All About the Knee

All About the Knee

Because the knee is one of the most complex joints in the body, many different things can go wrong, which can cause you pain and hold you back from pursuing your passions. By learning a little bit about knee anatomy and how everything works together, you may be able to understand the source of your pain.

animated depiction of knee anatomy

How Does the Knee Work?

At first, the knee appears to be a simple, uncomplicated part of the body. The truth, however, is that the knee is actually a complex mechanism with so many different parts that must work together harmoniously to provide the kind of mobility that most people take for granted every day.

The knee itself is actually comprised of four separate joints: one that joins the patella (the kneecap) and the femur (the thigh bone), two joining the tibia (the shin bone) to the femur, and one connecting the tibia and the fibula (a smaller bone in the lower leg).

Due to the complexity and the fact that it’s a weight-bearing joint, it may be more likely to be injured than any other joint in the body.

What Are the Parts of the Knee?

While your knee might seem like a small part of your body, it’s what helps you walk, run, jump, stand, sit and go up and down stairs — allowing you to get around and giving you the freedom to go where you want. It kind of works like the hinge on a door, while also allowing for some internal and external rotation. Knees are made up of many different parts, including bones, tendons, ligaments, cartilage and muscles, all of which help it to function.

Learn more about each part and what function it plays:


Your knee consists of three main bones: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). The femur supports your weight during standing, walking and running, and is covered in cartilage where it meets the tibia and patella. The tibia is the primary weight-bearing bone and connects to the bottom of the femur. Lastly, the patella sits on the front of the joint.


The muscles in the front of your thigh are your quadriceps, while the muscles in the back of your thigh are your hamstrings. To straighten your knee, you contract the quadriceps. To bend your knee, you contract the hamstrings.


Ligaments are the strong bands of tissue that keep the ends of the bone connected, and there are four major ones in the knee: the medial collateral ligament (MCL), the lateral collateral ligament (LCL), the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL). The MCL and LCL are on the sides of your knee and prevent it from moving too much in a side-to-side direction, while the ACL and PCL are in the front and back, respectively, and regulate the front-to-back bending of the knee.


These tough bands of soft tissue are kind of like ligaments, but instead of connecting bone to bone, they connect muscles to bones, which provides stability to the joint. When ligaments in the knee are torn or ruptured, tendons are sometimes used as grafts to replace the damaged ligament.

Articular Cartilage

Articular cartilage is a tough, rubbery, shiny material that covers the ends of the bones and serves to absorb shock, while providing a smooth surface to facilitate motion. When healthy, it provides a mechanism that has almost no friction, so the joint can bend freely.


The menisci are rubbery, crescent-shaped sections of fibrocartilage around the bone that fill the space between the round femur and the flat tibia. They help to absorb shock, spreading stress around the joint, while also providing a softer, smoother surface to protect the articular cartilage from wear.

Bursae and Synovial Fluid

The bursae are fluid-filled sacs that act as cushions that can provide gliding surfaces to reduce friction between the bones, tendons and muscles which is filled with synovial fluid, a thick liquid that also acts as a lubricant inside the joint.


Important Safety Information

As with any medical treatment, individual results may vary. The performance of knee replacements depends on your age, weight, activity level, and other factors. There are potential risks, and recovery takes time. People with conditions limiting rehabilitation should not have this surgery. Only an orthopaedic surgeon can determine if knee replacement is right for you.

147313-200722 EMEA