Muscles of the Anterior Thigh

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Introduction

The thigh is the part of the leg that runs between the hip and the knee. It consists of three muscular compartments: anterior, posterior, and medial (Figure 1). This article will focus on the anterior compartment of the thigh.

The muscles that make up the anterior compartment of the thigh are sartorius and the quadriceps femoris muscles (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius). Psoas major and iliacus muscles also pass into the upper aspect of the anterior compartment.

The main action of this muscle group is to flex the thigh at the hip and extend the thigh at the knee. Innervation to this muscle group is the femoral nerve (L2, L3, L4). The blood supply is derived from the femoral artery.

Thigh compartments — **Figure 1**. Cross-section of the thigh showing the three main compartments.

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Iliopsoas

The iliopsoas is made up of the psoas major and iliacus muscles.

These both originate as separate muscles on the posterior abdominal wall. From their point of origin, they descend and pass laterally to the inguinal ligament into the upper aspect of the anterior compartment of the thigh, where they converge into a common tendon. This common tendon inserts onto the lesser trochanter of the femur.

Psoas major

Origin

Posterior abdominal wall: T12 to L5

Insertion

Lesser trochanter of the femur

Innervation

Anterior rami of L1, L2 and L3

Action

Flexion of the hip

Iliacus

Origin

Posterior abdominal wall: in the iliac fossa

Insertion

Lesser trochanter of the femur

Innervation

Femoral nerve (L2, L3)

Action

Flexion of the hip

Quadriceps femoris

Quadriceps femoris is a muscle group comprised of four individual muscles which make up the bulk of the anterior compartment of the thigh.

These muscles are rectus femoris, vastus medialis, vastus intermedius and vastus lateralis. This muscle group works to extend the leg at the knee, as well as stabilising the patella during knee movement.

Rectus femoris

Origin

Rectus femoris has two heads of origin, one from the anterior inferior iliac spine (straight head) and the other from the ilium immediately superior to the acetabulum (reflected head)
The two heads converge to form a common muscle

Insertion

The rectus femoris tendon converges with the quadriceps femoris tendon to form the patellar tendon
The patellar tendon inserts onto the base of the patella

Innervation

Femoral nerve (L2, L3, L4)

Action

Flexion of the hip
Extension of the knee

Vastus medialis

Vastus medialis is the most medial muscle in the quadriceps femoris group, hence its name. It sits lateral to sartorius and medial to rectus femoris.

Origin

The vastus medialis has a long origin along the femur.
It starts on the intertrochanteric line, descends posteroinferiorly along the pectinate line and along the linea aspera, down to the medial supracondylar line.

Insertion

It inserts onto the medial aspect of the quadriceps tendon and the medial border of the patella.

Innervation

Femoral nerve (L2, L3, L4)

Action

Extension of the knee

Vastus intermedius

Vastus intermedius gets its name as it is the middle of the three vastus muscles. It lies behind rectus femoris and medial to the vastus lateralis muscle.

Origin

The muscle originates from the upper two-thirds of the anterolateral surface of the femur.

Insertion

Vastus intermedius inserts onto the quadriceps femoris tendon, as well as the lateral border of the patella and the lateral condyle of the tibia.

Innervation

Femoral nerve (L2, L3, L4)

Action

Extension of the knee

Vastus lateralis

Vastus lateralis is the largest of the quadriceps femoris muscle group. As its name suggests, it is the most lateral muscle in the vastus group and lies on the outside of the thigh.

Origin

The muscle originates along the femur, starting from the superior intertrochanteric line, before moving laterally to the lateral gluteal tuberosity and down the lateral aspect of the linea aspera.

Insertion

Vastus lateralis inserts onto the quadriceps femoris tendon and the lateral aspect of the patella.

Innervation

Femoral nerve (L2, L3, L4)

Action

Extension of the knee

Sartorius

Sartorius is the most superficial muscle of the anterior compartment and runs obliquely from the anterior superior iliac spine on the pelvis (lateral) to the tibia (medial). It is not part of the quadriceps femoris group as it does not have an insertion onto the common quadriceps tendon.

In the upper third of the thigh, the medial border of sartorius forms the lateral wall of the femoral triangle.

Origin

Originates on the anterior superior iliac spine (ASIS) on the pelvis

Insertion

Inserts onto the medial aspect of the tibia, just inferior to the tibial tuberosity

Innervation

Femoral nerve (L2, L3)

Action

Flexion of the hip
Flexion of the knee
Abduction of the thigh
Lateral rotation of the thigh

Clinical relevance: compartment syndrome¹

Compartment syndrome occurs when there is a build-up of pressure inside a fascial compartment in a limb.

Pressure in the compartment builds and eventually compresses veins and nerves, reducing blood flow away from the muscles and sensation. When pressure is above diastolic blood pressure, arteries will also become compressed. Causes of compartment syndrome include limb trauma, haemorrhage and compression (e.g. a plaster cast).

The main symptom of compartment syndrome is pain out-of-keeping with physical examination findings. Due to nerve compression, numbness or paraesthesia may also occur. Passive stretching of the muscles in the affected compartment will exacerbate the pain.

Acute compartment syndrome is a surgical emergency and must be treated quickly to avoid tissue necrosis. The only treatment is to relieve the pressure within the fascial compartment by performing a fasciotomy. This involves making an incision into the skin to open the compartment and relieve the pressure. Sometimes these incisions are left open for several days to allow the pressure to subside completely.

Summary table

Table 1. The muscles of the anterior thigh.

Muscle	Origin	Insertion	Innervation	Function
Psoas major	Posterior abdominal wall	Lesser trochanter of the femur	Anterior rami of L2-L4	Flexion of the hip
Iliacus	Posterior abdominal wall	Lesser trochanter of the femur	Femoral nerve (L2, L3)	Flexion of the hip
Rectus femoris	Straight head: ASIS Reflected head: ilium, just superior to acetabulum	Quadriceps femoris tendon	Femoral nerve (L2-L4)	Flexion of the hip Extension of the knee
Vastus medialis	From intertrochanteric line, descends posteroinferiorly along the pectinate line and along the linea aspera, down to the medial supracondylar line.	Quadriceps femoris tendon Medial border of patella	Femoral nerve (L2-L4)	Extension of the knee
Vastus intermedius	Upper two-thirds of the anterolateral surface of the femur	Quadriceps femoris tendon Lateral border of patella Lateral tibial condyle	Femoral nerve (L2-L4)	Extension of the knee
Vastus lateralis	The superior intertrochanteric line, before moving laterally to the lateral gluteal tuberosity and down the lateral aspect of the linea aspera.	Quadriceps femoris tendon Lateral border of the patella	Femoral nerve (L2-L4)	Extension of the knee
Sartorius	Anterior superior iliac spine	Medial surface of tibia, just below tibial tuberosity	Femoral nerve (L2, L3)	Flexion of the hip Flexion of the knee

Editor

Dr Chris Jefferies

References

OrthoInfo. Compartment Syndrome. Published October 2009. Available from: [LINK]
Richard L. Drake, A. Wayne Vogyl, Adam W.M. Mitchell. Gray’s Anatomy for Students 3^rd Anterior compartment of the thigh, Lower Limb. Pages 589-953. Elsevier. Published in 2015.