Knee Anatomy

Listen To Dr. Matthew Lawless Explain The Different Structures Of The Knee

The knee is made up of three bones – the thigh bone, or femur; the shin bone, or tibia; and the knee cap, or patella. There is a fourth bone, the fibula, that helps with knee function but sits just below the knee on the outside (lateral side).

The bones are held together by four ligaments. The one on the inside of the knee is called the medial collateral ligament (MCL). The one on the outside is called the lateral collateral ligament (LCL). There are two ligaments that cross (cruciate) in the middle of your knee. The one that runs from the front, or anterior, aspect of your tibia to the back, or posterior, aspect of the femur is called the anterior cruciate ligament (ACL). The fourth one, called the posterior cruciate ligament (PCL), runs from the anterior aspect of the femur to the posterior aspect of tibia.

There are other less known and not quite as big ligaments, most notably the one that helps stabilize the patella in the middle of the knee, which is called the medial patella femoral ligament (MPFL).

The ends of the bones are covered with a layers of smooth cartilage called hylan cartilage.

The knee is one big cavity surrounded by tissue called synovium. The job of the synovium is to produce a small amount of lubricating fluid, called synovial fluid, to allow the femur to glide smoothly on the tibia.

There are two load-sharing pieces of cartilage that cushion between the femur and tibia – one that sits on the medial side (the medial meniscus) and the one that sits on the lateral side (the lateral meniscus).  Both meniscus are anchored to the flatter-shaped tibia to allow the curved femur to slide on top.

The knee functions and moves by the action of muscles. The main muscle sets that connect around the knee are the quadriceps and the hamstrings. The quadriceps are made up of four muscles on the front of the femur that act in concert to extend (straighten) the knee. The muscles originate on the top part of the thigh and hip and converge to form the quadriceps tendon just above the patella. At the patella, the quadriceps tendon becomes the patellar tendon and inserts onto the front of the tibia.  The muscles on the back of the thigh are called the hamstrings. These three muscles also begin at top of the thigh and hip (on the back side) and end on the tibia and fibula.  These hamstring muscles function to bend the knee.

When healthy and functioning normally, these muscles act to bend and straighten the knee in a smooth and efficient way. Unfortunately, many things can go wrong with each of the structures of the knee.

Anterior/Front View

Here is a picture showing the muscles on the front of the knee.

The quadriceps muscles (vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris) all converge on the quadriceps tendon just above the knee cap, or patella.  

At the patella, the quadriceps tendon continues, becoming the patellar tendon (called the patellar ligament in this picture) where it inserts onto your tibia.

The quadriceps muscles act to extend or straighten your knee.

Posterior/Back View

Here is a picture showing the muscles on the back of your leg that act to bend, or flex, your knee. 

They are called the hamstring muscles, and travel down the back of your thigh and insert into the tibia and fibular head.

There are three hamstring muscles: the semimembranous, semitendonosis, and the biceps femoris. 

Internal View

This is a picture of your medial and lateral meniscus.  

The medial menicus sits on the inside of your knee while the lateral meniscus sits on the outside.  

Since this picture is taken from the top down with the femur removed you can see how the ACL, PCL, MCL and LCL are also situated. 

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