Images of the Knee

The Knee Joint

The knee is one of the most commonly injured joints in the body. The knee joint is the junction of the thigh and the leg (part of the lower extremity). 

• The femur (thigh bone) contacts the tibia (shin bone) at the knee joint. 
• The patella (kneecap) sits over the front of the knee joint. 
• Four major ligaments connect the bones and stabilize the knee joint. 

In the image above, the physician is pointing to the anterior cruciate ligament, or ACL, one of these important ligaments.

Inside the Joint

Inside the knee joint is a smooth cover on the ends of the bone called articular cartilage. 

Between the articular cartilage layer, is a shock absorbing cushion called meniscus cartilage. 

When people talk about knee cartilage, they may be talking about either the meniscus cartilage or the articular cartilage.

Bones of the Lower Extremity

The lower extremity includes the femur, the tibia, and foot and ankle bones. 

We call the segment between the hip and knee the thigh, and we call the segment between the knee and ankle the leg. 

Some people confuse the words leg and lower extremity, but in anatomic terms the leg spans only the distance from the knee to the ankle.

AP Knee X-Ray

An X-ray is one of the most common imaging tests used to diagnose a knee problem.

The image here is a front-to-back view of the knee joint, also called the AP view. (AP stands for anteroposterior, meaning the image is directed from the front to the back of the knee joint.)

Lateral Knee X-Ray

While an AP X-ray looks from front-to-back of the knee joint, a lateral view looks from the side of the joint. 

Lateral X-rays are particularly helpful at seeing the kneecap, or patella, and the cartilage space behind the kneecap.

Knee Arthritis

Arthritis is a condition that causes pain and inflammation in joints.

Many different types of arthritis can occur in the knees, the most common of which is called osteoarthritis. People often use the words "wear-and-tear" to describe osteoarthritis, as it occurs when the cartilage between joints wears away, causing pain, stiffness, and trouble moving.

Knee Replacement

Knee replacement surgery is commonly used to treat pain and mobility issues caused by severe arthritis. 

During the procedure, damaged cartilage and bone are removed and replaced with a new implant, made of plastic or metal (or both), to restore the function of the knee.