Knee Anatomy

Femur (Thighbone)

The femur is the longest bone in the human body, and it makes up the top part of the knee joint. The bottom end of the femur has two rounded knobs (known as condyles), which rest on top of the tibia. It also has a groove on the front known as the trochlea, where the kneecap glides as you bend and straighten your knee.

Tibia (Shinbone)

The tibia is the larger of the two bones in your lower leg, and it makes up the bottom part of the knee joint. The top of the tibia is flat and supports the femur.

Patella (Kneecap)

The patella is a small, flat, circular bone that is embedded in the tendon of the quadriceps muscle. It slides up and down a groove on the front of the femur as the knee bends and straightens.

Fibula

The fibula is the other bone in your lower leg, that goes from the outside part of your ankle all the way up to just below the knee joint. Ligaments that are crucial to the stability of your knee attach here, and can be damaged with certain injuries.

Meniscus

These are two crescent-shaped discs of tough, rubbery cartilage that sit between the femur and the tibia. They act as shock absorbers, cushioning the impact between these two bones when you walk or run. They frequently can become torn with an acute injury, or over time with wear and tear. When this causes pain, they may need surgery to repair or trim.

Articular Cartilage

This is a smooth, slippery substance that covers the ends of the femur, the top of the tibia, and the back of the patella. It helps these bones glide smoothly over each other as the knee moves. When the cartilage is damaged from an injury, your knee surgeon Dr. Mayo can perform cartilage preservation surgery to help the knee maintain it’s function.

Ligaments are strong, elastic bands of tissue that connect bones to each other. There are four main ligaments in the knee:

Anterior Cruciate Ligament (ACL)

The ACL is located in the center of the knee. It controls rotation and forward movement of the tibia. Because of its location and blood supply, the ACL has a poor ability to heal on its own. This is the most frequent ligament tear seen that requires an ACL reconstruction surgery in athletes.

Posterior Cruciate Ligament (PCL)

The PCL, also in the center of the knee, controls the backward movement of the tibia. Though less commonly injured, when there is a complete tear surgery may be needed to restore stability to the knee.

Medial Collateral Ligament (MCL)

The MCL runs along the inside of the knee. It resists forces acting on the side of the knee. The MCL is the most frequently injured ligament in the knee, but very rarely requires surgical intervention.

Lateral Collateral Ligament (LCL)

The LCL runs along the outside of the knee, resisting forces from the side of the knee. It is one of the major components of the posterolateral corner complex, which provides rotatory stability to the knee and can sometimes be damaged with other knee ligament injuries.

Tendons are tough bands of tissue that connect muscles to bones. The most important tendon in the knee is the patellar tendon. This tendon connects the quadriceps muscle, a powerful muscle at the front of the thigh, to the tibia via the patella. These can rupture if they see excessive loads, which will cause significant pain, weakness, and knee dysfunction.