Knee Anatomy: How The Knee Works

The knee is the most complex joint in the human body. It's made up of bones, ligaments, tendons and cartilages that work together to allow it to bend, straighten and rotate slightly from side-to-side.

The knee takes on a tremendous amount of stress, making it prone to injury. It may not be something most people think about, but just the act of climbing stairs puts 3-4 times as much pressure on our knees as standing. Hard to believe? Ask someone who's had a knee replacement!

We here at Simple Therapy want to dive into the anatomy of the knee and describe its basic parts in a way that's easy to understand. Knowing how the knee works will give you a better sense of its strengths and tolerances.

To do this, we'll simply break the knee down into four anatomical parts.

Knee Bones

The bones in the knee give strength and stability while walking, running, working or participating in sports. There are four bones.

1. Tibia "Shin Bone" - this bone connects the knee to the ankle. On top of this bone is located the tibial tubercle, a flat sort of surface where cushy, shock-absorbing cartilage called the meniscus is located.
2. Patella "Knee Cap" - the patella is designed to protect the knee joint.
3. Femur "Thigh Bone" - the femur is the largest, strongest bone in the body and connects the knee to the hip. On the bottom of the femur are two round knobs that connect to the tibia, forming the joint.
4. Fibula - the long skinny bone that runs parallel to the tibia and joins the knee to the ankle.

Knee Tendons

The knee is comprised of two tendons that help stabilize the knee. These tendons are extremely sturdy.

1. Quadriceps Tendon - this large tendon connects the muscle of the thigh or quadriceps to the kneecap. As you straighten your leg and feel it with your thumb just above the knee cap, you will feel this tendon tighten.
2. Patellar Tendon - this large tendon (technically a ligament) connects the knee cap to the tibia.

Knee Ligaments

The most famous knee ligament is the Anterior Cruciate Ligament (ACL), thanks to the world of sports, but there are others that are also vulnerable to injury. Ligaments are like sturdy bands that connect bone to bone. They're great at keeping things in-line and tight, but they don't like to be stretched or they'll break. In total, there are four knee ligaments.

1. Anterior Cruciate Ligament (ACL) - connects the femur to the tibia through the center of the knee joint. Prevents the forward movement of the tibia.
2. Posterior Cruciate Ligament (PCL) - connects the femur to the tibia and crisscrosses behind the ACL through the center of the knee joint. Prevents backward motion of the knee.
3. Medial Collateral Ligament (MCL) - connects the inner side of the femur to the inner side of the tibia. Prevents sideways motion of the knee.
4. Lateral Collateral Ligament (LCL) - connects the outer side of the femur to the outer side of the tibia. Also prevents sideways motion of the knee.

Knee Cartilage

Knee cartilage is the lubrication, so to speak of the knee. It keeps things soft and cushy. Since it has a very limited blood supply, it's not very good at repairing itself. Cartilage wears over time, so the older you get the more pain you are likely to experience in your knees and other joints. There are 3 cartilages.

1. Medial Meniscus - located on the inside of the knee joint, this piece of cartilage is crescent-shaped and acts as a cushion between the femur and tibia.
2. Lateral Meniscus - similar to the medial meniscus, only it is located on the outside of the knee joint.
3. Articular Cartilage - in every joint of the human body, there's a slippery fluid created by the joint lining that allows the bones to move against each other without friction.

Each part of the knee plays a crucial role in stabilization and comfort. To prevent injury to your knees, know your body's limits. Train consistently and eat a balanced diet in preparation for athletic events.

If you experience any swelling, pain, or tenderness in the knee, contact a health professional to find out how to relieve these symptoms.

Simple Therapy is an exercise therapy company that specializes in home-based exercise programs for common joint aches and pains. The above image is not our own.