Knee Anatomy

The knee is a hinge joint that sits between the thigh and the shin.  It functions the same as a hinge on a door would and sometimes gets a creaky as a hinge can.  This joint allows the legs to bend and straighten which are necessary for walking, going up and down stairs, going from sitting to standing, running, and jumping. The anatomy of the knee consists of many structures from the bones, tendons and ligaments to the cartilage and muscles to help the knee function. 

If you want to learn more about the knee anatomy, please watch this knee anatomy video.

Bones and Joints

The knee consists of 3 main bones:                                         

  • the femur (thigh bone)
  • the tibia (shin bone)
  • the patella (knee cap)

The femur and the tibia are the main movers of the joint to allow for the hinge motion.  This connection of the femur and tibia is a joint called the tibiofemoral joint.   The patella sits on top of the tibiofemoral joint in a groove in the front of the femur.The patella is a floating bone that works as a fulcrum for the quadriceps muscle (you will read about this later) to function properly.  This joint is called the patellofemoral joint and allows for the patella to move up and down and the knee bends and straightens.  

Knee Anatomy and Ligaments

The knee has 4 main ligaments:

  • Medial collateral ligament (MCL) – is on the inside of the knee closer to the midline
  • Lateral collateral ligament (LCL) – is on the outside of the knee
  • Anterior cruciate ligament (ACL) – inside of the knee and crosses to the front
  • Posterior cruciate ligament (PCL) – inside of the knee and crosses to the back

The MCL and the LCL sit on the sides of the knee and they help give stability to the knee if your knee gets hit from the sides.  The ACL and PCL are inside of the knee and cross each other as they run front to back and vise versa.  These 2 ligaments are responsible for giving the knee stability from front to back.   An ACL injury is probably one of the most recognized injuries in sports and most of the time requires surgical repair that has a lengthy recover time.

Knee ligaments and anatomy.Knee Ligaments and Dislocation


There are two main types of cartilage in knee anatomy: articular cartilage and the meniscus. 

  • Articular cartilage covers the ends of the bones and allows for the bones to slide and glide on each other without friction.  This is the stuff you need to keep from getting the creaking and cracking of the joints.When this starts to wear down, arthritis will set in.
  • Meniscus – 2 thigh pieces of cartilage that sit on the tibia between the femur and tibia.These are C-shaped that allow for improved congruency of the joint.  Tears in these structures can cause pain, swelling, and sometime catching and locking of the knee joint.

Muscles of the Knee

There are many muscles that have an effect on the knee, but the main muscles that allow for the knee to perform its main functions are:

  • Quadriceps – a group of 4 muscles that sits on the front of the thigh.  These muscles are responsible for allowing the knee to straighten.  This movement is necessary for standing from a seated position, bringing your leg forward when walking, and kicking a ball!
  • Hamstrings – a group of 3 muscles that sits at the back of the thigh and allows for the knee to bend.  These muscles are responsible for lifting your foot to walk.
  • Gastrocs – a group of 2 muscles that sit in on the back side of the lower leg that work in tandem with the hamstrings to cause the knee to bend.  
  • Tendons attach the knee muscles to the bone.

All of these muscles also have functions at different joints such as the hip and the ankle.  Injuries to these structures, such as a pull or strain, will cause pain when activating the muscle and if severe enough will cause significant weakness.

There are many types of knee injuries that can occur.  Muscles, tendons, ligaments and cartilage can be strained and sprained. It is really important to have your knee pain properly diagnosed by an orthopedic physician.  JOI Rehab also has 12 Physical Therapy locations which can certainly help you on the road to recovery.  With over 70 Rehab Clinicians trained in providing you with the highest quality if orthopedic care. 

Even though this joint may seem like a simple joint, it can cause a lot of pain in many people.   Many injuries can occur from fractures to ligament/muscle/meniscal tears, and arthritis that can stop you in your tracks. Make sure you keep your knees mobile, keep stretching, and keep your legs strong to keep you moving!

If you want to learn more about a torn ACL, go to: Torn ACL

By Katie Trumble PT/ATC

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