Muscles in the Anterior Compartment of the Thigh

Original Author: Oliver Jones
Last Updated: February 16, 2017
Revisions: 29

The musculature of the thigh can be split into three sections; anterior, medial and posterior. Each compartment has a distinct innervation and function.

The muscles in the anterior compartment of the thigh are innervated by the femoral nerve (L2-L4), and as a general rule, act to extend the leg at the knee joint.

There are three major muscles in the anterior thigh – the pectineus, sartorius and quadriceps femoris. In addition to these, the end of the iliopsoas muscle passes into the anterior compartment.

This article will cover the attachments, actions, innervations and clinical correlations of these muscles.


Iliopsoas

Fig 1.0 - The muscles of the anterior thigh.

Fig 1.0 – The muscles of the anterior thigh.

The iliopsoas is actually two muscles, the psoas major and the iliacus. They originate in different areas, but come together to form a tendon, hence why they are commonly referred to as one muscle.

Unlike many of the anterior thigh muscles, the iliopsoas does not extend the leg at the knee joint.

  • Attachments: The psoas major originates from the lumbar vertebrae, and the iliacus originates from the iliac fossa of the pelvis. They insert together onto the lesser trochanter of the femur.
  • Actions: The iliopsoas flexes the lower limb at the hip joint and assists in lateral rotation at the hip joint.
  • Innervation: The psoas major is innervated by anterior rami of L1-3, while the iliacus is innervated by the femoral nerve.

Quadriceps Femoris

The quadriceps femoris consists of four individual muscles; three vastus muscles and the rectus femoris. They form the main bulk of the thigh, and collectively are one of the most powerful muscles in the body.

The muscles that form quadriceps femoris unite proximal to the knee, and distally attach to the patella via the patella tendon. The patella attaches to the tibia by the patella ligament. The quadriceps femoris is the main extensor of the knee.

Vastus Lateralis

  • Proximal attachment: Originates from the greater trochanter and the lateral lip of linea aspera.
  • Actions: Extends the knee joint and stabilises the patella.
  • Innervation: Femoral nerve.

Vastus intermedius

  • Proximal attachment: Anterior and lateral surfaces of the femoral shaft.
  • Actions: Extends the knee joint and stabilises the patella.
  • Innervation: Femoral nerve.

Vastus medialis

  • Proximal attachment: The intertrochanteric line and medial lip of the linea aspera.
  • Actions: Extends the knee joint and stabilises the patella, particularly due to its horizontal fibres at the distal end.
  • Innervation: Femoral nerve.

Rectus Femoris

  • Attachments: Originates from the ilium, just superior to the acetabulum.  It runs straight down the leg (the Latin for straight is rectus), and attaches to the patella by the quadriceps femoris tendon.
  • Actions: This is the only muscle of the quadriceps to cross both the hip and knee joints. It flexes the leg at the hip joint, and extends at the knee joint.
  • Innervation: Femoral nerve.

Sartorius

The sartorius is the longest muscle in the body. It is long and thin, running across the thigh in a inferomedial direction. The sartorius is positioned more superficially than the other muscles in the leg.

  • Attachments: Originates from the anterior superior iliac spine, and attaches to the superior, medial surface of the tibia.
  • Actions: At the hip joint, it is a flexor, abductor and lateral rotator. At the knee joint, it is also a flexor.
  • Innervation: Femoral nerve.
Fig 1.1 - Cross section of the distal thigh. The iliopsoas and pectineus muscles originate and attach in the proximal thigh, and hence are not included in this diagram.

Fig 1.1 – Cross section of the distal thigh. The iliopsoas and pectineus muscles originate and attach in the proximal thigh, and hence are not included in this diagram.


Pectineus

The pectineus muscle is a flat muscle that forms the base of the femoral triangle. It has a dual innervation, and thus can be considered a transitional muscle between the anterior thigh and medial thigh compartments.

  • Attachments: It originates from the pectineal line on the anterior surface of the pelvis, and attaches to the pectineal line on the posterior side of the femur, just inferior to the lesser trochanter.
  • Actions: Adduction and flexion at the hip joint.
  • Innervation: Femoral nerve. May also receive a branch from the obturator nerve.

Clinical Relevance: Testing the Quadriceps Femoris

The quadriceps femoris muscle can be used to test the femoral nerve in cases of suspected nerve palsy.

This is performed by positioning the patient supine, with the knee slightly flexed. The patient is asked to extend the leg (at the knee) against resistance. If the femoral nerve is damaged, contraction of the quadriceps femoris will be absent.

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Question 1 / 4
Which muscle of the quadriceps crosses both the hip and the knee joint?

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Question 2 / 4
What is the innervation of psoas major?

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Question 3 / 4
Which of the following best describes the function of sartorius at the hip?

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Question 4 / 4
Damage to which of these nerve roots would affect the function of the femoral nerve?

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