The earliest concepts for knee replacement appeared in the early 1860s when Themistocles Gluck, a German surgeon, first surgically implanted a hinge joint made of iron. It wasn’t until 1951 that Swedish surgeon Börje Walldius introduced the Walldius hinge joint. It was originally made of acrylic, evolving into a more durable cobalt chrome alloy version in 1958. These first hinge implants required removing the collateral and cruciate ligaments and provided limited movement. They also had a tendency to loosen, leading to early implant failure.
The Road To Modern Knee Implants
More modern knee replacement began in the United States in the early 1970s. The concept of resurfacing the tibio-femoral condylar surfaces with cemented metal surfaces, along with preservation of the collateral and cruciate ligaments, was developed and refined. To correct severe knee deformities, the condylar knee with posterior cruciate-sacrificing design was introduced, also in the early 1970s. By 1974, replacing the patellofemoral joint and either preserving or sacrificing the cruciate ligaments had become standard practice. Subsequently, condylar knee designs were improved to include modularity and uncemented fixation, combined with more precise instrumentation to allow easily reproducible alignment.
The late 1990s saw the introduction of a new facet of knee implant production: the medial pivot from Wright Medical. These pivots were developed in an attempt to better recreate how a natural knee moves. This is accomplished by creating a relatively stable medial compartment through the extension and flexion movements on the knee. A little before its time, the design was sold to a smaller company and fell off the radar and the patent expired. Recently this concept has resurfaced, in an effort to combat the mid-flexion instability associated with more traditional bearings. With the backing and further development by a major U.S. company (Zimmer-Biomet), what is now termed a medial congruent bearing is rapidly rising in popularity. Experts believe that within the next 8 years knee arthroplasties will increase to more than 3 million per year. The vast majority of these arthroplasties will involve implants using medial congruent knee bearings.
What Is So Special About Medial Congruent Bearings?
Studying the natural movement of the knee, known as knee kinematics, is critical to improving the overall performance of these implants. In the 1970s changes were made to ensure that the ligaments used in the knee’s normal function were not impinged or removed when an implant was inserted. This has led to fewer cases of kinematic conflict when the knee loses flexion or becomes impinged by the implant.
Limiting conflicts like these was the driving force in conceptualizing the medial pivot, or medial congruent bearing.
- The medial compartment of these implants serves as a ball and socket-style pivot point, aiding in smooth movement of the knee.
- The lateral compartment is shaped in such a way as to permit natural posterior roll during flexion.
- An anterior lip in the polyethylene bearing was added, preventing the tibia from moving further toward the back of the body than it would naturally.
A study of patients over 10 years revealed that this style of knee implant had excellent durability and reliability. Of the 58 patients studied, 98.6% experienced no failure or reduction in the effectiveness of the implant. Notably, this study was done on patients of Japanese descent who participated in their home culture, which involved significant deep flexion activities such as sitting on the ground and kneeling. Even with the increased demand, this lifestyle puts on implants, the results show that these implants can provide improved quality of life and mobility for decades.
Contact Your Specialist For More Information
These implants are an essential option that joint specialists offer to patients seeking improved function of a failing knee. As technology has advanced in the past decades, it’s become more accessible for patients to experience lasting benefits from implants like these. If you want to learn if medial congruent knee implants are an option for you, schedule an appointment with your joint specialist. They’ll provide you with a consultation, including a physical exam, to assess whether it is time for you to have a knee replacement. Call today and take the first step towards reduced pain and increased mobility with knee replacement!
Sources:
- Ranawat CR: History of total knee replacement. J South Orthop Assoc. 11(4):218-26, 2002.
- Miyazaki Y et al. Analysis of the kinematics of total knee prostheses with a medial pivot design. J Arthroplasty. 2011; 26(7):1038-1044.
- Ueyama H, Kanemoto N, Minoda Y, et al: Long-term clinical outcomes of medial pivot total knee arthroplasty for Asian patients: A mean 10-year follow-up study. J Knee. Dec;27(6):1778-1786, 2020
