Knee Joint anatomy - Patient Education Portal

The knee, the largest joint in our body, connects the thigh to the lower leg. Like all joints in the body, the knee is made up of cartilage, muscles, ligaments, bones, and nerves. Knee joints support body weight, allow legs to bend, and enable movements like walking, running, and jumping. Therefore, understanding the knee joint anatomy is important for gait assessment and diagnosis of joint diseases.

‍Type of the Joint

Our body is a well-organized machine with different moving parts. It has several kinds of joints that help them function cooperatively. Healthcare providers categorize joints based on what they are made of and what they do.

The knee is the biggest synovial joint that allows a wide range of movement. These joints are ingenious connections in our body, where one bone fits into a cavity in another bone, and to ensure smooth movement, the ends of these bones are coated with slippery cartilage. The distinctive feature of synovial joints is a fluid-filled sac that acts like a protective cushion, ensuring everything glides seamlessly with minimal friction.

When it comes to function, think of the knee joint as a door hinge. Just like a door swings open and closes on its hinges, the knee, being a hinge joint, works similarly, moving in one plane.

Anatomy

As mentioned earlier, the knee joint consists of bones, cartilage, ligaments, muscles, and nerves. To understand the complex anatomy of the knee joint we will take a look at each component separately.

Bones

Three main bones make up the structure of the knee: the femur, known as the thigh bone, the tibia, known as the shin bone, and the patella, or kneecap. They meet at places called articulations or articulating surfaces. The knee has two articulations:

Tibiofemoral articulation is the site where the lateral and medial surfaces of the femur connect to the tibia.
Patellofemoral articulation is the site where the patella attaches to the femur.

Cartilage

Cartilage is resilient and flexible connective tissue that plays an important role in safeguarding your joints, acting like a reliable shock absorber. Two types of cartilage keep your knees in good shape:

Hyaline cartilage, also known as articular cartilage, is the predominant type of cartilage found within the human body. It is a smooth lining that covers the joint surfaces and caps the ends of your bones where your femur, tibia, and patella come together. It is the friction-resistant layer that lets your bones glide effortlessly, creating a smooth movement in your joints.
Fibrocartilage, as its name suggests, is a tough type of cartilage composed of thick fibers. The Meniscus in the knee, composed of two wedges of fibrocartilage, acts as a cushion between the femur and tibia. It is like the shock-absorbing buffer that keeps your knee movements fluid and resilient. There are two types of menisci in our knees: medial meniscus, which has a C-shape and hooks onto the front and back areas of the tibia, and lateral meniscus, which is circular and serves as a safeguard of the lateral tibial plateau.

To sum up, cartilage ensures your joints remain protected and your movements stay smooth, keeping you comfortable and supported.

Joint capsule

The knee joint capsule is like a robust sheath made up of muscle tendons and their extensions, wrapping around the joint. It has an outer tough layer, connecting with nearby tendons, and an inner synovial membrane that acts like a lubricator, relieving friction and nourishing the cartilage.

The capsule also creates fluid-filled pouches called bursae – these are like knee joint lubricators, minimizing friction. Notable ones include:

The Suprapatellar Bursa lies above the patella and acts as a cushion between the femur and the tendon of the quadriceps muscle.
The Prepatellar Bursa is found in front of the patella, serving as a buffer between the skin and the kneecap.
The Infrapatellar Bursa lies under the patella, particularly between the patellar ligament and the tibia. It is like a protective pocket keeping things moving smoothly in the knee joint.

Ligaments

The knee joint capsule gets extra support from various ligaments, both inside and outside the capsule. They get tight when you straighten your knee to stop the leg from overextending, just like built-in safety nets that keep your knee from going too far.

Extracapsular ligaments lie outside the joint capsule and serve as a support system of the knee by stabilizing the patella and stopping it from displacement. These ligaments also play an important role in securing the knee joint, preventing it from swaying too much sideways, controlling the knee's rotation, strengthening the posterior part of the joint capsule, and preventing overextension of the knee joint. On the other hand, inside the knee joint capsule, we find the intracapsular ligaments. The cruciate ligaments are the most well-known intracapsular ligaments. They prevent the femoral condyle from rolling backward and displacing during knee flexion or, oppositely, as a shield against the femoral condyle rolling forward and displacing during knee extension.

Muscles

Muscles, made of flexible fibers, are like elastic bands of the body. They contract (flex) to pull and move different parts of your body. Various muscles are in charge of controlling your knee movements.

We have two main types of muscles attached to the knee joint: flexors and extensors. Flexors pull your knee in, while extensors work in opposition to flexors, enabling you to extend your knee outward.

Nerves

Nerves send electrical signals between the brain and the rest of the body. In your knee, nerves such as the femoral, sciatic, tibial, and peroneal play a role in the communication network that enables you to sense things and control your muscles.