Quiz: Know Your Knees

Kneecaps form while a baby is inside its mother's womb. They are made of cartilage and don't become bony until later. So, they don't show up well on X-rays. Girls' kneecaps start becoming bony when they are about 3 years old; boys' when they are 4 or 5. 

Only the hind legs of man's best friend have knees. Just like humans, Fido can have knee problems. A dog can tear the tissue that supports the knee by doing something as simple as jumping off a sofa. All it takes is a bad landing.

You can help protect your knees by warming up with dynamic stretches or walking before playing sports. If the large muscle in the front of the thigh is tight, the kneecap gets pushed up against the thighbone. Tight muscles on the back of the thigh force your muscle on the front to work harder; that, too, can cause pain.

Do your knees make noise? It could be your ligaments tightening as you move, or it could be the sound of rough surfaces gliding over each other. If your knee hurts when it pops, if it locks, or if you notice swelling or loss of function, get it checked out. 

Your kneecap, also called your patella, is the small bone in front of your knee. It connects the muscles of your thighbone and shinbone. The undersides of your kneecap (and the ends of your thighbone) are covered with slippery stuff that helps your bones glide smoothly as you move your leg. As you bend and straighten your leg, your kneecap gets pulled up and down. 

Your knees are the largest joints in your body. And they take on much more than just your body weight. Every time you walk, the force on your knees is three to six times your weight. Being overweight increases the stress on your knees. Obese women have nearly four times the risk of developing osteoarthritis in the knee; for obese men it's nearly five times. 

The “quarterback kneel,” the “victory formation,” and “to take a knee” all refer to a play in football. A coach might tell the quarterback on the leading team to drop on a knee to run out the clock, increasing the chances of winning. The phrase has other meanings and uses. Sometimes players will go on one knee as a show of respect to an injured player. 

Your thighbone, your shinbone, your calf bone, and your kneecap come together at your knee. Your kneecap is at the front of your knee joint. It's held in place by tendons, which are cords that connect muscles to bone or other muscles, and by strong bands of tissue called ligaments.

It's a weird feeling. Your doctor taps your knee with a small rubber hammer, and the lower part of your leg kicks out as if it has a mind of its own. It's called the knee-jerk reflex. The tap of the hammer stretches a tendon and the connected muscle in your thigh. The knee-jerk reflex is important: It helps you keep your balance.

Knee problems keep orthopedic surgeons hopping. They are the most common reason that people see orthopedic surgeons. Common knee problems include injuries to ligaments known as ACL, and the less common MCL and PCL. Changing direction quickly, slowing down when running, and landing from a jump can all cause tears in the ACL. MCL and PCL injuries are usually caused by blows to the knee. 

Doctors perform more than 600,000 knee replacement surgeries a year, and that number is expected to go up to more than 3 million by 2030. If you've had a knee replacement, you'll need to stay clear of exercises that put stress on that joint. Avoid tennis, squash, skiing, jogging, and contact sports like football and baseball. Dancing, golfing, and biking on level surfaces are all good options, as are swimming and walking. 

The friction of being on your knees irritates a small sac in front of the kneecap. When that sac becomes inflamed, it fills with fluid and causes swelling. Gardeners can have this problem, as can wrestlers, and football and basketball players. If you work on your knees, wear kneepads, and get up often to stretch.