The Human Knee Structure | Parts of the Knee and Their Functions

Human Knee Anatomy

The Human Knee structure  | Parts of the Knee and Their Functions

• Overview
• Parts of the Knee
• Function

Overview

The knee is the most complex joint in the body. It is a hinge joint that serves as a junction between the upper and lower leg.

Unlike the shoulder joint that has greater mobility thanks to the ball and socket structure, the human knee moves in a single plane of motion; bending backwards and extending forward.

This incredibly important joint is the largest one in the body with the ability to handle the body weight for the length of the day and also added weight when training (Especially on leg days).

A lot of muscles contribute to the movement of the knee, while ligaments provide stability throughout the motion, and other structures and fluids that ensure a smooth pain free movement. 

In addition, the cushion (Cartilage) inside the knee joint absorbs any moderate shocks that affect the knee, say, some falls or adding extra weight on a squat exercise.

The knee is a joint of a synovial type; i.e. it has a capsule around it secreting fluid to lubricate the joint in order for the flexion-extension plane of motion occurs with no pain experienced. 

Although the knee is a hinge joint, a small amount of rotation (Internal and external) is allowed by the structure.

Parts of the Knee

1. Bones

There are four bones that meet at the knee joint, namely the femur (Thigh bone) the tibia (Shin bone), the little flat triangular bone on top of the knee known as the patella (Knee cap) and lastly the fibula bone, which is on the outer side of the shin bone and  just next to the knee joint.

2. Cartilage

This is by far the most important part of the knee joint. Two types of cartilage are there to protect the knee against shocks and pain as long as they are in good condition. First of which, the articular cartilage is the layer of cartilage lining the end of both the femur and tibia (On the heads of these bones). 

The second cartilage is the meniscus; the shock absorber, which reduces friction, and takes pressure off the bones meeting at the knee joint. The meniscus sits at the top of the shin bone.

3. Ligaments

Ligaments are very essential to link bone to bone and provide stability and strength to the knee joint. 

These are highly required as little stability can be achieved by bones and cartilage alone. 

Four main ligaments are found to be making up the knee structure; they can be dived into two types.

Firstly, cruciate ligaments (ACL and PCL), that cross the middle of the joint. The ACL controls the forward motion of the tibia in relation to the femur. 

It also controls the twisting movement of the knee joint. The PCL, on the other hand, controls the backward motion of the tibia in relation to the femur. It also limits some rotation of the knee joint just like the ACL does.

Secondly, Collateral Ligaments (MCL and LCL) attach to both sides of the knee joint (Keeping the femur and tibia connected) and limits sideways motion of the knee joint.

4. Muscles

The muscles around the knee play a key role in stabilizing, aligning and moving the knee. Two main muscle groups do this job.

The quadriceps are a group of four distinct muscles that function to bring the knee from a flexed (Bent) position to an extended position by pulling the shin bone forward and fully straighten the leg.

The hamstrings are a group of three muscles that perform the opposite motion, that bringing the tibia backwards resulting in bending the knee.

5. Tendons

Tendons are the continuations of muscles that attach to the bones. 

They are made of collagen which makes them of a strong elastic nature. 

Tendons are associated with the same functions of the muscles (Flexion and extension).

The most important of all is the patellar tendon, which originates from the quadriceps and attaches to the tibia crossing the patella (The patella sits inside the patella tendon). This tendon is responsible for knee extension.

6. Bursa 

These are sacks filled with fluid distributed all around the knee. Their function is reduceing friction and smoothen the motion. 

There are around thirteen bursas around the knee, but the prepatellar bursa is the largest bursa that protects the patella. 

Direct trauma, excessive friction or pressure may affect the bursa resulting in knee

7. Articular Capsule

The knee capsule surrounds the knee joint and has two layers. 

The outer layer is a tough membrane which is made of ligament tissue; this holds the bones to the knee joint for stabilizing them. 

The inner layer, however, is a sonyval membrane that produces sonyval fluid. 

This fluid lubricates the knee joint, which makes it extremly essential for the smooth and pain-free movement. 

Function

The knee has plenty of functions that stabilize and facilitate movement of the whole body. 

Standing is one important function that the knee does with little help from muscles; so it stabilizes the leg and prevents it from collapsing. 

It also makes walking more efficient; I mean can you imagine walking with legs straight! 

The knee, along with the ankle, drives the leg in a forward motion to make walking or running possible. 

The knee absorbs a lot of shocks on a daily basis; shocks can come from walking down the stairs, walking up a hill, running, walking while carrying extra weight, having a  leg workout, and so on. 

Moreover, the knee joint helps the body lower or raise to fulfill daily needs (Sitting, standing, squatting, etc.) 

The little amount of rotation the knee joint can perform is also important to place the feet in an appropriate position for different purposes; whether an outward or forward pointing of the toes are needed, the knee joint can serve it.