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 better understand the cause of Knee Osteoarthritis and how treatment options may help.

grandfather with grandchild

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 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’s more likely to be injured than any other joint in the body.

doctor showing xray to patient

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:

BONES

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.

MUSCLES

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

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.

TENDONS

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. The largest tendon in the knee is the patellar tendon, which connects the patella to the tibia. 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.

MENISCUS

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 & SYNOVIAL FLUID

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

How Does Knee Osteoarthritis Affect the Structure of the Knee?

In the knee, the development of osteoarthritis tends to weaken the articular cartilage by breaking down its composition. Depending on the extent of the osteoarthritis, the cartilage can further thin and wear away, damaging its integrity. Knee Osteoarthritis can also cause meniscus damage due to surrounding soft tissues, tendons and ligaments undergoing stress. Meniscus damage can lead to further loss of stability and function in the knee.

Furthermore, the composition of the synovial fluid to lubricate the knee joint may be significantly decreased as a result of Knee Osteoarthritis.1

patient holding knee

References

1. Garrett Hyman, MD, MPH. 2021. What Is Knee Osteoarthritis?. [ONLINE] Available at: what is knee osteoarthritis. [Accessed 02 June 2021].

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This information is intended for residents of Australia only.

The information on this site is for educational purposes only and is not medical advice. Always talk to your doctor before you make decisions about your health.

© 2021 Johnson & Johnson Medical Pty Ltd. This site is published by Johnson & Johnson Medical Pty Ltd which is solely responsible for its contents. DePuy Synthes is a business unit of Johnson & Johnson Medical Pty Ltd. 1-5 Khartoum Road, North Ryde, NSW 2113, ABN 85 000 160 403.