Iliacus is a triangular muscle of the iliac region which together with the psoas major, comprises the iliopsoas muscle. The iliacus muscle belongs the group of the inner hip muscles, together with the psoas major, psoas minor, obturator externus, obturator internus, superior gemellus, inferior gemellus, piriformis, and quadratus femoris muscles.
As a group, the inner hip muscles act upon the hip joint. The function of the iliacus muscle in particular is described together with that of the psoas major, i.e. from the aspect of the iliopsoas muscle. Having said that, the iliopsoas is the chief flexor of the hip joint. It also contributes to the lateral flexion of the trunk. However, the latter movement is produced by the psoas major muscle only, without any involvement of the iliacus muscle.
This article will discuss the anatomy and function of the iliacus muscle.
|Lesser trochanter of femur
|Hip joint: Thigh/trunk flexion
|Femoral nerve (L1-L3)
|Iliolumbar, deep circumflex iliac, obturator, and femoral arterie
- Origin and insertion
- Blood supply
- Clinical relations
Origin and insertion
The iliacus muscle has a vast origin, the majority of it arising from the superior two-thirds of the iliac fossa. The rest arises from several other origin points, which are the inner lip of the iliac crest, the lateral aspect of the sacrum and anterior sacroiliac and iliolumbar ligaments. The muscle fibers converge distally towards the hip, thus contributing to the triangular shape of this muscle.
At the level of the capsule of the hip joint, the iliacus muscle fibers blend with those of the psoas major muscle, forming a common tendon for the iliopsoas. The tendon of iliopsoas crosses the anterior surface of the hip joint to finally insert to the lesser trochanter of femur. Before insertion, the tendon of iliopsoas receives a small slip called the iliocapsularis muscle, which is a small muscle lying just superficial to the hip joint capsule.
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The anterior surface of the pelvic part of the iliacus muscle is covered with the iliac fascia, which separates it from the peritoneum. This surface of the iliacus is also crossed by the lateral femoral cutaneous nerve, the cecum on the right side, and the iliac part of the descending colon on the left side. The medial margin of the iliacus muscle is in relation with the femoral nerve and lateral margin of the psoas major muscle.
The anterior surface of the thigh portion of the iliacus muscle lies posterior to the fascia lata, rectus femoris and sartorius muscles. It is also crossed by the deep femoral artery (profunda femoris). The posterior surface of the iliacus is adjacent to the hip joint, from which it is separated by a large subtendinous iliac bursa.
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The iliacus muscle is innervated by the femoral nerve (L2-L4).
The iliacus muscle works in synergy with the psoas major muscle to produce movements in the hip joint. When its proximal attachment is fixed, the muscle contributes to the flexion of the thigh. On the other hand, with its distal attachment fixed, the muscle helps to bring the trunk forwards against resistance. These actions are essential for lower limb functions such as walking, running and jumping.
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Shortening of the iliacus muscle
The iliacus muscle is prone to shorten in people who have a desk job or exercise heavily without stretching. The shortening of iliacus muscle results in its dysfunction and consequential hindering of the hip joint movements.
This kind of injury to iliacus manifests with the following symptoms:
- Pain of the iliacus muscle which is the most intense on the so called trigger points, which are the tight or stiff points of the muscle
- Decreased range of motion on the hip joint and impaired gait
The most common treatment is physical therapy which promotes stretching of the iliacus muscle.
Iliacus muscle: want to learn more about it?
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