Muscles of the Thigh

Abstract

The thigh muscles can be split up into 3 major compartments; anterior, posterior and medial.
The anterior compartment contains the Sartorius, Pectineus, Iliopsoas and Quadriceps femoral muscles. This compartment is innervated by the femoral nerve and act to flex the hip or extend the knee.
The posterior compartment contains the Semitendinosus, Semimembranosus and Biceps femoris muscles. They are innervated by branches of the sciatic nerve and contribute to extension of the hip and flexion of the knee.
The medial compartment contains the Adductor muscles, Obturator externus and Gracilis muscles. These typically adduct the hip and are innervated by the obturator nerve.

Core

Introduction

The muscles of the thigh are responsible for a variety of movements, acting on both the hip and the knee joint. There are many muscles in the thigh, however, they can be categorised into the anterior, posterior and medial compartments.

These compartments are separated by layers of fascia.

It is also very important when studying muscles that you are comfortable with anatomical terminology, as a lot is used in these articles. For more information, please check out our Anatomical Terminology Article.

Diagram - The fascial compartments of the thigh. Pink represents the anterior compartment, green is the medial compartment and blue represents the posterior compartment

Public Domain Image [Public domain]

Anterior Compartment

The muscles of the anterior compartment of the thigh are innervated by the femoral nerve. Generally speaking, these muscles act to flex the leg at the hip joint and can also act on the knee joint.

Diagram - Muscles of the anterior thigh. Note that the vastus intermedialis tucked underneath the rectus femoris and is, therefore, not visible

Creative commons source by OpenStax College [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Sartorius

This muscle is the longest in the body and runs in an oblique fashion across the anterior thigh. It is long, thin and is the most superficial of the anterior compartment muscles. It runs from the anterior superior iliac spine and runs inferomedially to the medial tibia.

It flexes, abducts and laterally rotates the hip joint and flexes the knee joint.

Pectineus

This is a flat muscle that runs from the anterior surface of the pubis to the pectineal line of the femur. It’s placement within the body allows it to flex and adduct the hip joint.

Vastus Muscles

There are three vastus muscles that contribute the quadriceps femoris group of muscles. These muscles are responsible for extension of the knee joint. They all attach to the patella via the patella tendon. There are three vastus muscles:

Vastus Lateralis – originating from the lateral lip of the linea aspera
Vastus Intermedialis – originating from the anterior surface of the femoral shaft
Vastus Medialis – originating from the medial lip of the linea aspera

Rectus Femoris

This muscle makes up the fourth muscle of quadriceps femoris. It originates from the ilium and attaches to the medial tibia. It flexes the hip and extends the knee.

Iliopsoas

This muscle is a combination of both the psoas major and iliacus muscles, hence the name.

They contribute to flexion of the hip joint.

Posterior Compartment

Thankfully, the posterior compartment is simpler. Collectively, these muscles are known as the hamstrings and are involved with extension of the hip and flexion of the knee. They are innervated by the sciatic nerve.

Diagram - Posterior compartment (Hamstring) muscles on the right leg highlighted in red

Creative commons source by OpenStax College, edited by Thomas Burnell [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Biceps Femoris

This muscle has two heads. The long head originates at the ischial tuberosity, whilst the short head originates at the linea aspera of the femur. Together, they insert into the head of the fibula. This tendon can be palpated on the lateral aspect of the posterior knee. The two heads are innervated by two different branches of the sciatic nerve: the long head by the tibial branch, and the short head by the common fibular branch. It can contribute to some lateral rotation of the hip and the knee, as well as extension of the hip and flexion of the knee.

Semitendinosus

This muscle lies medial to the biceps femoris. It originates from the ischial tuberosity and attaches to the medial tibia. It is primarily responsible for flexion of the knee joint and extension of the hip, but can also medially rotate the thigh. It is innervated by the tibial branch of the sciatic nerve. When looking at the back of the thigh, it can be difficult to differentiate between semintendinosus and semimembranosus - semitendinosus is the one with a very long tendon at the bottom that attaches to the medial tibia.

Semimembranosus

This is the most medial of the posterior muscles. It is deep to the semitendinosus muscle. Like the the other hamstrings, it originates from the ischial tuberosity. It attaches to the medial tibial condyle. In addition to extension of the hip and flexion of the knee, it can medially rotate the thigh. When looking at the back of the thigh, it can be difficult to differentiate between semintendinosus and semimembranosus - semimembranosus is the most medial of the hamstrings (both 'm' words).

Medial Compartment

These muscles are generally involved in hip adduction. They are innervated by the obturator nerve.

Diagram - Medial compartment of the thigh. Note that the Obturator Externus is not illustrated, but would be deep to pectineus and superior to adductor muscles

Creative commons source by Beth ohara, edited by Thomas Burnell [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Adductor Muscles

These are a group of muscles found in the medial thigh. They are primarily responsible for hip adduction and originate from the pubis. There are three muscles in this group:

Adductor brevis – a short muscle that lies beneath adductor longus. It attaches to the linea aspera on the posterior femur.
Adductor longus – a long, fan-shaped muscle that spans the length of the linea aspera.
Adductor magnus – the largest muscle in the medial compartment. It is also the most deep of all the medial compartment muscles. This muscle can be divided into two regions, an adductor region and a hamstring region. The adductor region offers hip flexion whilst the hamstring region contributes to hip extension.

Obturator Externus

Obturator Externus is the most superior of the medial compartment muscles. It attaches to greater trochanter, and originates from the membrane covering the obturator foramen (the big hole in the pelvis made by the ischium and pubis). In addition to adduction, it also contributes to lateral rotation of the thigh.

Gracilis

The most superficial and most medial of the muscles in the medial compartment. It originates from the pubis and descends to the medial surface of the tibia. It, therefore, also contributes to flexion of the knee in addition to hip adduction.

For Pathologies and Conditions affecting the Thigh area, check out our Conditions of the Thigh article.

Edited by: Dr. Marcus Judge and Dr. Maddie Swannack

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