Like the inner workings of an engine, knees are complicated, says Arturo Peal, who teaches yoga, anatomy, kinesiology, and therapeutic touch in New Orleans. “As the midway point between feet and hips, knees are responsible for translating your movement through the world, absorbing the pressures of gravity, and buffering the impact of walking and jumping. When they function well, they are shock absorbers.” And just like the shock absorbers on your car, they can wear out.

The key to the smooth operation of these vital joints: understanding how they work so you can treat them with care.

See also: Still Icing Your Creaky Knees? These Poses Are a Better Fix

Knee anatomy

The knee is a hinge joint; it extends forward and back. Four bones make up the joint: the femur (thigh bone), tibia (inner shin bone), fibula (outer shin bone), and patella (kneecap). The first three form the main knee joint, the tibiofemoral joint. At the front of the knee, the patella, which is shaped like a shallow saucer, rests in a groove on the front of the femur to form the patellofemoral joint.

Two C-shaped pieces of tough, rubbery, cartilage called menisci provide cushioning between your tibia and femur. Tough fibrous ligaments connect the bones, control the knee’s movement, and keep the joint strong and stable. Along with the knee tendons—strong tissues that connect muscle to bone—these ligaments stabilize the knee and limit sideways movement. (If your knee ever moves significantly left or right, it’s likely injured and should be looked at by a professional.) The synovial capsule surrounds the knee and is filled with synovial fluid, which nourishes and lubricates the joint so it can move freely.

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