The iliopsoas muscle (; ) refers to the joined

psoas major The psoas major ( or ; from ) 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 iliopsoas. In other animals, this muscle is e ...

and the

iliacus muscle The iliacus is a flat, triangular muscle which fills the iliac fossa. It forms the lateral portion of iliopsoas, providing flexion of the thigh and lower limb at the acetabulofemoral joint. Structure The iliacus arises from the iliac fossa on ...

s. The two muscles are separate in the

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

, but usually merge in the

thigh In 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 bone tissu ...

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

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

at the

lesser trochanter In human anatomy, the lesser trochanter is a conical, posteromedial, bony projection from the shaft of the femur. It serves as the principal insertion site of the iliopsoas muscle. Structure The lesser trochanter is a conical posteromedial p ...

. It acts as the strongest

flexor In anatomy, flexor is a muscle that contracts to perform flexion (from the Latin verb ''flectere'', to bend), a movement that decreases the angle between the bones converging at a joint. For example, one's elbow joint flexes when one brin ...

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. It is the largest branch of the lumbar plexus. Structure The femoral nerve is the major nerve supplying the ant ...

(iliacus).

Structure

The iliopsoas muscle is a

composite muscle Composite or hybrid muscles are those muscles which have more than one set of fibers but perform the same function and are usually supplied by different nerves for different set of fibers. Examples * Brachialis: Musculocutaneous nerve is motor a ...

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

vertebral bodies Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

of T12 and L1– L3 and their associated

intervertebral discs An intervertebral disc (British English), also spelled intervertebral disk (American English), lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the ver ...

. The iliacus originates in the

iliac fossa The iliac fossa is a large, smooth, concave surface on the internal surface of the Ilium (bone), 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 ...

of the

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

. 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 The psoas minor muscle ( or ; from ) is a long, slender skeletal muscle. When present, it is located anterior to the psoas major muscle.Tank (2005), p 93Gray (2008), p 1372 Structure The psoas minor muscle originates from the vertical fascicles ...

does contribute to the iliopsoas muscle. The inferior portion below the inguinal ligament forms part of the floor of the

femoral triangle The femoral triangle (or Scarpa's triangle) is an anatomical region of the upper third of the thigh. It is a subfascial space which appears as a triangular depression below the inguinal ligament when the thigh is flexed, abducted and laterally r ...

Nerve supply

The psoas major is innervated by direct branches of the anterior rami of the

lumbar plexus The lumbar plexus is a web of nerves (a nerve plexus) in the lumbar region of the body which forms part of the larger lumbosacral plexus. It is formed by the divisions of the first four lumbar nerves (L1–L4) and from contributions of the su ...

at the levels of L1–L3, while the iliacus is innervated by the

(which is composed of nerves from the

anterior rami The ventral ramus (: rami) (Latin for 'branch') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami. Shortly after a spinal nerve e ...

of L2– L4).

Function

The iliopsoas is the prime mover of hip flexion, and is the strongest of the

hip flexors In anatomy, flexor is a muscle that contracts to perform flexion (from the Latin verb ''flectere'', to bend), a movement that decreases the angle between the bones converging at a joint. For example, one's elbow joint flexes when one brings the ...

(others are

rectus femoris The rectus femoris muscle is one of the four quadriceps muscles of the human body. The others are the vastus medialis, the vastus intermedius (deep to the rectus femoris), and the vastus lateralis. All four parts of the quadriceps muscle attach ...

, 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 and is continuous with the iliotibial band, which attaches to the tibia. The muscle as ...

). The iliopsoas is important for

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

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 as an " inverted pendulum" gait in which the body vaults o ...

, and

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

. The iliacus and psoas major perform different actions when postural changes occur. The iliopsoas muscle is covered by the

iliac fascia The iliac fascia (or Abernethy's fascia) is the fascia overlying the iliacus muscle. Superiorly and laterally, the iliac fascia is attached to the inner aspect of the iliac crest; inferiorly and laterally, it extends into the thigh to unite with ...

, 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. The purpose of the medial arcuate ligament is to attach ...

. Together with the

, it continues down to the

where it forms the

iliopectineal arch The iliopectineal arch is a thickened band of fused iliac fascia and psoas fascia passing from the posterior aspect of the inguinal ligament anteriorly across the front of the femoral nerve to attach to the iliopubic eminence of the hip bone pos ...

which separates the

muscular MUSCULAR (DS-200B), located in the United Kingdom, is the name of a surveillance program jointly operated by Britain's Government Communications Headquarters (GCHQ) and the U.S. National Security Agency (NSA) that was revealed by documents release ...

and

vascular lacuna The vascular lacuna (Latin: ''lacuna vasorum (retroinguinalis)'') is the medial compartment beneath the inguinal ligament. It is separated from the lateral muscular lacuna by the iliopectineal arch.Ross, L.M., Lamperti, E.D. (2006). Thieme: Atl ...

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. The j ...

, hip, groin, thigh, knee, or any combination. The iliopsoas gets innervation from the L2-4 nerve roots of the

which also send branches to the superficial lumbar muscles. The

passes through the muscle and innervates the

quadriceps The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...

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 o ...

, 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 ilia ...

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 or 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 ...

adductor longus In the human body, the adductor longus is a skeletal muscle located in the thigh. One of the adductor muscles of the hip, its main function is to Adduction, adduct the thigh and it is innervated by the obturator nerve. It forms the medial wall ...

adductor brevis The adductor brevis is a muscle in the thigh situated immediately deep to the pectineus and adductor longus. It belongs to the adductor muscle group. The main function of the adductor brevis is to pull the thigh medially. The adductor brevi ...

adductor magnus The adductor magnus is a large triangular muscle, situated on the medial side of the thigh. It consists of two parts. The portion which arises from the ischiopubic ramus (a small part of the inferior ramus of the pubis, and the inferior ramu ...

, 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, urethr ...

in patients who are undergoing blood

anticoagulation An anticoagulant, commonly known as a blood thinner, is a chemical substance that prevents or reduces the coagulation of blood, prolonging the clotting time. Some occur naturally in blood-eating animals, such as leeches and mosquitoes, which h ...

Additional images

File:Slide20LLLL.JPG, Iliopsoas muscle File:Gerrish's Text-book of Anatomy (1902) - Fig. 346.png, Origin and attachment of the M. psoas major. File:Gerrish's Text-book of Anatomy (1902) - Fig. 347.png, Origin and attachment of the M. iliacus. File:Braus 1921 244.png

References

External links

* {{Authority control Hip flexors Iliopsoas muscles Muscles of the lower limb