The iliacus is a flat, triangular muscle which fills the

iliac fossa The iliac fossa is a large, smooth, concave surface on the internal surface of the ilium (part of the three fused bones making the hip bone). Structure The iliac fossa is bounded above by the iliac crest, and below by the arcuate line. It is b ...

. It forms the

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...

portion of

iliopsoas The iliopsoas muscle (; from lat, ile, lit=groin and grc, ψόᾱ, psóā, muscles of the loins) refers to the joined psoas major and the iliacus muscles. The two muscles are separate in the abdomen, but usually merge in the thigh. They are usu ...

, providing

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

of the

thigh In human anatomy, the thigh is the area between the hip ( pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of ...

and

lower limb The human leg, in the general word sense, is the entire lower limb of the human body, including the foot, thigh or sometimes even the hip or gluteal region. However, the definition in human anatomy refers only to the section of the lower limb ex ...

at the acetabulofemoral joint.

Structure

The iliacus arises from the

on the interior side of the

hip bone The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the ilium, isch ...

, and also from the region of the anterior inferior iliac spine (AIIS). It joins the

psoas major The psoas major ( or ; from grc, ψόᾱ, psóā, muscles of the loins) is a long fusiform muscle located in the lateral lumbar region between the vertebral column and the brim of the lesser pelvis. It joins the iliacus muscle to form the iliop ...

to form the

. It proceeds across the iliopubic eminence through the

muscular lacuna The muscular lacuna (Latin: ''lacuna musculorum'') is the lateral compartment of the thigh inferior to the inguinal ligament, for the passage of the iliopsoas muscle, the femoral nerve and the lateral cutaneous nerve of the thigh The lateral ...

to its insertion on the

lesser trochanter The lesser trochanter is a conical posteromedial bony projection of the femoral shaft. it serves as the principal insertion site of the iliopsoas muscle. Structure The lesser trochanter is a conical posteromedial projection of the shaft of the fe ...

of the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

. Its fibers are often inserted in front of those of the psoas major and extend distally over the lesser trochanter.Platzer (2004), p 234

Nerve supply

The iliopsoas is innervated by the

femoral nerve The femoral nerve is a nerve in the thigh that supplies skin on the upper thigh and inner leg, and the muscles that extend the knee. Structure The femoral nerve is the major nerve supplying the anterior compartment of the thigh. It is the largest ...

and direct branches from the

lumbar plexus The lumbar plexus is a web of nerves (a nervous plexus) in the lumbar region of the body which forms part of the larger lumbosacral plexus. It is formed by the Ventral ramus of spinal nerve, divisions of the first four lumbar nerves (L1-L4) and ...

.''Thieme Atlas of Anatomy'' (2006), p 422

Function

open-chain exercises Open chain exercises (OKC) are exercises that are performed where the hand or foot is free to move. The opposite of OKC are closed kinetic chain exercises (CKC). Both are effective for strengthening and rehabilitation objectives. Closed-chain exerc ...

, as part of the

, the iliacus is important for lifting (flexing) the femur forward (e.g.

front scale Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music *The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ea ...

). In

closed-chain exercises Closed kinetic chain exercises or closed chain exercises (CKC) are physical exercises performed where the hand (for arm movement) or foot The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a li ...

, the iliopsoas bends the trunk forward and can lift the trunk from a lying posture (e.g.

sit-ups The sit-up (or curl-up) is an abdominal endurance training exercise to strengthen, tighten and tone the abdominal muscles. It is similar to a crunch (crunches target the rectus abdominis and also work the external and internal obliques), but si ...

back scale The human back, also called the dorsum, is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck. It is the surface of the body opposite from the chest and the abdomen. The vertebral column runs ...

) because the psoas major crosses several vertebral joints and the

sacroiliac joint The sacroiliac joint or SI joint (SIJ) is the joint between the sacrum and the ilium bones of the pelvis, which are connected by strong ligaments. In humans, the sacrum supports the spine and is supported in turn by an ilium on each side. Th ...

. From its origin in the lesser pelvis the iliacus acts exclusively on the hip joint.

Additional images

File:Iliacus muscle - animation05.gif, Position of iliacus muscle (shown in red.) Animation. File:Gray236.png, Right

. Internal surface. (Iliac fossa visible at upper left.)

Notes

References

* *

External links

PTCentral
* - "Muscles and nerves of the posterior abdominal wall." * (, ) {{Authority control Hip flexors Hip muscles Iliopsoas muscles Muscles of the lower limb