The first knee replacement was performed in 1890 by Themistocles Gluck, a German surgeon who implanted an ivory hinged prosthesis into a patient’s knee and fixed it in place with a primitive cement made partly from pumice and plaster of Paris. That procedure was radical, experimental, and largely unsuccessful by modern standards, but it planted the idea that a destroyed knee joint could be replaced with an artificial one. The story of how that idea became one of the most common and successful surgeries in the world stretches across more than a century of trial, failure, and incremental reinvention.
Gluck’s Ivory Knee and the Birth of Joint Replacement
Themistocles Gluck was working in Berlin in the late nineteenth century when he began experimenting with replacing damaged joints using carved ivory components. By 1890 he had designed a hinged ivory knee joint and implanted it in a patient, securing it to the bone with a fixative compound he developed himself. The concept was visionary for its time: Gluck also experimented with ivory replacements for the hip, elbow, and wrist, making him arguably the first surgeon to attempt what we now call total joint replacement.
The results, however, were poor. Infection was rampant in an era before antibiotics, and the body did not tolerate the ivory implants well over time. Gluck’s work was met with heavy criticism from his contemporaries, and the idea of replacing an entire joint with artificial materials was largely abandoned for decades. It would take more than half a century before surgeons circled back to the concept with new materials and better surgical technique.
The Hinge Era of the 1950s and 1960s
Modern efforts to replace the knee joint began in earnest during the 1950s and 1960s, when surgeons developed metallic hinge-type implants designed to address severe arthritis and ligamentous instability. These devices worked on a simple mechanical principle: a metal hinge bolted to the femur and tibia, allowing the leg to bend and straighten but restricting virtually all other movement. The knee, though, is not a simple hinge. It rotates slightly, glides, and shifts as it bends. Locking it into one plane of motion created problems.
One of the better-known hinge designs was the Walldius prosthesis, developed by the Swedish orthopedic surgeon Borje Walldius. A study reevaluating 45 Walldius knee joints about three years after implantation found that roughly three-quarters of patients had good to excellent outcomes compared to their preoperative condition. But the complication rate was high: infection accounted for about 11% of failures, and the overall success of the surgery depended heavily on the health of adjacent joints, which frequently limited how much a patient’s walking ability actually improved even when the implant itself worked well. The authors emphasized that cement fixation was critical to prevent the prosthesis from migrating or fracturing the bone shafts.
These hinge implants were a meaningful step forward for patients with severely destroyed knees who had no other options, but the approach had fundamental limitations. By constraining all movement to flexion and extension, the hinge transferred unnatural stresses to the bone-implant interface, leading to loosening over time. And the amount of bone that had to be removed to install them, sometimes around three centimeters, made salvage surgery difficult if the implant failed. The field needed a design that respected the knee’s actual biomechanics rather than replacing them with a mechanical approximation.
Frank Gunston and the Polycentric Knee
The pivotal shift came in 1971 when Canadian orthopedic surgeon Frank Gunston designed and implanted the first prosthesis that attempted to replicate natural knee biomechanics rather than simply acting as a hinge. Gunston’s polycentric knee arthroplasty used separate metallic runners attached to the femur that articulated against polyethylene tracks cemented to the tibia. Instead of forcing the knee into a single axis of rotation, this design allowed the two sides of the joint to move somewhat independently, mimicking the way a real knee has two distinct contact points that shift during bending.
Gunston’s design was not perfect. The small components sometimes loosened, and the fixation was not always durable. But the conceptual leap was enormous. For the first time, a knee replacement was built around the idea that the prosthesis should work with the body’s natural movement patterns rather than imposing an artificial one. Every modern knee replacement traces its lineage back to this principle.
The Total Condylar Prosthesis and the Modern Template
The design that brought knee replacement into the modern era was the total condylar knee prosthesis, developed at the Hospital for Special Surgery in New York during the mid-1970s. This implant evolved from experience with several earlier prosthetic designs and introduced a key innovation: patellar resurfacing, which addressed the kneecap’s role in the joint and reduced a common source of postoperative pain. The total condylar design replaced the entire bearing surface of the knee with metal and plastic components while preserving more of the surrounding soft tissue and ligaments than hinged designs required.
The five-year results established that this approach was far more reliable than anything that had come before. Pain relief was consistent, range of motion was improved, and the implants proved more durable than hinged alternatives. The total condylar prosthesis became the template on which virtually all subsequent knee replacement designs have been built, and its fundamental architecture, a metal femoral component, a plastic tibial bearing surface, and an optional patellar button, remains the standard today.
Why Knee Replacements Fail
Understanding why early designs failed, and why even modern implants sometimes do, helps explain the trajectory of knee replacement innovation. The reasons for failure have shifted considerably over the decades. Historically, the most common causes were aseptic loosening (the implant separating from the bone without infection), instability, and poor alignment during surgery.
A study of failures in patients aged 55 and younger found that the leading cause was polyethylene wear, accounting for about 44% of cases, followed by infection at roughly 39% and component loosening at about 12%. Polyethylene wear is particularly insidious: as the plastic bearing surface degrades, it sheds tiny particles that trigger an immune response in the surrounding bone, leading to bone loss (called osteolysis) and eventual loosening of the implant. This was a major driver of revision surgery for decades.
As polyethylene manufacturing improved, wear-related failures became less common, and the pattern of failure shifted. A modern review of the literature found that improvements in polyethylene production have made osteolysis from wear debris a less dominant mode of failure, with infection and instability now accounting for a larger share of revisions. In other words, the materials science caught up with many of the mechanical problems, leaving biological complications like infection as the more stubborn challenge.
The Polyethylene Revolution
The plastic bearing surface in a knee replacement takes an extraordinary beating. Every step you take compresses it between two metal surfaces, and over years that adds up to millions of loading cycles. The material used for this job in the vast majority of knee replacements is ultra-high molecular weight polyethylene, or UHMWPE, a remarkably tough plastic that was first used in joint replacements in the 1960s.
Early polyethylene formulations wore down faster than surgeons hoped, shedding the microscopic particles that caused osteolysis. Manufacturers responded by developing highly crosslinked versions of the material, which resist wear far better. But crosslinking created a new problem: the process generates unstable molecules called free radicals within the plastic, which can cause the material to degrade over time through oxidation. To address this, newer generations of polyethylene are treated with antioxidant compounds that stabilize those free radicals without sacrificing the mechanical strength gains from crosslinking.
The result is that today’s polyethylene inserts last considerably longer than those from even twenty years ago. Modern UHMWPE modifications combine crosslinking, thermal treatments, specialized sterilization techniques, and biocompatible stabilizers in various combinations, all aimed at producing a bearing surface that resists both mechanical wear and chemical degradation. Each manufacturer’s formula is slightly different, and the research comparing them is ongoing, but the overall direction is clear: wear-related failure is becoming less and less common.
Cemented Versus Cementless Fixation
One of the most consequential decisions in knee replacement is how the implant is attached to the bone. For most of the procedure’s history, the answer has been bone cement, a fast-setting acrylic compound that fills the gap between the metal implant and the bone surface and locks everything in place immediately. Cement fixation has an excellent track record and remains the most common method worldwide.
Cementless fixation takes a different approach. Instead of using cement, the implant surface is coated with a porous or textured material, often titanium or a specialized coating, that encourages bone to grow directly into the prosthesis over time. The idea is appealing: a biological bond rather than a chemical one, which could potentially last longer and be easier to revise if needed. Early cementless designs, however, had significant problems with aseptic loosening due to osteolysis and micromotion, meaning the implant would shift slightly before the bone could grow in, leading to pain and failure.
More recent designs have addressed many of those issues. A study of a current-generation cementless knee replacement using a highly porous titanium tibial baseplate found, at a minimum of ten years of follow-up, effective pain relief, high patient satisfaction, and survivorship of about 97%. Changes in implant design, including better surface textures and improved coatings, have helped with bone ingrowth and stability. Cementless fixation still occupies a smaller share of the market than cemented, but its use is growing, particularly in younger, more active patients whose implants need to last several decades.
Partial Knee Replacement
Not every arthritic knee needs a full replacement. The knee has three compartments, and when only one is damaged, replacing just that section can preserve healthy bone and ligaments while providing pain relief. This concept, called unicompartmental knee replacement, has its own parallel history.
The procedure has evolved considerably over the past several decades, and there is growing demand for it as a treatment for degenerative osteoarthritis or osteonecrosis affecting a single compartment. Modern unicompartmental surgery is often performed through a smaller incision than total knee replacement, preserving more of the joint’s native anatomy and generally offering a faster recovery. Patients who are good candidates often report that the knee feels more natural than a total replacement because the cruciate ligaments and the two healthy compartments are left intact.
The catch is patient selection. Unicompartmental replacement works well when the disease is truly limited to one compartment and the ligaments are intact. In patients with more widespread arthritis, inflammatory conditions, or significant ligament damage, a total replacement remains the better option. The revival of interest in partial replacements reflects a broader trend in orthopedics toward less invasive procedures and more personalized surgical planning, but it also comes with higher revision rates than total knee replacement, primarily because disease can progress in the untreated compartments over time.
Computer Navigation and Robotic Assistance
One of the most significant recent developments in knee replacement is the use of computer-assisted surgery and robotics to improve the precision of implant positioning. Computer-assisted navigation was introduced as a tool to help surgeons achieve more accurate alignment and positioning of knee replacement components. These systems can be divided into passive systems, which provide real-time feedback and guidance while the surgeon performs the cuts manually, and semiactive or active robotic systems, which physically assist with or perform certain cutting steps.
The appeal is straightforward. Even experienced surgeons working freehand with conventional instruments produce a range of alignment outcomes, and malalignment is one of the established causes of implant failure. Computer navigation and robotic systems aim to tighten that range, ideally placing every implant within a narrow window of optimal alignment. Early evidence has been encouraging, though the technology adds cost and operative time, and the long-term data on whether navigation translates into measurably longer implant survival is still accumulating. The trend, particularly among high-volume joint replacement centers, is clearly toward greater adoption of these tools.
How Long Modern Implants Last
Durability has been the central engineering challenge of knee replacement from the very beginning. Gluck’s ivory hinge failed within months. The Walldius metal hinge represented an improvement but was plagued by loosening and infection. Each successive generation of design and materials has pushed longevity further.
Today, large national joint registries from countries that track every implant placed show that roughly 90% of modern total knee replacements are still functioning well at 15 to 20 years. Some patients get 25 years or more from a single implant. That is a remarkable achievement for a mechanical device that gets loaded thousands of times a day inside a biologically active environment. The improvements in polyethylene, fixation methods, and surgical precision described in this article all contribute to that durability.
For younger patients, though, longevity remains a concern. A person who receives a knee replacement at age 55 has a reasonable chance of outliving their implant and needing a revision, which is a more complex procedure with somewhat less predictable outcomes. A study examining failures specifically in patients 55 and younger found that polyethylene wear and infection were the dominant causes, underscoring that a more active lifestyle places greater demands on the implant. This is one reason surgeons sometimes recommend delaying replacement as long as possible in younger patients, and why research into more durable materials and cementless fixation, which may be easier to revise, is particularly relevant for this group.
From Ivory to Titanium in 135 Years
The distance between Gluck’s 1890 ivory hinge and today’s computer-navigated, antioxidant-stabilized knee replacement is vast, but the underlying problem has remained the same: how to create an artificial surface that can bear enormous loads, move in complex ways, resist biological attack, and last for decades inside a living body. The solutions have come from an unlikely convergence of fields. Metallurgy contributed cobalt-chromium and titanium alloys. Polymer chemistry produced crosslinked and antioxidant-doped polyethylene. Biomechanical research, starting with Gunston’s polycentric concept, showed that the implant had to respect the knee’s natural movement rather than replace it with something simpler. And computer science, most recently, has provided tools to place these implants with a level of precision that the human hand alone cannot consistently achieve.
Roughly two million knee replacements are performed worldwide each year, making it one of the most common elective surgeries on the planet. Each one is a direct descendant of the moment in 1890 when Themistocles Gluck carved a hinge out of ivory and decided to see what would happen. The answer, eventually, was one of the great success stories of modern surgery, though it took the better part of a century and the collaboration of dozens of disciplines to get there.