Knee Anatomy: Complete Guide to Parts, Names & Diagram

Overview of Knee Anatomy

Your knees are crucial joints, connecting your thigh with your leg. The knee anatomy consists of a tibiofemoral joint & patellofemoral joint: one joins your thigh bone (femur) with your shinbone (tibia), and the other connects your thigh bone with the kneecap (patella). These joints allow various activities like walking, running, and jumping. In addition to bones, the knee’s anatomy contains muscles, cartilage, ligaments, and nerves. They allow your legs to bend and flex, making a wide range of movements possible.
The knee has several crucial functions. It moves your legs, provides stability, helps you keep your balance, and supports your body when standing or moving. Without strong and healthy knees, everyday tasks would be much more challenging.

Knee Anatomy Diagram

Parts of the Knee

Bones

Femur (Thigh bone)
Tibia (Shin Bone)
Patella (Kneecap)

Joints

Patellofemoral joint
Tibiofemoral joint
Tibiofibular joint
- Superior Tibiofibular Joint
- Inferior Tibiofibular Joint
- Interosseous Membrane

Muscles

Flexion Muscles (Hamstring)
- Biceps femoris
- Semitendinosus
- Semimembranosus
Extension Muscles
- Rectus femoris
- Vastus lateralis
- Vastus medialis
- Vastus intermedius

Innervation

Femoral nerve
Tibial nerve
Common fibular nerves
Posterior division of the obturator nerve

Ligaments

Anterior Cruciate Ligament (ACL)
Posterior Cruciate Ligament (PCL)
Medial Collateral Ligament (MCL)
Lateral Collateral Ligament (LCL)

Cartilage

Hyaline Cartilage
Fibrocartilage
Articular Cartilage

Knee Anatomy – Bones

Femur (Thigh bone)

The femur, or thigh bone, is your body’s longest and strongest bone. It helps you stand, walk, and move around by supporting your weight and working with muscles, tendons, and ligaments.

The top part of the femur connects to a special socket in the pelvis called the hip joint. At the bottom of the femur, it joins with the shinbone (tibia) and the kneecap (patella) to create the knee joint.

Surgery may be needed to fix it if it breaks, usually from a big impact like a fall or car crash. Afterward, physical therapy can help you regain strength and movement.

Tibia (Shin Bone)

The tibia, or shinbone, is a key bone in the lower leg. It is located at the front and closer to the body’s midline. It works with the fibula and is linked by a tough membrane that allows limited movement.

The main function of the tibia is to connect the knee joint to the ankle. It is the second-largest bone in the body after the femur. This strong bone is crucial for weight bearing because of its sturdy structure.

Patella (Kneecap)

The patella, also known as the kneecap, is like a shield for your knee joint. It is a flat, triangular bone in front of your knee. It is a protective cover for the part where your thigh and lower leg bones meet.

Many animals, like mice, cats, birds, and dogs, also have a patella. But whales and most reptiles don’t have patella.

The patella is a special bone in humans because it starts as soft cartilage when we are born. But as we grow, it turns into hard bone.

The patella is a triangle with its point facing down. That pointy part is called the apex, and it connects to the patellar ligament, which helps hold everything together around your knee.

Knee Anatomy – Joint

Patellofemoral Joint

Your patellofemoral joint is where your kneecap and thigh bone meet at the front of your knee. The femur has a groove where the patella sits; both have smooth, cartilage-covered surfaces.

The patella is a small, triangular bone attached to the thigh muscle via a tough tendon. This tendon continues below the patella, forming the patellar ligament, which connects to a groove on the shin bone.

This joint is important for activities like climbing, walking on inclines, and moving your knees. Everyday movements like walking up or down stairs, kneeling, or standing up from sitting engage this joint.

Tibiofemoral Joint

The tibiofemoral joint connects the lower end of the thigh bone to the top of the shinbone. It is like a hinge between the rounded ends of the thigh bone and the flat tops of the shinbone.

On the bottom of the thigh bone are two condyles, one on the inside and one on the outside. They are separated by a groove at the back. The inside one is bigger and more sticking out.

The top of the shinbone has two slightly curved parts that fit the thigh bone’s condyles, and a vertical ridge separates them.

Because the bone ends don’t fit perfectly, two cartilage wedges are in between to even out the pressure. They are called meniscus and act like cushions.

Tibiofibular Joint

The tibia and fibula, the two bones in the leg, connect at three key points: the superior tibiofibular joint, the inferior tibiofibular joint, and the interosseous membrane. These junctions work together to maintain stability while allowing limited movement for ankle flexibility.

Superior Tibiofibular Joint

This joint connects the upper ends of the tibia and fibula and is classified as a plane synovial joint. The tibial facet is on the lateral side of the top of the tibia, facing toward the back, down, and to the side.

The fibular facet sits on the head of the fibula, facing forward, up, and inward. These flat surfaces are coated with a slick layer of hyaline cartilage, letting them glide against each other.

Although this joint doesn’t facilitate active movements, it allows minor gliding motions to accommodate the ankle’s movement.

Inferior Tibiofibular Joint

This joint connects the lower ends of the tibia and fibula. It is a syndesmosis, a type of fibrous joint. Here, the fibula’s convex surface aligns with the tibia’s concave fibular notch.

This firm connection is critical for ankle stability but can stretch slightly to adapt to ankle movement.

Interosseous Membrane

This membrane links the shafts of the tibia and fibula along the length of the leg. It plays a crucial role in keeping the two bones together and helps distribute force between them.

Knee Muscle Anatomy – Flexion Muscles (Hamstring)

Biceps femoris

The Biceps Femoris is a muscle in the back of your thigh, part of the hamstring group. It helps bend your knees and extend your hips. It has two parts: the long and short heads, starting from the pelvis.

The long head goes around the back of your leg, crossing both the hip and knee joints, ending at the head of the fibula. The short head starts from the femur and joins the fibula head.

Its main jobs are bending the knee (bringing your heel toward your buttocks) and extending the hip (pushing your thigh backward).

This muscle is crucial for running and jumping, and it helps stabilize your knee during various movements.

Semitendinosus

The semimembranosus is a thigh muscle at the back of your leg, below another muscle called the semitendinosus. It helps you bend your knee, straighten your hip, and turn your thigh and knee inward.

It starts at a bone in your pelvis called the ischial tuberosity and goes down to the inner part of your shinbone. The deep femoral artery supplies it with blood, and it is controlled by the sciatic nerve, which helps you move.

This muscle teams up with others in your thigh to keep your knee steady when you run or jump. Strengthening these muscles is important to avoid injuries and improve at sports.

Semimembranosus

The semitendinosus is a muscle in the back of your thigh. It works alongside the biceps femoris and semimembranosus. It helps with bending your knee, straightening your hip, and rotating your thigh and shin. Also, it helps prevent over-bending at the hips.

This muscle starts from the bottom of your pelvis and connects to the inside of your shinbone. The tibial nerve and other muscles in the hamstring group control its actions.

Athletes often injure this muscle, especially during fast running or sudden movements.

Knee Muscle Anatomy – Extension Muscles

Rectus femoris

The rectus femoris is a key thigh muscle in the quadriceps group. It is special because it connects to both the hip and knee joints. This muscle is also known as the “kicking muscle” because it powers forceful knee extension, like in soccer kicks.

It starts at the front of the hip bone and goes down to the kneecap and shin bone. The femoral nerve controls it.

Vastus Lateralis

The vastus lateralis (VL) is a big muscle that helps straighten your knee. It is on the outer side of your thigh and connects your thigh bone to your kneecap.

The VL is extending your knee, helping you move, getting stronger, and keeping your hip and knee steady. It starts from your hip and thigh bones and goes down to your kneecap through the quadriceps tendon.

Vastus Medialis

The vastus medialis (VM) helps straighten the knee and stabilize the kneecap. It is part of a group of four muscles, the quadriceps femoris.

The VM has two parts: the upper part called the Vastus Medialis Longus (VML) and the lower part called the Vastus Medialis Obliquus (VMO), each playing a role in knee movement.

The VM receives nourishment for blood supply from the femoral artery, deep femoral artery, and a branch of the popliteal artery.

Nerve signals to the VM originate from lower femoral nerve roots and higher lumbar spinal segments, ensuring smooth coordination between the muscle and the central nervous system.

Knee Anatomy – Ligaments

Anterior Cruciate Ligament (ACL)

The ACL is a ligament in your knee that starts from the bottom of your leg bone (tibia), between and in front of intercondylar eminences.

It connects to the back inner side of the outer leg bone (femur), just behind the middle of the knee. This connection involves a mix of collagen fibers and solid bone through in-between tissue called fibrocartilage and mineralized fibrocartilage.

The ACL runs downward, inward, and a bit forward. It attaches to two spots on the outer side of the knee bone: one called the lateral intercondylar ridge and another called the lateral bifurcate ridge.

On the tibia, it hooks onto two medial and lateral intercondylar tubercles. These spots act as anchors for the anteromedial and posterolateral bundles.

Posterior Cruciate Ligament (PCL)

The posterior cruciate ligament in your knee runs along the back and connects your thigh to your lower leg bone. It helps keep your knee stable and allows for smooth movement.

It has two parts: the bigger anterolateral bundle (ALB) and the smaller posteromedial bundle (PMB). The ALB’s attachment on the thigh bone is about twice as big as its tibial attachment.

The PCL starts from the front and side of the medial femoral condyle and connects to the back of the tibial plateau, about a centimeter below the knee joint.

The research found that the PCL’s attachment areas on the femoral and tibial footprint are about three times bigger than the middle part of the ligament.

Medial Collateral Ligament (MCL)

The medial collateral ligament is a strong, flat band inside your knee that stretches from the medial epicondyle of the femur to the condyle of the tibia. It is a crucial part of the knee to prevent bending too much sideways.

When you hear about knee injuries in sports, the MCL often gets hurt. It is the most common type of knee ligament injury in activities like skiing, where there is much side-to-side movement.

The MCL has two main parts: the superficial ligament, also called the tibiofemoral ligament, and the deep ligament, known as the mid-third capsular ligament. These parts work together to keep your knee stable and safe during movement.

Lateral Collateral Ligament (LCL)

The fibular or lateral collateral ligament (LCL) is a strong cord in your knee that helps to keep it stable. It is one of four important ligaments that hold your knee joint steady.

The LCL mainly works on the outside of your knee, especially when pressure pushes your knee inward or your lower leg twists outward.

When your knee is straight, the LCL gets stretched out. It joins with the iliotibial band, adding to its strength. The popliteus tendon lies beneath the LCL, keeping it apart from the lateral meniscus. Plus, it splits the biceps femoris muscle into two parts.

As your knee bends, the LCL is less important for stability, especially past 30 degrees of bending. If the crucial ligaments in your knee are torn, the LCL steps in to help control your lower leg’s front and back movement.

Knee Anatomy: Complete Guide to Parts, Names, Functions & Diagram