Knee Anatomy

The Bones That Form the Knee Joint

Three primary bones form the knee, each contributing to stability and movement.

Femur (Thigh Bone)

The lower end of the femur has rounded surfaces that articulate with the tibia. Its shape influences how load transfers through the knee during walking, squatting, and turning.

Tibia (Shin Bone)

The top of the tibia forms a relatively flat platform called the tibial plateau. Subtle differences in tibial slope and alignment can affect ligament tension and weight distribution.

Patella (Kneecap)

The patella sits within the quadriceps tendon and tracks along a groove on the femur during bending and straightening. Its position helps improve the efficiency of knee extension.

Fibula (Outer Lower Leg Bone)

Although it does not directly form the knee joint, the fibula provides attachment points for important ligaments such as the lateral collateral ligament. It contributes to outer-side stability and plays a role in certain knee injuries.

Articular Cartilage and Smooth Joint Motion

Articular cartilage covers the ends of the femur and tibia, as well as the back of the patella. Its smooth surface allows low-friction movement and helps absorb load.

Changes in cartilage thickness or integrity may influence comfort during stairs, squatting, or longer periods of activity. Because cartilage does not have a strong blood supply, damage may not heal completely on its own.

The Menisci and Their Load-Sharing Role

The medial and lateral menisci sit between the femur and tibia. They help distribute force, improve stability, and support rotational control.

Medial Meniscus

Located on the inner side of the knee and firmly attached to surrounding structures, making it more susceptible to certain tears.

Lateral Meniscus

More mobile and shaped differently from the medial meniscus. It plays an important role in absorbing rotational forces.

Meniscal Attachments (Horns and Roots)

Each meniscus has front and back attachment points. These anchors help maintain shape and stability. Injuries affecting the meniscal roots may significantly alter how load is transmitted across the joint.

Cruciate and Collateral Ligaments

Several ligaments help guide knee movement and resist unwanted motion.

Anterior Cruciate Ligament (ACL)

It regulates forward and rotational motion of the tibia and contributes to stability during pivoting.

Posterior Cruciate Ligament (PCL)

Prevents backward shift of the tibia and contributes to stability during deep bending.

Medial Collateral Ligament (MCL)

Protects against inward forces and supports stability on the inner side of the knee.

Lateral Collateral Ligament (LCL)

Provides stability on the outer side and attaches near the fibular head.

Additional Ligament Structures That Guide Control

Beyond the major ligaments, the knee has secondary stabilisers that assist with fine-tuning movement.

Medial Patellofemoral Ligament (MPFL)

Helps keep the kneecap aligned, particularly during the first part of knee bending.

Anterolateral Ligament (ALL)

Supports rotational control and works together with the ACL to provide stability when turning or pivoting.

Posterolateral Corner (PLC) Structures

A group of ligaments and tendons at the outer back corner of the knee. These structures help control rotation, hyperextension, and side-to-side movement.

Tendons That Connect Muscle to Bone

Tendons transfer force from muscles to the knee bones, allowing movement.

Quadriceps Tendon

Connects the quadriceps muscle group to the top of the patella.

Patellar Tendon

Continues from the patella to the tibial tubercle, allowing the knee to straighten during walking, climbing, and standing.

Hamstring Tendons

Tendons from the semitendinosus and gracilis muscles attach to the inner side of the tibia. These play an important role in stability and are sometimes used in ligament reconstruction.

Iliotibial Band (ITB)

A thick band of connective tissue along the outer thigh attaches to the tibia. It influences rotational control and lateral knee stability.

The Bursa System and Soft-Tissue Cushioning

The knee contains multiple bursae, small fluid-filled sacs that minimise friction between surrounding tissues.

Prepatellar Bursa

Sits in front of the patella and may become irritated with prolonged kneeling.

Infrapatellar Bursa

Located below the patella, it helps cushion movement between the patellar tendon and the underlying bone.

Pes Anserine Bursa

Located on the inner side of the tibia, where several tendons insert. Irritation here may cause localised tenderness.

Suprapatellar Pouch

A larger recess above the patella where fluid can collect if the synovial lining becomes inflamed.

Joint Capsule and Synovial Lining

The knee joint is surrounded by a capsule made of strong connective tissue. Inside this capsule is the synovial lining, which produces joint fluid to lubricate the surfaces.

Inflammation of the synovial lining may lead to joint swelling, a feeling of fullness, or stiffness after rest. The capsule also contributes to stability, particularly at the extremes of motion.

Nerves and Blood Supply Around the Knee

Several nerves and blood vessels travel around the knee and support its function.

Saphenous Nerve

It supplies sensation to the inner side of the knee.

Common Fibular (Peroneal) Nerve

Wraps around the fibular head and supplies muscles involved in foot and ankle control.

Tibial Nerve

Runs deeper behind the knee and helps supply the lower leg.

Genicular Arteries

A vascular network delivers blood to the knee’s articular surfaces and supporting structures. Understanding these structures is important for explaining symptoms such as tingling, numbness, or discomfort in specific areas.

Alignment and Movement Axes

Knee function depends on how the bones align from the hip to the ankle.

Varus and Valgus Alignment

Refers to whether the knees angle slightly inward or outward. Alignment influences how load is shared across the joint.

Q-Angle

Describes the angle formed by the quadriceps pull on the patella. It affects patellofemoral tracking and may influence symptoms at the front of the knee.

Tibial Rotation and Femoral Version

Rotational differences in the thigh or shin bone can affect gait, patellar movement, and ligament forces.

How the Knee Moves: Basic Biomechanics

Knee biomechanics involve multiple structures working together to allow bending, straightening, rotation, and shock absorption.

Closed-Chain Movement

Occurs when the foot is on the ground, such as during walking, squatting, or climbing.

Open-Chain Movement

Occurs when the foot is free in the air, such as with leg extension exercises.

Shock Absorption and Force Transmission

The menisci, cartilage, and surrounding muscles absorb load each time the heel strikes the ground. Any change in these structures may alter how force travels across the knee.

How Knee Structures Work Together

The knee functions as an integrated system, and understanding the different knee structures can help explain how each element contributes to movement, stability, and load distribution.

• Bones provide the framework and alignment
• Cartilage and menisci allow smooth, cushioned motion
• Cruciate and collateral ligaments guide stability
• Patellofemoral stabilisers direct the kneecap
• Muscles and tendons supply power and dynamic control
• The capsule, synovium, bursae, nerves, and vessels support comfort and function

Changes in one area can influence several others. For example, swelling from cartilage irritation may reduce muscle activation, or a ligament injury may alter load through the menisci. Alignment differences can affect patellar tracking or ligament tension. This is why knee assessment considers all structures together.

When to Seek Review for Knee Symptoms

Although many symptoms settle with rest and activity modification, it may be helpful to seek assessment if you notice patterns that relate to the underlying structures of the knee.

You may consider review if you experience:

• Pain related to weight-bearing, bending, or twisting
• Swelling that recurs or persists after activity
• Clicking, catching, or locking that suggests mechanical irritation
• A feeling of instability or the knee giving way
• Difficulty with stairs, squatting, or returning to sport
• Stiffness that affects daily tasks or limits movement
• Uncertainty about imaging findings or how your knee anatomy relates to your symptoms

A knee specialist, such as Dr Jonathan Negus, or an orthopaedic knee surgeon in Sydney, can help determine which anatomical structures may be contributing to your symptoms and outline management options based on your examination and imaging.

Next Steps

If you would like help understanding your knee symptoms or anatomy, you can arrange a consultation with Dr Jonathan Negus to discuss your condition and treatment options.

If you are unsure which structures may be contributing to your symptoms, a personalised assessment can provide clarity and guidance.

This information is intended as a general guide and may not apply to every situation. Assessment and treatment recommendations vary depending on individual circumstances. Please speak with a qualified health professional for advice specific to your condition.