Knee Joint Anatomy

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

Knee joint anatomy involves looking at each of the different structures in and around the knee.

The knee joint is the largest and one of the most complex joints in the human body.

There are various muscles that control movement, ligaments that give stability, special cartilage to absorb pressure and various other structures to ensure smooth, pain-free movement.

Knee pain is a common problem that affects people at all ages. Many different things can go wrong with the knee. Understanding the anatomy of the knee and how the different parts fit together and function normally is the first step to understanding your knee problem and fixing it.

• Knee Bones
• Cartilage & Meniscus
• Leg & Knee Muscles
• Ligaments
• Tendons
• Bursa
• Joint Capsule
• Knee Cap

We start by looking at the features of each element of knee joint anatomy and then we will go on to look at the common problems that can develop with each of the different components of the anatomy of the knee.

There are four knee bones that fit together to make two different knee joints:

• Femur: the thigh bone
• Patella: the kneecap
• Tibia: the main shin bone
• Fibula: the outer shin bone

The knee bones work together to support the entire body and transfer forces between the hip and foot, allowing the leg to move smoothly and efficiently. 

Human knee joint anatomy actually comprises of two joints, the

• Tibiofemoral Joint: the main knee joint between the thigh and shin bones
• Patellofemoral Joint: the joint between the kneecap and thigh bone 

You can find out all about the different bones and joints that make up the knee, how they function and what can go wrong in the knee bone anatomy section.

• Articular Cartilage: a thin layer of cartilage which lines the surfaces of the knee joints
• Knee Meniscus: a special extra thick layer of cartilage that sits on the top of the tibia

The knee meniscus is particularly important as it acts as a shock absorber to reduce the forces going through the bones and reduces friction, allowing the bones to move smoothly. 

The back of the patella is also lined with cartilage, the thickest in the whole body due to the immense forces that go through the kneecap.

You can find out all about the different types of knee cartilage, how they work, and cartilage injuries and how to treat them in the knee joint cartilage anatomy section.

When looking at knee and leg muscle anatomy, the main knee muscles controlling the leg are the: 

• Quadriceps: four muscles on the front of the thigh which straighten the knee - rectus femoris, vastus medialis, vastus lateralis and vastus intermedius
  
  
• Hamstrings: three muscles on the back of the thigh which bend the knee - semimembranosus, semitendinosus and biceps femoris
  
  
• Glutes: three buttock muscles, very important in controlling the position of the knee and how the forces transfer through the joint - gluteus maximus, gluteus medius and gluteus minimus
  
  
• Calves: two muscles on the back of the lower leg that control both the knee and ankle - gastrocnemius and soleus

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 knee joint, reducing pain and swelling, and improving function.

You can find out all about the different muscles in knee joint anatomy, how they work, how they can get damaged and how to strengthen and stretch them in the knee and leg muscle anatomy section.

When thinking about knee joint anatomy in terms of stability, it is the knee ligaments that are  most important as they are the main stabilising structures of the knee preventing excessive movements and instability. Ligaments are tough, fibrous connective tissues which link bone to bone, made of collagen.

There are two sets of knee ligaments:

• Cruciate Ligaments: anterior and posterior, ACL & PCL which sit inside the middle of the joint controlling forwards, backwards and twisting motion at the knee
• Collateral ligaments: medial and lateral, MCL & LCL that are found either side of the joint and control sideways stability of the knee

In the knee ligament anatomy section we look at each of the different ligament in-depth including how they work, what their role is, how they get damaged and how to make the best recovery from ligament injuries.

Now let's have a look at knee bursa anatomy. There are approximately fourteen bursa around the knee. 

Bursa are small fluid filled sacs that reduce the friction between the bones and soft tissues to prevent inflammation.

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

In the knee bursa anatomy section we look at each of the bursa, where they are, what they do, how they get injured and how to make a full recover from bursitis.

When looking at the anterior aspect of knee joint anatomy, you will find the patella (kneecap). The patella is a small, triangular bone which sits in the quadriceps muscle at the front of the knee.

The kneecap is lined with cartilage which is actually the thickest cartilage in the whole body due to the massive forces that go through it e.g. the force going through the kneecap when coming downstairs is 3.5x body weight. 

Knee cap pain is one of the most common problems associated with the knee.