Muscles involved in knee motion


The muscles which are responsible for knee movement as they relate to the thigh all originate along the pelvic girdle or the thigh. The fascia lata and the iliotibital tract each yield continuations known as fascial sheets. These fascial sheets surround and even segregate these muscles into specific compartments. Their division is useful in determining both function and position as they are divided into either the anterior extensors or the posterior flexors.



The anterior muscles are the extensor muscles. Crossing over the anterior aspect of the thigh, the elongated sartorius muscles resembles a strap and is useful to both the hip joint and the knee joint. Flexion and lateral rotation of the hip can occur just as easily as flexion and medial rotation of the knee. Nick named the “tailor’s muscle” it is the longest muscle of the human body. The anterior muscles share a common insertion point along the patella and are attached via the patellar tendon.

The patellar tendon runs continuously over the patella and then branches directly into the patellar ligament. The patellar ligament attaches to the tibial tuberosity. The satorius and the quadriceps femoris work in complete unison with each other in order to perform functions. Excellent examples of their unique abilities include the actions of kicking a football and similar moves that work the knee against the thigh.

The quadriceps femoris includes 4 muscles. The rectus femoris is the only one out of the 4 muscles which can affect either the hip joint or the knee joint, despite its superficial location.


Muscles involved in knee motion
Image: Muscles Involved In Knee Motion

The largest muscle of the quadriceps femoris group is the vastus lateralis. As the name implies, this muscle runs laterally. For medicinal injections in infants, this muscle is a common site for injections when the buttocks or the shoulder muscles aren’t available or acceptable sites.

The medial muscle of the thigh in this group is the vastus medialis. The vastus intermedius can be found deep to the rectus femoris, and is the mid sized version of the other two vastus muscles.


The posterior muscles are also referred to as the flexor muscles. The 3 posterior muscles of the thigh are counter acting muscles known as antagonistic muscles of the quadriceps femoris. This arrangement allows for knee flexion. The muscles of flexion are often referred to as the hamstring muscles. This common term was developed from butchering practicing of swine, as butchers relied on this same tendon to hang hocks of pork to dry.

The posterior lateral aspect of the thigh is devoted to the biceps femoris. This muscle initiates movement of either the hip or the knee and is equipped with two different heads; one superficial and long and one that is short and much deeper.

The posterior medial aspect of the thigh is devoted to the semi-tendonous fusiform muscle. This muscle is also capable of performing active functions on either the hip or the knee.

Along the posterior aspect of the thigh, there is an additional flattened semi membranous muscle that can be found positioned deep in comparison to the semitendonous muscle.
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