February 13, 2012
Knee Replacement Surgery on the Rise
By Carolyn Gutierrez
For The Record
Vol. 24 No. 3 P. 24
Aging but still active baby boomers and escalating obesity rates have led to more people going under the knife.
Due to a complex array of often contradicting factors, including shifting attitudes toward aging and an ever-growing obesity epidemic, the number of knee replacement surgeries, also known as knee arthroplasties, is on the uptick. More than 600,000 knee replacements are now performed each year in the United States, according to the Agency for Healthcare Research and Quality (AHRQ).
The knee contains three compartments: the medial (inside area), the lateral (outside of the knee), and the patella-femoral (area under the kneecap). The knee comprises the lower end of the thighbone (femur), the upper end of the shin bone (tibia), and the knee cap (patella). The articular cartilage, which lines the joint surface, protects and cushions these bones during movement.
There are three types of arthritis that can result in chronic knee pain and disability: osteoarthritis, rheumatoid arthritis, and posttraumatic arthritis. Osteoarthritis occurs when the cartilage that cushions the knee bones wears away, creating stiffness and pain within the joint. This is generally age related, but the obesity epidemic has created an alarming rise in pre-Medicare-aged osteoarthritis patients.
Rheumatoid arthritis of the knee develops when the lubricating synovial membrane surrounding the knee joint becomes thickened and inflamed. The inflammation typically leads to pain, stiffness, and cartilage loss.
Posttraumatic arthritis is the result of a serious knee injury. Because the knee is the largest joint in the body, it is a common source of impairment for athletic patient populations. Bone fractures and ligament tears can compromise the knee’s articular cartilage, limiting joint mobility and causing pain and stiffness over time after the initial injury.
Aging Baby Boomers
According to Giles R. Scuderi, MD, vice president of orthopedic services for the North Shore-Long Island Jewish Health System in New York, “Total knee replacement has been on the increase—it’s almost exponential in the number of cases that are being done. If you think about the indications—you’re looking at different patient populations—there’s been an increase in the younger patients especially. Why is that? Because the baby boomers are aging. They’ve been a very athletic, mobile population. They want to have the best function possible to try to maintain an active lifestyle.”
Baby boomers are the patient population most likely to develop posttraumatic arthritis. After years of nonoperative courses of treatment for disabling knee pain, baby boomers are turning to total knee replacement surgery to maintain their vigorous lifestyle.
“If you look back—I believe it was 2003,” says Scuderi, “the National Institutes of Health actually published a consensus statement that basically said that total knee replacement was a very successful procedure for this group of patients. And since then, we’ve definitely seen a large number of patients undergo replacement. Looking at the results, over 90% of the patients who undergo total knee replacement do have an improvement in their quality of life. About 85% of the patients are satisfied with the results.”
According to data from the AHRQ, people between the ages of 45 and 64 were more than twice as likely to have had knee replacement surgery in 2009 than in 1997.
Mary I. O’Connor, MD, chair of orthopedic surgery and an associate professor of orthopedics at the Mayo Clinic in Jacksonville, Florida, notices strong generational differences in her patients’ attitudes toward their arthritis pain and mobility. When faced with severe functional limitations caused by arthritic knees, the older World War II generation—now in their 80s and 90s—is more inclined to “toughen up” or “soldier on” and accept their functional limitations, whereas the younger generations of older people, the first group of baby boomers, want to maintain their mobility.
“[The baby boomers] don’t want to use a cane, they don’t want to use a walker; they want to try to stay as useful, functional, and as independent as they possibly can,” O’Connor says. “They are more open to surgical treatments that would improve their function, whereas the WWII generation folks, it has to be really bad before they agree to surgery. They will put up with more, in my opinion. And so some of them will never have surgery because they don’t think [the knee arthritis is] bad enough, whereas someone 10 or 15 years younger than them will say, ‘I’m not willing to accept that I can’t play doubles tennis or I can’t golf. I want to still be able to do those things.’ The World War II generation patient will say, ‘It’s OK. I just won’t do those things anymore.’”
The Obesity Epidemic
Another probable factor in the rise of knee replacement surgery is the obesity epidemic. Unlike the stereotypical health-conscious baby boomer whose knees have suffered from years of injury, the obese patient tends to experience a vicious circle of inactivity leading to early osteoarthritis, which in turn leads to more inactivity. Many of the younger patients getting knee replacement surgery are overweight or obese.
“The National Institutes of Health has made a statement that one of the predisposing factors to osteoarthritis on the major weight-bearing joints, especially the knee, is obesity,” says Scuderi. “Greater load over that knee joint, wear and tear on the articular cartilage, leads to degenerative arthritis. That is another variable that has been well proven to be a cause for arthritis.”
Population-based studies have consistently shown a link between obesity and osteoarthritis of the knee. According to data from the first National Health and Nutrition Examination Survey, obese women had approximately four times greater risk of osteoarthritis than nonobese women. In the Framingham Study, overweight people in their 30s were shown to have a higher risk for developing osteoarthritis later in life than nonoverweight individuals. It was noted that losing weight could actually modify the results. As the overweight people shed weight, their risk of developing osteoarthritis seemed to decrease significantly.
“Obesity contributes to arthritis,” says O’Connor. “Arthritis then contributes to obesity because the patients can’t get up and move around. The top medical conditions that affect people in this country—heart disease, diabetes, hypertension, obesity—all of these are exacerbated and potentiated by arthritis because people don’t exercise.”
A small 2010 study from Finland suggests that the obesity itself is likely to create complications when heavy patients undergo total knee replacement surgery. The researchers followed 100 total knee replacement patients who were categorized according to their body mass index. Obese patients were more likely to have wound infection, phlebitis, nerve injury, and edema after surgery compared with nonobese total knee replacement patients. Their range of motion was also compromised when compared with the nonobese patients.
For many orthopedic surgeons like O’Connor, the driving issue behind the majority of the country’s musculoskeletal diseases is a basic lack of exercise. “We need to have a national campaign on activity,” says O’Connor. “I’ve been cochair of a national summit that we’ve had for the past two years called Movement Is Life. And the thing that’s different about this activity that I’ve been honored to cochair is that we’ve gotten stakeholders from across the spectrum. It’s not just orthopedic surgeons and primary care doctors but nurses and physical therapists, community leaders, and clergy, too. We’re asking what can we do to try and impact the burden of musculoskeletal disease on the American population. How do we develop effective programs that are going to get people to be active?”
Knee Replacement Surgery and Women
Recent studies have shown that women are at greater risk than men for osteoarthritis of the knee. Obesity in women compounds this risk. “We have data that show that even if women are only 15 lbs heavier, their risk of getting knee arthritis increases,” says O’Connor.
Data from the AHRQ indicates that the rate of hospitalization for women aged 45 to 64 undergoing knee replacement surgeries increased 157% between 1997 and 2009. (The rate for men increased 144% during the same time period.)
“Once they get past 65,” O’Connor notes, “the risk for developing knee arthritis is much higher for women than men. You would think logically there must be some correlation to menopause, but we don’t understand what it is. I’m the principal investigator of a study that is actually trying to look at whether we can identify biological differences in knee arthritis between men and women to try and understand why women get more knee arthritis than men.”
Because of the escalating number of female knee replacement patients, arthroplasty technology is keeping pace with gender-specific designs. Scuderi has been on several design teams for modern knee implants, including the Zimmer Gender Solutions High-Flex Knee.
“It’s an implant designed specifically for women,” says Scuderi. “It comes in different shapes as well as sizes to accommodate the female knee anatomy. The companies designing these products have addressed this shape and size issue by offering more sizes in their implants, increasing the inventory of component parts that are available. Our goal is to try to match the patient’s anatomy.”
Constant refinements of the high-grade plastics used in knee replacement implants are improving their potential longevity. “We’re trying to design implants that have better wear characteristics and improved fixation,” Scuderi says.
Currently most patients can expect their knee implant to last approximately 20 years. The durability of the newer implants makes them a more attractive option for younger patients.
To achieve a streamlined fit and a more natural feel to the implant, technologies such as patient-specific instrumentation are transforming traditional knee replacement surgery.
“Patient-specific instrumentation is where a CT scan or even an MRI is taken preoperatively. The anatomy of the patient’s knee is then developed into a computer model,” Scuderi explains. “Engineers and surgeons then review the computer model and find an implant that is the right size and shape for that particular patient. They can plan the surgical procedure preoperatively on the computer—almost virtual surgery—so that instruments are specifically designed for that patient to be brought into the operating room, and therefore you have a patient-specific surgery. This is the technology that is evolving and coming about in that regard.”
Robotically assisted knee replacement surgery is also a burgeoning orthopedic technology. Using a robotic system that includes real-time video imaging of the inside of the knee, surgeons are able to perform a less invasive knee surgery by making smaller incisions yet allowing a more precise alignment when placing the implant. Robotically assisted technology is more frequently used for partial knee replacement surgeries, which are typically done when only one or two sections of the knee have significant arthritis, usually the medial section. Partial knee replacement is helpful in that it can serve as a bridge for 10 to 15 years until the patient’s knee becomes arthritic enough to warrant a total knee replacement.
“The advantage of a partial knee replacement,” says O’Connor, “is that it feels more like your knee because we keep more of your knee. If you have a patient who has a total knee replacement on one side and a partial knee replacement on the other, nine out of 10 times that patient’s going to say they prefer the partial knee replacement.”
“There are clear risks with either partial or complete knee replacement,” says O’Connor. “You have to seriously weigh the risks vs. the benefits. The thing that I talk to patients about first is risk of infection. I bring up infection first because it is one of the most serious complications even though the risk is very low.”
Although the risk of infection is less than 1% during knee replacement surgery, it can have devastating consequences. When there is an infection, surgeons have to remove the implant, put in a spacer, administer IV antibiotics for six weeks, and then completely redo the surgery.
Blood clots are a more common complication associated with the procedure. Guidelines established by the American Academy of Orthopedic Surgeons recommend that patients be put on pharmacologic agents such as warfarin or enoxaparin to avoid postoperative blood clots. Aspirin is often administered as well. Sequential stockings or sequential foot pumps can help prevent blood clots, blood pooling, and fluid buildup in the lower legs.
Other postsurgery risks include possible nerve damage on or surrounding the knee, problems with the implant such as loosening, and continued knee pain.
“I tell [my patients] there’s a risk that they’re going to still have some pain,” says O’Connor. “Of course they don’t want to hear that, but they need to hear that because the knee replacement is still not the same as a normal knee. What we have is not as good as what the patient had when they were 16 or 20. It’s better than the arthritic knee that the patient had at the time of surgery, but it’s important that the patient understand what the surgery can do for them.
“We talk about expectations. I ask them, ‘What is it that you believe this surgery will allow you to do that you’re not able to do now?’ If they tell me that they want to run marathons, then we have to have a serious discussion about how long knee replacement is going to last and do they really want to do that. It’s important that the patient has a good understanding of what the surgery can do and that their expectations are realistic in terms of scope.”
The Rehabilitation Process
After knee replacement surgery, patients remain in the hospital for approximately three days. During that time, early mobilization is encouraged. Twice-per-day workouts with a physical therapist typically begin the morning after surgery. Patients are encouraged to try bending their knee to work on their range of motion.
At some hospitals, a continuous passive motion device is used to bend the knee while patients are still in their bed. Patients may start out with a walker for a day or two then gradually progress to crutches or a cane depending on their strength and mobility.
Upon discharge, patients who go home sometimes receive physical therapy from a visiting nurse. Older patients may go to a rehab facility for several days of inpatient physical therapy. The goal is to increase strength and walking distance.
Recovery from arthroplasty can take anywhere from six to 12 weeks. “The people that are in better shape, their recovery is easier,” says O’Connor. “The people that are more debilitated, their recovery is a lot longer. The patients have to be motivated.”
— Carolyn Gutierrez is a freelance writer based in New York City.