Knee Anatomy

The knee is a complex joint that connects the thigh to the shin. The knee joint allows for various movements such as flexion (bending), extension (straightening), and slight rotation. The knee joint is composed of several structures:

Femur: The thigh bone, which forms the top part of the knee joint

Tibia: The shin bone, which forms the bottom part of the knee joint

Patella: The kneecap, a small bone located in front of the knee joint. It protects the knee and provides leverage for the thigh muscles (quadriceps). The patella moves on the front part of the femur in a groove called the “trochlea groove”.

Muscles are structures that move the joint. For a muscle to move a joint it must cross the respective join

The knee muscles form three major groups:
Quadriceps Muscles: A group of four muscles located at the front of the thigh which work together to extend the knee
Hamstring Muscles: Located at the back of the thigh, these muscles help flex the knee
Gastrocnemius and Soleus: Calf muscles that cross the knee joint and assist in knee flexion.

Quadriceps Tendon: Connects the quadriceps muscles to the patella

Tendons are thick tissue structures that connect muscles to bone

Patellar Tendon: Connects the patella to the tibia. It is also called the patellar ligament as it connects two bones.

 The knee joint, like any other joint in the body is covered by articular cartilage

Articular Cartilage: Covers the ends of the femur, tibia, and back of the patella. It provides a smooth, gliding surface for the bones to move against each other, reducing friction and allowing for seamless movement. Wear of this articular cartilage is defined as arthriti

In addition to articular cartilage, the knee joint contains two structures called meniscii

Meniscus: Two C-shaped wedges of cartilage on the inner (medial meniscus) and outer part (lateral meniscus) of the joint, located between the femur and tibia. They are similar to the articular cartilage but are more rubbery in consistency. They act as shock absorbers, distribute weight, and enhance stability in the knee joint. Their primary function is to protect the articular cartilage from wear and tear.

Ligaments are tissue structures that connect one bone to another. Their main function is to provide stability to a joint. There are four main ligaments in the knee joint that run between the femur and the tibia

Anterior Cruciate Ligament (ACL): Located in the center of the knee, it prevents the tibia from sliding too far forward and provides rotational stability

Posterior Cruciate Ligament (PCL): Also located in the center of the knee, it prevents the tibia from sliding too far backward

Medial Collateral Ligament (MCL): Runs along the inner side of the knee, providing stability and preventing excessive inward movement (valgus stress)

Lateral Collateral Ligament (LCL): Runs along the outer side of the knee, providing stability and preventing excessive outward movement (varus stress)

The anterolateral ligament (ALL) runs along the outside of the knee and is ofen injured at the same time as the ACL

Medial Patellofemoral Ligament (MPFL) is an additional ligament that runs between the inner part of the femur to the inner border of the patella. It provides stability to the patella in its movement at the front of the knee.

Understanding the anatomy of the knee is essential for diagnosing and treating injuries and conditions affecting this joint.