The iliopsoas muscle (; from lat, ile, lit=groin and grc, ψόᾱ, psóā, muscles of the loins) refers to the joined

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 ilio ...

and the iliacus muscles. The two muscles are separate in the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...

, but usually merge in 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 ...

. They are usually given the common name ''iliopsoas''. The iliopsoas muscle joins to 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 ...

at 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 ...

. It acts as the strongest flexor of the hip. The iliopsoas muscle is supplied by the lumbar spinal nerves L1– L3 (psoas) and parts of 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 ...

(iliacus).

Structure

The iliopsoas muscle is a composite muscle formed from the psoas major muscle, and the iliacus muscle. The psoas major originates along the outer surfaces of the

vertebral bodies The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

of T12 and L1– L3 and their associated intervertebral discs. The iliacus originates in the iliac fossa of the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

. The psoas major unites with the iliacus at the level of the

inguinal ligament The inguinal ligament (), also known as Poupart's ligament or groin ligament, is a band running from the pubic tubercle to the anterior superior iliac spine. It forms the base of the inguinal canal through which an indirect inguinal hernia may ...

. It crosses the hip joint to insert on the

of the

. The iliopsoas is classified as an "anterior hip muscle" or "inner hip muscle". The psoas minor does contribute to the iliopsoas muscle. The inferior portion below the inguinal ligament forms part of the floor of the femoral triangle.

Nerve supply

The psoas major is innervated by direct branches of the anterior rami of the lumbar plexus at the levels of L1–L3, while the iliacus is innervated by the

(which is composed of nerves from the anterior rami of L2– L4).

Function

The iliopsoas is the prime mover of hip flexion, and is the strongest of the hip flexors (others are rectus femoris, sartorius, and

tensor fasciae latae The tensor fasciae latae (or tensor fasciæ latæ or, formerly, tensor vaginae femoris) is a muscle of the thigh. Together with the gluteus maximus, it acts on the iliotibial band and is continuous with the iliotibial tract, which attaches to the ...

). The iliopsoas is important for

standing Standing, also referred to as orthostasis, is a position in which the body is held in an ''erect'' ("orthostatic") position and supported only by the feet. Although seemingly static, the body rocks slightly back and forth from the ankle in the s ...

walking Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an ' inverted pendulum' gait in which the body vaults ...

, and

running Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot. Running is a type of gait characterized by an aerial phase in which all feet are above the ground (though there are exceptions). This i ...

. The iliacus and psoas major perform different actions when postural changes occur. The iliopsoas muscle is covered by the iliac fascia, which begins as a strong tube-shaped psoas fascia, which surround the psoas major muscle as it passes under the

medial arcuate ligament The medial arcuate ligament (also medial lumbocostal arch and internal arcuate ligament) is a tendinous fascia that arches over the psoas major muscle as it passes posterior the diaphragm. Structure The medial arcuate ligament is an arch in the f ...

. Together with the iliac fascia, it continues down to the

where it forms the iliopectineal arch which separates the muscular and vascular lacunae.

Clinical significance

It is a typical posture muscle dominated by slow-twitch red type 1 fibers. Since it originates from the lumbar vertebrae and discs and then inserts onto the femur, any structure from the lumbar spine to the femur can be affected directly. A short and tight iliopsoas often presents as externally rotated legs and feet. It can cause pain in the low or mid back,

SI 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. T ...

, hip, groin, thigh, knee, or any combination. The iliopsoas gets innervation from the L2-4 nerve roots of the lumbar plexus which also send branches to the superficial lumbar muscles. The

passes through the muscle and innervates the quadriceps,

pectineus The pectineus muscle (, from the Latin word ''pecten'', meaning comb) is a flat, quadrangular muscle, situated at the anterior (front) part of the upper and medial (inner) aspect of the thigh. The pectineus muscle is the most anterior adductor ...

, and

sartorius muscle The sartorius muscle () is the longest muscle in the human body. It is a long, thin, superficial muscle that runs down the length of the thigh in the anterior compartment. Structure The sartorius muscle originates from the anterior superior ili ...

s. It also comprises the intermediate femoral cutaneous and medial femoral cutaneous nerves which are responsible for sensation over the anterior and medial aspects of the thigh, medial shin, and arch of the foot nerves. The

obturator nerve The obturator nerve in human anatomy arises from the ventral divisions of the second, third, and fourth lumbar nerves in the lumbar plexus; the branch from the third is the largest, while that from the second is often very small. Structure The o ...

also passes through the muscle which is responsible for the sensory innervation of the skin of the medial aspect of the thigh and motor innervation of the adductor muscles of the lower extremity (

external obturator The external obturator muscle, obturator externus muscle (; OE) is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis. It is sometimes considered part of the medial compartment of thigh, and sometimes c ...

, adductor longus, adductor brevis,

adductor magnus Adductor may refer to: * One of the anatomical terms of motion 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 terminolo ...

, gracilis) and sometimes the

. Any of these innervated structures can be affected.

Bleeding

Iliopsoas muscle is a common site of

bleeding Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...

in patients who are undergoing blood

anticoagulation Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where the ...

Structure

Nerve supply

Function

Clinical significance

Bleeding

Additional images

See also

References

External links