Bones in the Knee

By Tristyn Kinser, MS, ATC, LAT

What Type of Joint is the Knee?

The knee is a large hinge joint that allows the bending and straightening of the lower leg. This joint allows for about 120 degrees of flexion, which helps the body with walking, jumping, running, and sports. The Knee is a complex joint, made up of bones, ligaments, tendons, muscles, cartilage, and bursae.

The bones in the knee joint are: the femur, patella, tibia, and fibula.

Bones in The Knee anatomy as well ass knee ligaments and muscles BY JOI REHAB

Image of The Anatomy of the Knee

What Are the Bones Under the Knee?

The two bones located under the knee are the Fibula and the Tibia. The knee bone or kneecap is also known as the patella.

The Femur

The femur, most commonly referred to as the thigh bone, is the longest and strongest bone in the body. The head of the femur is ball-shaped and fits into the pelvis, creating the ball-and-socket hip joint. The neck of the femur extends outward to create the greater and lesser trochanters which serve as attachment points for the glutes and other hip muscles. The body of the femur runs down the thigh to form the medial and lateral epicondyles which make up the sides of the knee.

The femur is one of the bones that has growth plates.

3D Illustration of Femur Bone Joints

The Tibia

The tibia also called the shinbone connects to the knee and ankle. It is a strong bone with a flat head that supports most of the body’s weight (about 80%). The head of the tibia is flat-shaped to allow it to form perfectly to the end of the femur so the joint will bend smoothly when walking and running. The tibia runs down the middle of the leg and ends at the small bump you can feel on the inside of the ankle, the medial malleolus.  The overworking the tissues that attach to the bone cause shin splints, and are a common injury.

Tibia bone from 4 views with distal and proximal ends

Tibia from multiple views

The Patella

The smallest bone of the knee is the patella. It’s a small, triangular bone that glides back and forth over the femur and tibia. The primary function of the patella is to serve as the attachment point for the large thigh muscle, the quadriceps (quads). The patella tendon secures the quadriceps to the patella, which helps to bend the knee and move the lower leg. A common injury in this area is called patellar tendinitis.  Repetitive stress can cause tiny tears in the tendon, this is usually from sports or exercise.

Picture of the knee cap

Picture of the knee cap

The Fibula

Lastly, the fibula is the long, skinny bone fixed along the outer portion of the lower leg, opposite the tibia. The fibula runs from the outside of the knee to the ankle, creating a large bump on the outside of the ankle, called the lateral malleolus. The primary role of the fibula is to serve as a muscle attachment. Fascinatingly, the fibula only bears about 20% of the body’s weight, leaving most of the heavy lifting to the tibia.


The knee is a hinge joint that bends and straightens the knee, allowing for all activities of daily life and playing sports. The knee has 4 bones; the femur, tibia, patella and fibula, and many soft tissues. Common injuries at these bones are patellar tendinitis and shin splints which can be easily treated with physical therapy.

Injury to the bones, muscles, tendons, ligaments, bursae or the meniscus may cause pain in the knee. If you are having knee pain, JOI can help!

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By: Tristyn Kinser, MS, ATC, LAT

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