Knee Anatomy

Bones

The knee is composed of four bones that make up three separate joints, which work together to allow movement through various positions in dance.

These four bones are the Femur (thigh bone), Tibia (shin bone), Patella (knee cap), and fibula.

Joints

The femur and tibia articulate to form the tibiofemoral joint, which is the main “hinge” joint of the knee.

The patella and femur create the patellofemoral joint. The patella sits in a groove along the front of the femur, and glides through the groove as the knee bends and straightens. If the patella does not glide smoothly in this groove on the femur for various reasons, pain and injury can result (see below).

The tibia and fibula make two joints, one at the outside of the knee (the proximal tibiofibular joint), and one at the ankle (the distal tibiofibular joint). These joints connect the motions of the knee and ankle, and the fibula slides forward and backward as the knee bends and straightens.

Muscles

The quadriceps are the muscles on the front of the thigh. This muscle group is composed of the vastus lateralis (outside), vastus medialis (inside), vastus intermedius (underneath), and rectus femoris (on top). All four parts connect into one tendon that encases the patella. This tendon continues below the patella to connect to the tibia. These muscles extend, or straighten, the knee.

The hamstrings are the muscles on the back of the thigh. This muscle group is composed of the biceps femoris (outside), the semimembranosus, and the semitendinosus (inside). All three begin at one common tendon attached to the ischial tuberosity of the pelvis (sit bones). The semimembranosus and semitendinosus connect to the tibia on the inside of the leg, and the biceps femoris connects to the top of the fibula on the outside of the leg. These muscles flex, or bend, the knee.

The popliteus is a muscle that runs diagonally across the back of the knee, underneath the hamstrings, from the lateral femur to the medial tibia. Its function is to “unlock” the knee by providing slight rotation at the knee as it moves between flexion and extension.

The gastrocnemius is one of the calf muscles, but attaches to the femur at the back of the knee, and runs down to attach to the calcaneus (heel bone) through the achilles tendon. It acts as a secondary knee flexor.

Iliotibial Band

The iliotibial band, often referred to as the “IT Band” is a long band of fascia that begins at the hip, and runs down along the outside of the thigh to attach to the tibia below the knee. It also acts as a stabilizer for the lateral (outside) aspect of the knee. When the IT Band becomes excessively tight, knee pain and injury may occur (see below).

Ligaments

Cruciate Ligaments:

These ligaments act as knee stabilizers and restrict how much the tibia and femur can slide on each other. They create a cross or an “X” deep inside the knee, and are named for where they attach on the tibia. The Anterior Cruciate Ligament (ACL) runs from the front of the tibia to the back of the femur, and the Posterior Cruciate Ligament  (PCL) runs from the back of the tibia to the front of the femur.

Collateral Ligaments:

The collateral ligaments run along the inside and outside of the knee from the femur to the tibia. These ligaments stabilize the knee and protect it from sideways forces. The Medial Collateral Ligament (MCL) runs from the inside of the tibia to the inside of the femur, and the Lateral Collateral Ligament (LCL) runs from the outside of the femur to the top of the fibula.

Menisci

The menisci (plural of meniscus) are fibrocartilage rings that sit on top of the tibia, and stabilize the knee as well as act to cushion the knee from the forces placed upon it and through it while dancing. The medial meniscus is “C” shaped, and solidly attached to the tibia, while the lateral meniscus is “O” shaped, and is slightly more mobile.

Resources

 Author unknown. Knee Pain Health Center. Last updated 2012. Available at http://www.webmd.com/pain-management/knee-pain/picture-of-the-knee. Accessed December 17, 2012.

 Author unknown. Medical Look: Your Medical World. Last updated 2012. Available at http://www.medicalook.com/human_anatomy/organs/Muscles_involved_in_knee_motion.html. Accessed December 17, 2012.

 Author unknown. Nucleus Medical Media. Last updated 2007. Available at http://pages.uoregon.edu/esorens1/hphy362.pbwiki.com/Knee+Musculature.html Accessed December 17, 2012.

Author unknown. Achieve Therapy and Fitness. Last updated 2011. Available at http://www.achieve-therapy.com/Injuries-Conditions/Knee/Surgery/Meniscal-Surgery/a~353/article.html. Accessed December 17, 2012.

Author unknown. Medchrome: Medical and Health Articles. The Anatomy of Knee Joint. Last updated 2012. Available at  http://medchrome.com/basic-science/anatomy/the-knee-joint/. Accessed December 17, 2012.