Maybe it was a high school sports injury that you never got around to treating. Or maybe it was that spill you took skiing last winter that still gives you problems today.

Whatever its cause and however long ago it happened, a knee injury can affect how well you move. Fortunately, you can usually treat it with physical therapy, weight loss, and other strategies. Sometimes, if it’s more serious, your doctor may suggest surgery.

But how do you know when an operation is your best choice? That's a discussion to have with your doctor. Surgery can't fix every knee problem, and not everyone is a good candidate.

The Telltale Signs

A three-part checklist can often tell whether your knee might benefit from surgery, says orthopedic surgeon Charles Bush-Joseph, MD, a professor at Rush University Medical Center and team doctor for the Chicago White Sox.

“If you have a persistent loss of motion so that you can’t bend or fully extend the knee, that’s one sign,” he says.

“If you can’t squat or bear your weight on your knee, that’s another sign.”

“And if you turn or twist a certain way and you hear a pop or it makes some kind of sound, that’s the third one.”

If you have only one of those three conditions, start with the basics: rest; physical therapy or some consistent, low-stress exercise; and maybe anti-inflammatory drugs. That may be all you need.

“If it’s two out of three, conservative treatment may be enough, but it may not,” he says. “If it’s three out of three, we think surgery is probably the best approach.”

Of course, the nature of your injury will drive the treatment that you need.

Meniscus Tear

The knee has two disc-shaped pieces of cartilage that cushion the bones in the joint. These are your lateral meniscus and medial meniscus.

When someone hears that he has a meniscus tear, he’ll usually assume he needs surgery, Bush-Joseph says. But that’s not always true. Many adults have at least a small meniscus tear, and these injuries don’t always make it hard to do daily activities or cause noticeable pain.

A tear in the outer part of the meniscus can sometimes heal on its own. It benefits from healthy blood flow, and even if surgery is needed, the structure of the meniscus can remain intact and heal completely.

The inner part of the meniscus doesn’t have the same healthy circulation. So it won’t really heal. If it tears, surgery usually just trims away the damaged part and patches what’s left back together.

Bush-Joseph calls this “cleaning out” the knee. Doctors can do this through arthroscopy, a type of operation that uses several small cuts, rather than open surgery that leaves a large scar.

“You’ll miss a day or 2 of work, take it easy for 2 to 6 weeks, and by 8 weeks, you’ll probably be back to full activities,” Bush-Joseph says.

Knee Ligament Sprains or Tears

These are common among athletes. There are two types of ligaments: collateral and cruciate. You have four main ligaments in your knee: the lateral collateral ligament, medial collateral ligament (MCL), posterior cruciate ligament, and anterior cruciate ligament (ACL).

Ligaments help keep the bones in your knee stable, but they are prone to injuries, particularly through contact or from changing direction suddenly when you’re running. Sports fans know that ACL and MCL injuries can sideline an athlete for months.

But for most people who don’t make their living running full speed or getting hit, it usually takes several weeks to recover.

It can take roughly 8 weeks to recover from surgery to repair a ligament tear. But if you need a major reconstruction of a torn ligament, it can take 6 months or so to get you back to full strength, Bush-Joseph says.

After Surgery: Prevention

Once you’ve had your operation and your doctor says you can get back to your usual activities, you should check with your surgeon about any changes you should make to prevent future injuries.

You may need to cut back on high-impact activities, such as those that involve contact or a lot of jumping. Have a frank conversation with your doctor about what’s OK and what you absolutely shouldn’t do.

Your doctor will probably recommend physical therapy after your surgery. In this type of rehab, you’ll learn exercises that will strengthen the muscles around the knee. Stronger quadriceps (muscles at the front of the thigh), for example, will help keep your knee stable.

Knee surgery to repair the meniscus or the ligaments does make you more likely to get osteoarthritis (the wear-and-tear type of arthritis) later in life. But most surgeries to repair knee injuries are successful. They improve knee strength and flexibility and ease pain.

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