Knee pain examined
DEAR DOCTOR K: I’ve been having a lot of knee pain. Would you describe the anatomy of my knee so that I can understand more when I see my doctor about it?
DEAR READER: Joints are places where two or more bones meet, to allow a part of your body to move. And the knee joint is a remarkable structure. It is a complicated network of bones, cartilage, muscles, tendons and ligaments. These structures, working together, allow us to walk, kick, squat, stand back up and do the Twist. (I know that’s a dated reference!)
I’ve put an illustration of the knee on my website, AskDoctorK.com. It will help you to look at this illustration as I describe the various parts of the knee and explain what they do.
Three bones meet at the knee joint: the thigh bone (femur), the shin bone (tibia) and the kneecap (patella). All of your weight above your knee is supported by it. That means your knee joints have to be strong as well as flexible.
At its lower end, the femur divides into two rounded knobs called condyles. The lower end largely rests on the top end of the main bone of the lower leg, the tibia. The top of the tibia is rather flat with a middle bump. That bump fits in the space between the two rounded condyles. The mismatch in shape — like two doorknobs balanced on an uneven plate — allows for complex movements (like doing the Twist). But it makes the knee potentially unstable.
The patella is a small, flat bone that floats in front of the knee joint. It protects other knee structures and applies leverage to help straighten the joint.
Separating the bones of the knee are two rubbery, tough, elastic cartilage pads known as menisci. They curve around each side of the top of the tibia, serving as shock absorbers. They help the bones fit together.
Muscles in your calf and thighs power the movement of your legs. Tendons connect muscle to bone and transfer muscle power to the bone to create movement. For example, a tendon connects the quadriceps muscle in your thigh to the patella, providing the power to extend your leg. These movements change the position of the knees. They also affect the parts of the knee joint that bear most of your body weight.
The several different ligaments of the knee help keep it stable. Ligaments are tough, fibrous tissues that connect bones or cartilage at a joint. They allow movement within a safe range. If you’re a sports fan, you’ve probably heard of the anterior cruciate ligament, or ACL. A tear of this ligament is a common sports injury. The ACL connects the femur to the tibia in the center of the knee.
Synovial fluid lubricates the knee joint. It minimizes friction as the joint components rub against one another. It also forms a seal that allows neighboring bones to slide against each without pulling apart.
I hope this information will help you when your doctor examines your knee and explains what’s wrong.
(Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.)