What is the Difference Between Psoas and Hip Flexor

The main difference between psoas and hip flexor is that psoas is one of the biggest and strongest muscles in the hip flexor, whereas the hip flexor is a group of muscles occurring in the front of the upper thigh.

Psoas and hip flexor are two muscles that occur in the upper thigh. The hip flexor is the muscle that helps in flexing the hip. 

Key Areas Covered

1. What is Psoas
– Definition, Structure, Function
2. What is Hip Flexor
– Definition, Structure, Function
3. Similarities – Psoas and Hip Flexor
– Outline of Common Features
4. Difference Between Psoas and Hip Flexor
– Comparison of Key Differences

Key Terms 

Hip Flexor, Psoas

What is Psoas

Psoas is one of the significant muscles that occur on either side of the vertebral column. It combines with the iliacus muscle at the distal end, forming the iliopsoas muscle. It contains a deep, superficial segment. The deeper segment of the psoas muscle originates from the first four lumbar vertebrae. The superficial segment of the psoas originates from the lateral surface of the distal thoracic vertebrae. Moreover, lumber flexus occurs between the deep and the superficial layers. A common tendon attaches the iliopsoas muscle to the lesser trochanter of the femur. 

Figure 1: Psoas

Furthermore, the contraction of the psoas muscle leads to external rotation and abduction of the femur. It changes the orientation of the upper portion of the muscle changes from the superior-inferior direction to a horizontal direction. The anterior, middle portion of the muscle reaches the pubic branch passing the inguinal ligament. 

What is Hip Flexor 

The hip flexor muscle is the muscle responsible for flexing the hip that brings the knee closer to the chest. There are five key muscles in the hip flexor: iliac, psoas, pectineus, rectus femoris, and sartorius. The shape of the iliacus muscle is like a triangle. It is flat and an exact fit of the iliac fossa. The Iliac fossa is a curved surface of the pelvic bone. Along with the psoas muscle, it forms the iliopsoas muscle. Two third of the top of the iliopsoas muscle attaches to the iliac fossa. Psoas is a muscle that overlies the vertebral column. It is a long fusiform muscle located on either side of the vertebral column.

Figure 2: Anterior Hip Muscles

Moreover, pectineus occurs in the medial compartment of the anterior and the middle part of the upper thigh. It adducts the thigh, moving the leg toward the middle of the body. The rectus femoris is responsible for flexing the hip along with the iliopsoas and sartorius. Additionally, sartorius is the longest muscle in the human body. It is a thin, long, superficial muscle running down the length of the thigh. 

Similarities Between Psoas and Hip Flexor

• Psoas and hip flexor are two muscles that occur in the upper thigh.
• They are responsible for the flexing of the thigh.

Difference Between Psoas and Hip Flexor

Definition

Psoas refers to each of a pair of large muscles which run from the lumbar spine on either side and, with the iliacus, flex the hip, while hip flexor refers to a muscle that functions in flexing the hip, i.e., bringing the knee closer to the chest.

Location

Psoas locates in the lumbar region of the spine, while the hip flexor locates in the front top part of the thigh. 

Anatomy

Moreover, psoas is a long muscle that occurs on either side of the vertebral column and the brim of the lesser pelvis, while the hip flexor consists of five key muscles: iliacus, psoas, pectineus, rectus femoris, and sartorius.  

Significance

Psoas is one of the biggest and strongest muscles that occur in the hip flexor, while the hip flexor is a group of muscles occurring in the front of the upper thigh.

Function

Psoas is the major contributor to the flexion of the hip joint, while the hip flexor is responsible for the hip flexion. 

Conclusion

In brief, the psoas and hip flexor are two muscles in the upper thigh. They are responsible for flexing the hip. Psoas is one of the largest and strong muscles of the hip flexor. It locates in the lumbar region of the spine. It is a long muscle that occurs on either side of the vertebral column. Importantly, it is the major contributor to flexion. In comparison, the hip flexor is the group of muscles responsible for hip flexion. It occurs in the front part of the thigh. It comprises five key muscles, including iliacus, psoas, pectineus, rectus femoris, and sartorius. Therefore, the main difference between psoas and hip flexors is their anatomy and function.

References:

1. Siccardi MA, Tariq MA, Valle C. Anatomy, Bony Pelvis and Lower Limb: Psoas Major. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.
2. Hip flexors. Physiopedia. (n.d.-b). 

Image Courtesy:

1. “Gray430-en” By Jmarchn – Own work (CC-BY SA 3.0) via Commons Wikimedia
2. “Anterior Hip Muscles 2” By Beth ohara – Own Work (CC-BY SA 3.0) via Commons Wikimedia