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.
Zieglar prescribes continuous passive motion (CPM) because it enables patients to get back quickly-or never lose-good motion. “I use it for almost all of my outpatient shoulder surgeries, whenever I am going into the joint and it is not a labral repair or an instability case,” he says. Zieglar also uses CPM following distal clavicle excisions and acromioplasties, if a rotator cuff repair is not done. At the Center for Orthopaedics and Sports Medicine in Marietta, Ga, Rick Hammesfahr, MD, routinely prescribes CPM following total knee replacements, ligament reconstructions, and fractures, “procedures that are high risk for developing stiffness,”he says. CPM has also produced significant benefits following newer articular cartilage resurfacing procedures that result from isolated chip fractures on the ends of bone. “CPM not only helps prevent stiffness, but promotes nutrition of the articularcartilage that you are trying to heal,” he says. The benefits of CPM are recognized, although quantifying its value has been difficult. Its use early in recovery, Hammesfahr says, has a significant impact overall. “If you look at people who use CPM very early versus those who do not, there is a quicker, less costly rehab process.” Capitalizing on the 2 to 8 weeks immediately after surgery with passive stretching and movement before restrengthening muscle is significant, according to Zieglar. “Some patients are put in a sling for 4 to 6 weeks after rotator cuff repairs. Then you are fighting pain and stiffness and a weakened muscle after weeks of no motion.” CPM keeps the joint region stretched and warm, increasing blood flow and elasticity. “Patients get their motion back faster, they are off crutches sooner,” Hammesfahr says. They also find that it relaxes the area and provides pain relief. After setting up and training patients in the CPM machine before surgery, Zieglar begins them on CPM immediately post surgery, “that day, if they get home in time, or the next day for sure,” he says. Patients are recommended to spend 4 to 6 hours a day in the machine. Most divide up the therapy an hour at a time into hour-long segments. Additional increased motion and stretching exercises are demonstrated to patients during visits in the first and third weeks following surgery. With good motion after the first 3 weeks following the procedure, patients are well ahead in the healing curve when they begin physical therapy. “Up until that time, they should not be doing any active motion, just passive motion and stretching,” Zieglar says. “CPM gets the area jump-started in healing and ultimately we can avoid a lot of therapy.” In the past, managed care companies eyed CPM with cost-cutting scrutiny. The mistake, Hammesfahr says, was thinking money saved by eliminating CPM would outweigh money saved in the duration of physical therapy or additional surgeries if scar tissue developed. Attaining 110° to 120° of motion prior to physical therapy is usually the goal, he adds, and while many procedures have become more packaged, CPM’s use varies at his clinic. “It depends a lot on the procedure,” he says. Studies have also been unreliable in determining CPM’s impact on healing the joint. Most have looked at patients 1 or 2 years after surgery, another mistake according to these physicians. Accurate short-term studies require testing a singlesurgical procedure, as well as splitting patients into those who receive and those who do not receive CPM. Good patient pools are difficult to attain and the ethical issues are obvious, Zieglar says. “Most physicians can’t justify withholding therapy.” Studies have shown CPM’s value in pain reduction and its benefits after certain procedures. “Articular surface injury studies done 20 years ago showed that CPM therapy is beneficial for articular cartilage healing,” Hammesfahr says. The number and duration of prescribed medications are also reduced because tightness is lessened. Smaller, informal studies of the overall benefits of CPM have convinced Hammesfahr, as well as many insurance companies.
Letters of medical necessity, common 5 years ago, are much less common today. “I probably do one a year now. It is not a real issue anymore,” he says. While most HMOs have tightened coverage for both CPM and physical therapy following some procedures, preferred provider groups have followed the lead of companies providing workers’ compensation coverage in offering CPM. “Workers’ compensation providers are very good at covering this therapy because they recognize that return to work is faster,” Zieglar says. The ability to shorten recovery time by 2 months is significant in return-to-work claims. Getting a patient back to work in 3 months rather than 4 to 6 months is important to everyone, he says. “There is a huge amount of money saved, and the patient is back and healthy.” The end costs in time, pain management, and physical therapy are reduced. Some patients require very little or no physical therapy, just stretching and time in the CPM machine, Zieglar adds. “The people that I have seen that get stiff are miserable for 2 to 8 weeks until they can get some therapy to loosen up again.” Fighting that stiffness early also eliminates a setback in what PTs are trying to do-strengthen muscle around the joint. The result, Zieglar says, benefits everyone. Patients benefit because they are active in less time, payors pay less, andtherapists end up with a patient at 6 to 8 weeks who has good passive motion. “Now they can start working on re-strengthening and not have to start with a patient who is still very stiff.” email.
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.