The psoas minor does contribute to the iliopsoas muscle. The iliacus and psoas major form the iliopsoas, which is surrounded by the iliac fascia. The iliacus and psoas major comprise the iliopsoas group. As part of the iliopsoas, psoas major contributes to flexion in the hip joint. The iliopsoas () refers to the joined psoas and the iliacus muscles. This plexus lies within the psoas major muscle. They proceed anterior and inferior along the medial border of the psoas major muscles. The plexus is formed lateral to the intervertebral foramina and passes through psoas major. Psoas can be palpated with active flexion of the hip. Innervation of the psoas major is through the anterior rami of L1 to L3 nerves. The infection can spread into the psoas muscle sheath. It passes downwards, pierces the psoas major and emerges from its anterior surface. The nerve then traverses the retroperitoneum, descending over the anterior surface of the psoas. If abdominal pain results, it is a "positive psoas sign". The iliacus and psoas major perform different actions when postural changes occur.