Knee Anatomy

Knee pain is a common issue that can worsen and interfere with your everyday activities, especially when accompanied by swelling, tenderness, or inflammation. It’s important to seek medical advice in these cases.

At Complete Orthopedics, we specialize in managing pain following knee replacement surgery with personalized treatment plans and surgical options. We focus on thoroughly understanding your symptoms, providing accurate diagnoses, and applying the most effective methods to alleviate pain after surgery or consider further surgical procedures.

Our clinics, located throughout New York City and Long Island, are associated with six leading hospitals and equipped with the latest technology for advanced knee surgeries and outstanding orthopedic care. Scheduling an appointment with our orthopedic surgeons is simple and can be done online or by phone.

Learn about the various causes of knee pain and the treatment options available, including when additional surgery might be necessary.


The knee joint is made up of four bones. The femur or thighbone is the bone connecting the hip to the knee. The tibia or shinbone connects the knee to the ankle. The patella (kneecap) is the small bone in front of the knee and rides on the knee joint as the knee bends. The fibula is a thinner bone running parallel to the tibia on its outside. The knee joint acts like a hinge but with some degrees of rotation also.

The knee is a synovial joint, which means that the capsule is lined by synovium. The synovium produces fluid lubricating and nourishing the inside of the joint. Articular cartilage is the smooth surfaces at the end of the femur and tibia. It is the damage to this surface which causes arthritis.

X-ray showing knee anatomy.

X-ray showing knee anatomy.


Bones of the Knee

The knee joint is formed by three main bones:

Femur (Thighbone): The longest bone in the body, the femur extends from the hip to the knee. Its lower end has two rounded projections called condyles, which articulate with the tibia.

Tibia (Shinbone): The larger of the two lower leg bones, the tibia supports most of the body’s weight. Its upper end is broad and flat, forming the tibial plateau that interacts with the femur.

Patella (Kneecap): A small, triangular bone located in front of the knee joint. It protects the joint and enhances the leverage of the quadriceps muscle.


Ligaments of the Knee

Ligaments are tough, fibrous tissues that connect bones to each other. The knee has four primary ligaments:

Anterior Cruciate Ligament (ACL): Located in the center of the knee, the ACL prevents the tibia from sliding out in front of the femur and provides rotational stability.

Posterior Cruciate Ligament (PCL): Positioned behind the ACL, the PCL prevents the tibia from sliding backward under the femur.

Medial Collateral Ligament (MCL): Found on the inner side of the knee, the MCL provides stability against valgus forces (inward bending of the knee).

Lateral Collateral Ligament (LCL): Located on the outer side of the knee, the LCL provides stability against varus forces (outward bending of the knee).


Tendons and Muscles

Tendons connect muscles to bones. The major tendons and muscles involved in knee function include:

Quadriceps Tendon: Connects the quadriceps muscle to the patella.

Patellar Tendon: Connects the patella to the tibia.

Hamstrings: A group of muscles at the back of the thigh that help bend the knee.

Quadriceps: The large muscle group at the front of the thigh that straightens the knee.



The knee contains two crescent-shaped pieces of cartilage called menisci:

Medial Meniscus: Located on the inner side of the knee.

Lateral Meniscus: Located on the outer side of the knee.

The menisci act as shock absorbers, reducing the impact on the knee joint during activities like walking and running.


Joint Capsule and Synovial Membrane

The knee joint is enclosed in a capsule that provides support and stability. The inner lining of the capsule, called the synovial membrane, produces synovial fluid, which lubricates the joint and reduces friction.



Bursae are small fluid-filled sacs that cushion the knee and reduce friction between its components. There are several bursae around the knee, including:

Prepatellar Bursa: Located in front of the patella.

Infrapatellar Bursa: Found below the patella.

Pes Anserine Bursa: Located on the inner side of the knee.


Biomechanics of the Knee

The knee’s biomechanics involve the movement and interaction of its components during various activities. Key aspects include:

Flexion and Extension: The knee primarily moves in a hinge-like manner, bending (flexion) and straightening (extension).

Rotation: While the primary movement is hinge-like, the knee also allows a small amount of rotation, especially when it is bent.

Load Distribution: The menisci and cartilage help distribute the load across the knee joint, minimizing stress on any single component.


Common Knee Injuries

Understanding knee anatomy is crucial for diagnosing and treating knee injuries. Some common knee injuries include:

ACL Tears: Often caused by sudden stops or changes in direction, common in sports like soccer and basketball.

Meniscal Tears: Can result from twisting motions or direct impact, often seen in athletes and older adults.

Patellar Tendinitis: Also known as “jumper’s knee,” caused by overuse and repetitive stress on the patellar tendon.


Prevention and Care

Maintaining knee health involves several strategies:

Strengthening Exercises: Building strength in the quadriceps, hamstrings, and calf muscles can help support the knee joint.

Stretching: Regular stretching improves flexibility and reduces the risk of injury.

Proper Footwear: Wearing shoes that provide good support and cushioning can help protect the knees.

Avoiding Overuse: Gradually increasing activity levels and taking rest days can prevent overuse injuries.



The knee is a complex joint that plays a vital role in mobility and weight-bearing activities. Its intricate anatomy, including bones, ligaments, tendons, muscles, and other structures, works together to provide stability and movement. Understanding the knee’s anatomy and biomechanics is essential for preventing injuries and maintaining overall knee health. Whether you’re an athlete or someone looking to stay active, taking care of your knees is crucial for a healthy, active lifestyle.



Do you have more questions? 

What are the main functions of the knee joint?

The knee joint allows for movement (flexion and extension), supports body weight, and provides stability during activities like walking, running, and jumping.

How does the ACL prevent knee injuries?

The ACL prevents the tibia from sliding forward and provides rotational stability, which is crucial during activities involving sudden stops or changes in direction.

What role do the menisci play in the knee joint?

The menisci act as shock absorbers, distribute weight evenly across the knee, and provide stability by improving the fit between the femur and tibia.

How do the quadriceps muscles contribute to knee function?

The quadriceps muscles straighten the knee (extension) and stabilize the patella, enhancing the knee’s ability to bear weight and perform activities.

What is the significance of the patellar tendon?

The patellar tendon connects the patella to the tibia, transmitting the force from the quadriceps muscles to straighten the knee.

How can one prevent common knee injuries?

Prevent injuries by strengthening muscles around the knee, maintaining flexibility, wearing proper footwear, and avoiding excessive stress on the knee joint.

What is the role of the synovial fluid in the knee?

Synovial fluid lubricates the knee joint, reducing friction and allowing smooth movement between the joint surfaces.

How does the PCL differ from the ACL?

The PCL prevents the tibia from sliding backward and provides stability in the posterior direction, while the ACL prevents forward sliding and rotational instability.

What causes patellar tendinitis, and how is it treated?

Patellar tendinitis, or “jumper’s knee,” is caused by overuse and repetitive stress. Treatment includes rest, ice, physical therapy, and sometimes anti-inflammatory medications.

Why are bursae important in the knee joint?

Bursae reduce friction and cushion the knee, preventing irritation and inflammation of the surrounding tissues during movement.

What types of exercises are beneficial for knee health?

Strengthening exercises for the quadriceps, hamstrings, and calf muscles, as well as flexibility and balance exercises, are beneficial for knee health.

How does cartilage contribute to knee function?

Cartilage covers the ends of bones in the knee, providing a smooth, lubricated surface for joint movement and acting as a cushion to absorb impact.

What is the function of the MCL and LCL in knee stability?

The MCL provides stability against inward forces, while the LCL provides stability against outward forces, both crucial for maintaining knee alignment.

How do rotational movements affect the knee joint?

Rotational movements can stress the knee ligaments, particularly the ACL, increasing the risk of injury if the knee is not adequately stabilized.

What are common symptoms of a meniscal tear?

Symptoms include pain, swelling, stiffness, and a clicking or locking sensation in the knee.

How is an ACL tear diagnosed and treated?

An ACL tear is diagnosed through physical examination and imaging tests like MRI. Treatment may include rest, physical therapy, and surgery for severe cases.

What factors contribute to knee osteoarthritis?

Contributing factors include aging, joint injury, repetitive stress, obesity, and genetics.

How does knee anatomy differ between children and adults?

Children’s knee anatomy is still developing, with growth plates present in the bones, making them more susceptible to certain types of injuries compared to adults.

What is the recovery process for knee ligament injuries?

Recovery involves rest, physical therapy, and gradual return to activity. Severe injuries may require surgical repair and extensive rehabilitation.

How can proper footwear protect the knees?

Proper footwear provides support, cushioning, and stability, reducing the impact on the knees and preventing injuries.

What are the signs of a PCL injury?

Signs include pain, swelling, and instability in the knee, especially when bearing weight or walking downhill.

Why is knee flexibility important?

Flexibility allows for a full range of motion, reducing the risk of stiffness and injury, and ensuring proper function of the knee joint.

How do knee braces help in injury prevention and recovery?

Knee braces provide support, reduce stress on the knee, and limit movement to prevent further injury and aid in recovery.

What are the long-term effects of untreated knee injuries?

Untreated knee injuries can lead to chronic pain, instability, reduced mobility, and an increased risk of developing osteoarthritis.

How does weight affect knee health?

Excess weight puts additional stress on the knee joint, increasing the risk of injury and accelerating the wear and tear on cartilage and other structures.

I am Vedant Vaksha, Fellowship trained Spine, Sports and Arthroscopic Surgeon at Complete Orthopedics. I take care of patients with ailments of the neck, back, shoulder, knee, elbow and ankle. I personally approve this content and have written most of it myself.

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