More than just a simple hinge, the knee is stout pillar of muscles, bones, ligaments, and cartilage that endures an extra ordinary pounding everyday. When you walk down a staircase, for instance, your knees support a force that is equivalent to 4 1/2 times your body weight. Jump, and your knees absorb a vertical impact that is equal to 7 times your body weight.

The knee is the strongest joint in the body. It has a very remarkable design that is meant to stand up a lot.

Three bones – the femur (thighbone), the tibia (shinbone), and the patella (kneecap) – form the knee, the largest and most complex joint in your body. The ends of these three bones are covered with cartilage called articular cartilage and are interspaced with meniscus cartilage. A tough, elastic material that helps absorb shock and prevents the bones from rubbing against each other, cartilage allows your knees to bend and swivel. This mechanism is bound together by a snarl of ligaments, tendons, and muscles, including the quadriceps, the strongest group of muscles in your body, which are attached to the kneecap.

Yet as sturdy as it seems, the knee is actually one of the most vulnerable joints in the body, particularly among people older than 60. In fact, more than 600,000 seniors seek medical care for knee problems each year, according to the National Center for Health Statistics.

Your knee is particularly susceptible to injury because, unlike your hip, it isn’t well-protected by muscle or fat. Bursitis, tendinitis, infections, cysts, and chondromalacia – a softening of the cartilage on the back of your kneecap – also can trigger immobilizing knee pain.

But by far, the most common cause of knee pain is osteoarthritis, a degenerative joint disease that affects more than 20 million Americans, most of them over age 45. As osteoarthritis progresses, the cartilage that protects the bony structures in your knee wears down, allowing bones in the joint to literally gnash against each other, causing pain and loss of mobility.

A one-time knee pain usually isn’t a problem. But if it is ongoing, it should be checked out. The earlier you find out what is causing your knee pain, the more that can be done to correct the problem and prevent it from getting worse. So see your doctor if:

  • Your knee pain or stiffness lingers for more than a week.
  • Your pain is severe or unexplained.
  • Your knee is hot, red, swollen, or painful.
  • You feel pain radiating down your leg.
  • You have recently inured the joint, particularly with a sharp blow.
  • Your knee swells following activity.

Often, knee pain can be relieved without surgery. In fact, once you are diagnosed, your doctor may suggest some of the simple non-invasive strategies.