Oxinium
Like most people, I had never heard of Oxinium. I vaguely remember the Table of Elements from high school chemistry. Near the middle of the chart is Zirconium, a chemical element with the symbol Zr and atomic number 40. Zirconium is a lustrous, gray-white metal that has no known biological role but due to significant advancements in technology, there is a new derivative material called Oxinium — Oxidized Zirconium — that is an extremely hard and highly scratch-resistant ceramic like material that has proven to be a superior metal for use in knee replacements. Not only can I spell oxinium now, I can walk on it — literally.
Although the knee joint may look like a simple joint, it is actually the largest and one of the most complex.The knee can be thought of like the hinge on a door, except that the knee not only bends back and forth but also has a complex rotational component that occurs as we flex and extend the knee. The knee is formed by the junction of three bones: the femur (the thigh bone), the tibia (the shin bone), and the patella (the kneecap). These bones are connected to each other by strong ligaments. Because of the location of the knee and the way we use it — or perhaps torture it — the knee joint is also more likely to be injured than is any other joint in the body. For those who are fortunate enough to avoid a serious injury they instead will likely wear it out.The combination of wear and tear, high longevity, and a desire for extended quality of life, are resulting in rapid growth of orthopedic surgeries to replace our knees.
The procedure of knee joint replacement is called a total knee arthroplasty (TKA). This surgery involves replacing your knee joint with a manmade one. In total knee replacement, each prosthesis is comprised of four parts. The tibia component has two elements and replaces the top of the shinbone (tibia). This prosthesis is made up of a metal tray attached directly to the bone and a plastic spacer that provides the load bearing surface. The femoral component then replaces the bottom of the thighbone (femur). The oxinium implant that rotates as we bend and flex our knee is said to be nearly 5,000 times more abrasion resistant than the cobalt chrome knees that had been used for many years. Projections are that the oxinium component will last 30-40 years. (Since I am 63, that should be enough!) The oxinium component on the end of the femur rests on a piece of plastic that replaces the worn cartilage — in my case completely worn out — that is made from Ultra high molecular weight polyethylene (UHMWPE). This special polyethylene has the highest impact strength of any thermoplastic made. The polyethylene surface is inserted onto the tibia component so that the weight is transferred metal to plastic not metal to metal. During the operation any deformities are corrected — I had my fair share of these — and the ligaments are balanced so that the knee is stable and has a good range of movement. The articular surface of the patella is removed and replaced by a polyethylene button cemented to the posterior surface of the patella. The new kneecap then slides smoothly on the front of the knee joint.
More than a half-million knee implant operations are carried out each year around the world, mostly for patients who are over the age of 65. The new materials, such as oxinium, are now making it possible to replace knees in people in their forties, and we will soon see millions of knees replaced per year. A British company called Smith & Nephew claims to be the leader in manufacturing of the components and the tools to install them. They are projecting revenue of nearly $4 billion for the year.
There are some pictures of what into my new joint in the photogallery. There is also a lot more to the story — both leading up to the need for a knee replacement and the process of having it done and the rehabilitation. Stories to follow.
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