# Knee Anatomy with Labels

A life\-size right knee in 3D, with labelled bones, ligaments and joints, showing how the ACL and PCL cross inside it as the knee bends\.

By Gina

Topic: Human Body & Medicine

[Open the interactive Jig](https://ask.jig.com/j/jBhP7eLnSY1E)

## Transcript

### 1. Meet the knee

This life\-size model shows a right knee from the front\. Four bones meet here: the thigh bone \(femur\), the shin bone \(tibia\), the thin fibula beside it and the kneecap \(patella\)\. Drag to turn the model\.

The patella is the largest bone in the body that grows inside a tendon\.

### 2. Three joints in one

The knee is really three joints working together\. The kneecap glides on the femur \(the patellofemoral joint\), and the femur's two rounded ends rock on the tibia in the lateral \(outer\) and medial \(inner\) tibiofemoral compartments\.

Smooth, slippery cartilage, shown in blue\-grey, coats every surface that touches\. Two rubbery pads called menisci cushion the tibia\.

### 3. A hinge that can twist

The knee is a modified hinge\. It bends \(flexion\) and straightens \(extension\), and while bent it can also twist a little inwards and outwards\. Watch the kneecap glide down over the end of the femur as the knee bends\.

A healthy knee bends to about 120 to 150 degrees\.

### 4. Ligaments at the front

Ligaments are tough bands that tie bone to bone\. The patellar ligament runs from the kneecap down to the tibia\. The medial collateral ligament \(MCL\) braces the inner side, and the lateral collateral ligament \(LCL\) the outer side\.

These three lie outside the joint capsule, so they are called extracapsular ligaments\.

### 5. Inside the front: the ACL

Bend the knee and fold the kneecap down, and the inside of the joint appears\. The anterior cruciate ligament \(ACL\) runs from the back of the femur to the front of the tibia and stops the shin sliding forwards\.

Cruciate means cross\-shaped: the ACL and the PCL cross like an X inside the joint\.

### 6. Ligaments at the back

Turn to the back of the knee\. The oblique popliteal ligament crosses the back wall on a slant, from the lower inner side up to the outer side\. The arcuate popliteal ligament arches up from the head of the fibula\.

Like the front ligaments, these two are extracapsular\.

### 7. The PCL

Lift away the back wall and the posterior cruciate ligament \(PCL\) appears\. It runs from the femur's notch down to the back of the tibia and stops the shin sliding backwards\. The ACL crosses in front of it\.

The PCL is tightest when the knee is bent; the ACL is tightest when it is nearly straight\.

### 8. The whole knee

Here is every labelled piece together\. Bend the knee with the slider, and drag to turn it around to find the ligaments at the back: each label stays with its part\.