Whoever described the human body as a marvel of engineering was clearly not talking about the knee. Design-wise, it's deeply flawed: To function properly, more than a dozen tendons, ligaments, and bones must work in concert. Despite this complexity, the knee rotates in only two directions, forward and backward — great for when our forebears sprinted across African savannas, but not so hot when we pivot and swerve, or whatever it is you're doing every time you ski or play basketball. What's more, the joint wears out faster than the rest of the body, all but guaranteeing injury down the line.
That helps explain the growing queue for the operating room. In the past 20 years ligament reconstructions have risen 40 percent; in the past four years, knee replacements have jumped threefold. And it's not just aging baby boomers. "The fastest-growing segment for knee replacement is people under the age of 55," says Craig Della Valle, a professor of orthopedic surgery at Rush University Medical Center in Chicago.
Yes, knee surgery has come a long way. Procedures are now quick and minimally invasive, and recovery is measured in weeks versus months. But surgery is still surgery. And some procedures — say, repairing a torn meniscus or cartilage — are often no more effective than physical therapy. In too many cases, patients are actually worse off post-op.
Fortunately, there are easy things you can do to avoid the OR. Research shows that new knee-focused exercise routines can reduce injury risk by nearly half. Specific maintenance screenings go a long way to protect knees over decades. And if you're already injured, certain high-tech treatments can be worthy alternatives to getting surgery.
By taking control of your knee health, you're essentially making up for a hiccup in human evolution. When our ancestors evolved to walk on two legs, the upright stance changed the alignment of the neck and spine, imposing new forces on the knees — up to four times the body's weight. To absorb the burden, our bones lengthened, the hips narrowed to provide balance and stability, and the knee joint grew bigger — changes that occurred slowly, over the course of thousands of years. "We took a chimpanzee-like knee and turned it into a biped's," says Bruce Latimer, a physical anthropologist at Case Western Reserve University. "But evolution can't create perfection — it's merely a tinkerer that builds on previous variations."
That's not the only problem. The current model of the human body, Latimer adds, was designed to last only 50 years. "We doubled our life expectancy in a relatively short period of time," says Nicholas DiNubile, an orthopedic surgeon in Philadelphia and author of FrameWork for the Knee. "Evolution is not fast enough to give you a skeletal structure that will last as long as you do."
HALF OF PATIENTS GETTING KNEE REPLACEMENT SURGERY ARE UNDER THE AGE OF 55
In fact, by the time we enter our thirties, a series of chemical and cellular changes begins, which increases the likelihood of injury. We lose about 1 percent of bone density a year, which makes joints more brittle. Cartilage retains less water, becoming thinner and less elastic and providing less of a buffer between bones. And putting on weight — most of us add a pound or more a year — makes all of this worse. "It's not just pressure from the pounds, it's also the chronic inflammation that more fat creates," says DiNubile. "Think of it like rust in your joints, causing microscopic damage."
Worse still, old injuries plague the knee. A meniscus tear in high school, or cartilage wear from running in your twenties, boosts risk of arthritis or degenerative pain as you age. Nearly half of those who damage a knee will develop arthritis within 10 years of the original injury. "The number one predictor of injury is a prior injury," says Joe Hart, a sports medicine expert at the University of Virginia.
Exercise is supposed to help. But unless it's done right, it can make things worse. Some of us, for example, work out sporadically, jumping into an intensity we're not ready for and making it easy to snap or pull tight and little-used tendons and muscles. Others exercise regularly but fail to change things up — say, jogging the same four-mile loop or doing a weight routine over and over. "Do the same thing all the time and you can develop inflammation from overuse," says Mary Ann Wilmarth, a physical therapist in Andover, Massachusetts. And if you're not challenging the muscles in the legs and around the hips — essential for supporting the knee — with a mix of activities, Wilmarth adds, injury risk soars.
Finally, there's the hottest trend in fitness: high-intensity interval training (HIIT). Iñigo San Millan, an exercise physiologist at the University of Colorado School of Medicine, spent seven years studying HIIT injuries; he was shocked to find that recreational exercisers overtrain as much as the pros, blasting through HIIT workouts four or five times a week instead of the recommended twice a week. This leaves no time for muscle fibers and connective tissue to recover.
So what can you do? While you can't change your knee's build or the inevitable deterioration of aging, you can strengthen the joint and tissues — and pretty quickly, too. Here's exactly what you need to know to get another couple of decades from your knees.