Is it time for a knee replacement?

Back in the day, going weak in the knees meant something good. Decades later, though, it's merely a glaring sign you may need to replace your natural knee joint — the largest in the body — with a metal and plastic version.

It's a growing phenomenon as the population ages and more people want to stay active as they grow older. Total knee replacement is one of the most common surgeries in the United States, performed in about 790,000 Americans each year — about 60% of whom are women.

What accounts for the sex gap? We're about 30% likelier than men to cope with arthritis in our knees — a propensity driven by factors such as hormones, joint laxity, and anatomical differences between the sexes. And arthritis pain happens to be the culprit that leads to most knee replacements, whether from wear-and-tear osteoarthritis, inflammation-driven rheumatoid arthritis, or post-traumatic arthritis stemming from an injury to the knee joint.

Ligaments in the knee can also loosen, causing the joint to bend inward or outward. Women also experience this complication more often than men, says Dr. Scott D. Martin, director of the Joint Preservation Service at Harvard-affiliated Massachusetts General Hospital.

But while women are more vulnerable to these knee-wrecking issues, we're also more apt to jump on the problem and be evaluated for joint replacement.

"Men are more reluctant than women to come and get treated," Dr. Martin says. "Women come in sooner, and they tend to be better at sticking with the treatment plan."

Taking the leap

You might have already coped with years of limitations — difficulty walking distances, climbing stairs, or getting in and out of chairs — related to your knee problems. Before knee replacement becomes an option, your doctor will likely require you to have tried every available noninvasive treatment. These include pain relievers; injections of medications such as cortisone and hyaluronic acid, which can dampen inflammation or lubricate the joint; and physical therapy.

Any of the following situations might suggest it's time to consider surgery:

Pain slows you down no matter what you've tried. You're hobbled by pain that hinders you from doing the most basic things. The effects aren't just physical. "If you've tried everything else, it starts to physically, mentally, and emotionally affect you on a daily basis," Dr. Martin says.

Your walking is unstable. As the day goes on, your legs may feel stiffer and weaker. Your knee may even buckle. "After you've been up for eight to 10 hours, your muscles get angry, so you're feeling every step," Dr. Martin explains. "It's not that the arthritis progressed in six hours, it's that the muscles are fatigued." Moreover, this raises your risk of falling.

You need multiple medications to function. Getting through the day may require taking several forms of nonsteroidal anti-inflammatory drugs (NSAIDs) or even prescription pain relievers. But age factors into your ability to continue this regimen indefinitely, Dr. Martin says. Someone in her 40s will likely draw this strategy out for many years, while others in their 60s or 70s may be spurred by their dependence on pain relievers to go ahead with the operation.

Knee-sparing strategies

Even if you have knee problems, you might be able to delay replacement surgery while you protect your knees from further damage. Here are some ways to buy time:

Consider a less-extensive operation. Same-day arthroscopic procedures enable surgeons to use a tiny camera to visualize problems inside the joint and trim away damaged tissues.

Wear a knee brace. This can stabilize the knee, but the approach has drawbacks. "Some people swear by them, but they don't treat the root cause of the problem," Dr. Martin says.

Use topical creams or pain patches. These products can offer targeted relief without side effects common to systemic medications. But pain patches are more effective for muscular pain around the knee than pain deeper within the joint, Dr. Martin notes.

Stay active. Regular exercise — especially low-impact activities like swimming, biking, and walking — keeps leg muscles strong, alleviating knee strain.

Lose weight. If you already have arthritis or a knee injury, carrying extra weight "can greatly accelerate the wear on that knee," he says. "Losing weight can take pressure off the joint."

If you're interested in learning more about knee replacement, consult Harvard's online guide Total Knee Replacement. This in-depth look will help you decide if knee replacement is right for you.

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