Psoas Major Muscle Anatomy

Location & Overview

The psoas muscle is comprised of both the psoas major and the psoas minor (though the psoas minor muscle is sometimes absent in some individuals). The psoas major muscle is located in the lumbar region of the trunk. It is located laterally either side of the vertebral column. It also sits medially to the quadratus lumborum muscle and behind the psoas minor muscle. The psoas major and iliacus are both deep to the inguinal ligament, meaning they pass through the gap created between the inguinal ligament and the pelvis on their journey to their insertion point on the lesser trochanter of the femur. The distal end of the psoas major muscle combines together with the iliacus muscle to form a shared tendon as it connects to the lesser trochanter of the femur. The combining of these psoas muscles and the iliacus is referred to as the ‘iliopsoas muscle’, which is also sometimes also referred to as the ‘iliopsoas musculotendinous unit (IPMU)’. All these muscles work together as a strong flexor of the hip. The role of the hip flexors are to flex the hip joint, which involves lifting the upper leg towards the body^{[1] [2] [3] [4]}.

Origin & Insertion

The psoas major muscle originates on the transverse processes and the lateral surfaces of the bodies of the lumbar vertebrae L1 to L5. It also connects onto the vertebral bodies of T12 to L5. The vertebral origin also connects onto the intervertebral discs between these vertebrae. The psoas major then works its way down in an inferolateral direction passing underneath the inguinal ligament to insert onto the lesser trochanter of the femur^{[5] [6] [7]}.

Actions

The main action of the psoas major muscle is flexion of the hip joint. The psoas major can also provide weak assistance in external rotation (i.e. lateral rotation) of the femur in the hip joint. Another action the psoas major can perform is lateral flexion of the torso. However, it is again a weak role it plays in this movement comparative to other muscles such as the internal oblique and external oblique muscles. The psoas major also achieves this lateral flexion by only flexing one side at a time (unilateral contraction). It has also been suggested in the literature that the psoas major plays a dynamic stability role helping to keep the femur in place in the acetabulum during movement. ^{[8] [9] [10] [11] [12] [13] [14] [15]}.

Innervation

The psoas major muscle is innervated by the anterior rami of the first, second and third lumbar nerves (L1-L3) ^{[16] [17]}.

Blood Supply

Blood is supplied to the psoas major mainly via the lumbar branch of iliolumbar artery. It also receives a blood supply from the obturator, external iliac, and femoral arteries ^{[18] [19]}.