Knee Joint Anatomy

Understanding knee joint anatomy helps us to know what can go wrong with the knee. The knee joint is the largest and one of the most complex joints in body.

Knee pain is a common problem that affects people at all ages.  So many different things can go wrong with the knee, and if we understand how everything should work, we can make sure we do the right things to ensure a full recovery, prevent injuries and stop problems coming back.

When looking at knee joint anatomy, the human knee actually comprises of two joints, the tibiofemoral joint (thigh and shin bones) and patellofemoral joint (kneecap). It is a hinge joint which means it can bend, straighten and twist.

The knee is a synovial joint which means it has a joint capsule which is like a sac surrounding the joint. The capsule contains synovial fluid which nourishes and lubricates the joint allowing it to move smoothly and painlessly - a bit like the oil in your car.

The Different Parts of the Knee

Here we will look at the different structures that make up the knee joint, how they work and how they fit together - click on the links to find out more about each structure.  When thinking about knee joint anatomy, we should consider the:

1) Knee Bones

There are 4 bones that make up the joint: the tibia (shin bone), femur (thigh bone), patella (kneecap) and fibula (on the outer side of the shin). They support the body and transfer forces between the hip and foot, allowing the leg to move smoothly and efficiently.

2) Meniscus & Cartilage

A really important part of knee joint anatomy is the cartilage.  There are 2 types of cartilage in the knee: articular cartilage, which lines the joint, and the meniscus which is a special extra layer of thick cartilage. These acts as shock absorbers to reduce the forces going through the bones, and reduce friction, allowing the bones to move smoothly. 

Meniscus tears are commonly associated with twisting knee injuries and arthritis and can cause pain, locking (knee gets stuck) and swelling.

3) Muscles

The main muscles controlling the leg are the quadriceps, 4 muscles on the front of the thigh which straighten the knee, and the hamstrings, the muscles on the back of the thigh which bend the knee. The glutes (buttock muscles) are also very important in controlling the position of the knee and how the forces transfer through the joint.

Weakness and tightness in the leg muscles are common causes of knee pain.  By stretching and strengthening the knee muscles, you can reduce the forces going through the joint, reducing pain and swelling, and improving function.

4) Ligaments

These are tough, fibrous connective tissues which link bone to bone, made of collagen. In knee joint anatomy, they are the main stabilising structures of the knee (ACL, PCL, MCL, LCL) preventing excessive movements and instability.

The most common ligament injuries are ACL tears, MCL tears and knee sprains which occur when the ligaments are overstretched. 

4) Tendons

These are soft tissues which link muscle to bone eg the patellar tendon. They are frequently damaged by overuse or excessive stretching resulting in tendonitis.  The most common knee tendonitis problem is patellar tendonitis (aka Jumpers Knee) at the front of the knee.

6) Joint Capsule

This is like a bag that surrounds the joint containing synovial fluid to nourish and lubricate the knee allowing it to move smoothly and freely. 

7) Bursa

These are small fluid filled sacs that reduce the friction between the bones and soft tissues to prevent inflammation. There are approximately 14 bursa around the knee. 

If there is excessive friction on the bursa, usually due to muscle weakness or tightness, the bursa gets inflammed, known as knee bursitis.

8) Kneecap

When looking at the anterior aspect of knee joint anatomy, you will find the patella (kneecap). This is a small, triangular bone which sits in the quadriceps muscle at the front of the knee. The patella is lined with cartilage which is actually the thickest cartilage in the whole body due to the massive forces that go through it eg the force going through the kneecap when coming downstairs is 3.5x bodyweight.  Knee cap pain is one of the most common problems associated with the knee.

To learn more about the different elements in knee joint anatomy, use the links above.

Functions of the Knee

The specific design of knee joint anatomy allows a number of functions:

1) Supports body in upright position without muscles having to work
2) Helps in lowering and raising body eg sitting, climbing and squatting
3) Allows rotation/twisting of the leg to place and position foot accurately
4) Makes walking more efficient - just try walking without bending your knees and you'll see how much harder it is
5) Acts with the ankle joint as a strong forward propeller of the body - particularly important when running
6) Provides stability and proprioception of the leg
7) Acts as a shock absorber

Lots of things can go wrong in the knee joint, causing pain. To find out more, check out the sections on knee injuries and common problems.

Find Out More

Find out more indepth information about knee joint anatomy by choosing from the following links: muscles, bones, cartilage/meniscus, ligaments and bursa.

If you have a knee problem and want help working out what is wrong, visit the diagnosis section.

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Updated 30th April 2013
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