about the size of an average toy marble. Many surgeons found John Charnley’s hip design laughable, but he had math on his side.
In the beginning, Charnley was implanting the Austin Moore hip stem with the large femoral head with no acrylic bone cement. After a few years of implanting the Moore prosthesis and Teflon cup, he was looking for a more stable method of implanting the femoral component. In older patients with weaker bone, the slender metal stem of the Moore prosthesis could begin to wobble in the canal of the femur, leading to subsidence and pain. Charnley was used to consulting with the scientists at the University of Manchester, and having had initial success with Teflon, he turned to some of the chemists in the department of prosthetics in the University of Manchester’s Dental School. Dentists were used to dealing with bony socket defects after the loss of a tooth; in England, following creation of the National Health Service in 1948, there were millions of patients who were seeking medical and dental treatment for the first time in their lives. This demand for healthcare led to a crusade to find better materials for dentures and tooth implants, and it was an organic chemist in Manchester, Dennis Smith, who recommended polymethylmethacrylate to John Charnley.
Polymethylmethacrylate (PMMA), also known as acrylic cement, is a self-curing cement that is formed by the simple combination of a liquid monomer and a powdered polymer. The watery liquid monomer is stored in a vial (with an inhibitor chemical), while the powder (with the appearance of powdered sugar) is saved in a pouch. At the time of surgery, the surgical assistant combines the two ingredients in a mixing bowl, akin to making bread dough. The mixture is initially creamy, then becomes doughy, and in a few minutes is like fresh Play-Doh. Polymerization is the frantic race of smaller chemical molecules, the “monomers,” linking with larger chain-like polymers to form a complex latticework of rigid matter. The chemical process is “exothermic,” meaning that heat is given off as the molecular linkage occurs, starting as a viscous slurry, then progressing to a pliable plastic, and as it hardens, an elastic blob, before becoming a solid piece of polymer. Today, we see PMMA every day, in Plexiglas windows, display cases, eyeglasses, signs, bathtubs, and skylights. But Charnley saw PMMA as the ideal grout for holding hip stems in place. Without experimenting on animals, he first started using it in humans in 1958, and was immediately convinced of its potential. A half century later, Charnley’s cement is used daily in every hospital in the world, with only slight chemical modifications.
Charnley left Manchester for good after 1958, initially working part-time in Wrightington, but eventually spending all his time at the previous TB hospital in the countryside. The local hospital board provided the funds for a biomechanical workshop and laboratory, and Charnley soon hired a laboratory technician, Harry Craven, a jack-of-all-trades who was at Charnley’s side for many years during the pivotal moments of the 1960s. The lab opened in 1961, and with a dedicated staff and purpose-built operating rooms, Charnley was optimistic enough in his ongoing success to give his epicenter a name, the Centre for Hip Surgery—Wrightington Hospital.
Like all innovators of science and medicine, John Charnley was a tinkerer. He made things, fixed machines, fabricated models, and fashioned his own implants. He also had a workshop in his own house, including a lathe where he turned his own hip socket implants from blocks of Teflon. Craven assisted him in these endeavors, and the task of making the widgets themselves was key to solving the problem of hip arthritis.
Flush with the excitement of a Hip Centre and hundreds of hip replacement operations under his belt, Charnley was hopeful that an acrylic-cemented hip implant with a small head and Teflon cup was the long-term solution to hip arthritis. He had gone from one hundred operations a year in 1959 to over four hundred hip replacements in 1962. Of course, as a scientist, Charnley was interested in following his patients and confirming their ongoing success. It was late in 1962 that Charnley realized that something horrible was happening. Despite the robustness of patients’ satisfaction and improved functional abilities, the three-year follow-up X-rays showed a disastrous change occurring in the Teflon cups. Charnley later explained:
It may seem strange that it took us some three hundred operations and between three and four years to arrive at this conclusion [that Teflon was unsuitable], but there were a number of different reasons. First, the results up to three years were so spectacular, and the patients so pitifully grateful, that we could not bring ourselves to face the suspicion that, in such highly successful results, the X-rays were showing incipient harmful evidence. Second, by its chemical nature PTFE [Teflon] was so extremely inert we felt that even if wear debris was present it would be harmless. Third, though we could see wear of the order of 1mm after about a year in the X-rays, I thought that this was not unexpected and could be explained by the “bedding-in” of the head in a socket that was deliberately machined to have an internal diameter larger than the head. It was only when the first year’s wear was more than doubled in the second year and more than tripled in three years that the seriousness of the problem became evident.7
On the precipice of a world-changing revolution, Charnley had to wonder if all was lost. All the X-rays showed a similar pattern of superior erosion of the “roof” of the Teflon cup, with the impression that the metal femoral head was working its way into the plastic cup like a hot knife through butter, albeit over the course of a few years. Mr. Charnley began to re-operate, and to his horror, realized that wear of the Teflon cup was not the chief problem. Worse, “wear debris” was found around the hip joints of patients who had suffered failure of the Teflon cups. He discovered globs of fibrous tissue surrounding the Teflon particles within the hip capsule. The adverse tissue reaction to a material he had initially concluded was “inert” reinforced the idea that Teflon, despite its early promise, was completely unsuitable for human use. To further confirm his hunch, Charnley prepared specimens of finely ground PTFE and injected them into his own thigh with a large bore needle. After waiting nine months, he dissected out the nodules underneath his skin, and examining the blobs of PTFE surrounded by an amalgam of fibrous tissue, knew that he would never use Teflon again. A block of Teflon in the body is inert; particles of Teflon are not. We are amazed that Charnley would inject Teflon particles into his thigh, but considering the action of his English forebear, John Hunter, the father of scientific surgery, who applied syphilitic pus onto a self-inflicted scratch on his own penis as an experiment, Charnley doesn’t seem as unhinged.
John Charnley, staring defeat in the face, was racked with guilt and was disconsolate. For weeks he lived in total despair, his wife (he had finally married at age forty-six) finding him awake at night, sitting up in bed with his head in his hands. She felt that “everything was gray and there was an all-pervading gloom.”8 The anguish lasted for weeks, when a chance discovery set him back on track.
In May, 1962, an industrial salesman representing a German plastics company arrived in Wrightington and asked to speak with Charnley, or his assistant John Craven. The salesman was selling plastic gear parts, which were being used in the Lancashire weaving trade (still substantial in the 1960s), and surmised that Charnley would need mechanical parts for his lab. Craven met with the salesman, and at a glance, saw the raw physical similarity to Teflon. He obtained a four-inch sample block of the material, high molecular weight polyethylene (HMWP), intent on showing Charnley.
Craven showed the block of polyethylene to Charnley, who handled it, dug his thumbnail into it, and realizing that he was able to score the material with his nail, concluded that the “poly” would be a similar disappointment as Teflon, and told Craven he was wasting his time. Undeterred, Craven kept the sample of the new polymer and planned on analyzing it in a custom-made testing apparatus he had devised. The initial results were astounding and incomparably better than Teflon had performed on the same Wrightington machine. Charnley left the country for a meeting in Copenhagen, and unknown to him, the machine churned on, oscillating the stainless steel heads over the HMWP block.
No doubt Charnley had left for Copenhagen empty of optimism, not even aware that HMWP was being tested in his lab. He had gained notoriety for hip arthroplasty, but as the horror show unfolded before him, Charnley had to wonder if he was a fool. When he returned from vacation, he later recalled:
My office door opened to reveal Craven who asked me to come down to the lab … Down I went to see the HMWP. After running day and night for three weeks, this new material, which very few people even in engineering circles had heard about at that time, had not worn as much as PTFE would have worn in twenty-four hours under the same conditions.
There was no doubt about it: we were on.
Charnley obtained more material from the German company, Ruhrchemie (later purchased by Hoechst AG), and like his previous experiment with Teflon, injected polyethylene into his thigh. After six months, there was no nodule formation in his leg. He wrote a letter, quickly published in the British journal Lancet on December 28, 1963, and reported his worrisome reaction to Teflon and encouraging response to the finely ground HMWP, partially motivated to warn surgeons about Teflon because he had heard surgeons were contemplating using it in a rudimentary knee replacement.
It only took a few months for Charnley to begin performing total hip replacements with polyethylene cups, starting in November 1962. Many of these early poly total hips were revision operations, taking out the failed Teflon cups and cementing in the new poly cups. Initially, all the cups were made by Charnley himself, and sterilized chemically by soaking them in Cidex (glutaraldehyde) overnight. Later, his manufacturing partner, Thackray, manufactured the cups and irradiated the poly with gamma irradiation (others recommended immersion in ethylene oxide—still controversial). He continued to implant the new HMWP cups by the hundreds, never using systemic antibiotics and only using stainless steel stems (and not cobalt chrome, like we use today). Charnley waited to publish his results, fearful of an unexpected Teflon disaster repeating itself, but it never happened.
In fact, John Charnley hardly changed a thing over the next twenty years, performing thousands of hip replacements in Wrightington (and later, in Midhurst as well), operating almost till the day he died, suffering a heart attack at age seventy. Even today, with more modern manufacturing processes, advances in metallurgy and polymer sciences, improvements in surgical techniques, and educational innovations, no one has ever demonstrated superior results compared to Charnley. The surgeon-biologist from a tiny town in rural England not only changed orthopedics, introducing materials that would be implanted millions of times every year in our world, but, as much as any person in the world, helped change the mindset that receiving a foreign substance into your body is extraordinary.
I should know: I am one of the millions of people who have had their hip replaced. And I’m extremely grateful to Sir John Charnley for immeasurably improving my life and relieving my previous suffering.
Charlie Neer first reported on the use of a polyethylene shoulder socket component in his 1974 article. His first use of the component was in 1973, and in a 1982 Journal of Bone and Joint Surgery article, Neer reported on 273 patients who had undergone total shoulder arthroplasty by him over a nine-year period.9 A decade of use of polyethylene in the hip had transpired before Neer attempted its use in the shoulder, in part because fixation in the shoulder was much trickier in the unforgiving, small shoulder socket. It boggles the mind that Charlie Neer was one of the few surgeons in the world performing shoulder replacement even three decades ago, especially in light of the fact that over 100,000 shoulders are replaced in America every year. This number pales in comparison to the half-million hip replacements and roughly one million knee replacements performed every year in the United States.
Joint replacement arthroplasty is the most commonly performed implant operation in the world. It is not only pain-relieving, it dramatically improves function and the ability to work and play. It is one of mankind’s greatest innovations, and the credit for discovering the combination of the right metals, plastics, and cement goes to John Charnley, an industrialist working with his own hands in an otherwise unremarkable countryside hospital.