Which action is shared by psoas major and iliacus?

Which action is shared by psoas major and iliacus?

• A. External rotation
• B. Adduction
• C. Flexion and lateral rotation of thigh at hip
• D. Abduction

Answer: (C)

The shared action is hip flexion, with a note on rotation when the hip is flexed. Psoas major and iliacus merge to form the iliopsoas, the primary hip flexor, inserting on the lesser trochanter of the femur. They vigorously flex the thigh at the hip, bringing the femur forward. When the thigh is flexed, their pull also tends to rotate the femur laterally (external rotation) due to the direction of their fibers and the joint geometry. They do not primarily abduct or adduct the thigh, actions driven by other muscles such as the gluteals for abduction and the adductors for adduction.

The shared action is hip flexion, with a note on rotation when the hip is flexed. Psoas major and iliacus merge to form the iliopsoas, the primary hip flexor, inserting on the lesser trochanter of the femur. They vigorously flex the thigh at the hip, bringing the femur forward. When the thigh is flexed, their pull also tends to rotate the femur laterally (external rotation) due to the direction of their fibers and the joint geometry. They do not primarily abduct or adduct the thigh, actions driven by other muscles such as the gluteals for abduction and the adductors for adduction.