Final answer:
The iliopsoas muscle, consisting of the psoas major and iliacus, inserts at the lesser trochanter of the femur, which allows it to act as a primary flexor of the hip joint.
Step-by-step explanation:
The iliopsoas muscle, comprising the psoas major and iliacus muscles, inserts at the lesser trochanter of the femur.
The iliopsoas muscle group is essential for flexing the thigh at the hip and consists of two muscles: the psoas major and the iliacus. The psoas major originates from the vertebrae and discs of the lumbar spine and travels downward through the pelvic region. The iliacus originates from the iliac fossa, which is a large, spoon-shaped region on the interior aspect of the ilium. These two muscles converge and pass beneath the inguinal ligament to insert together onto the lesser trochanter of the femur via a shared tendon. This insertion point is critical as it allows the iliopsoas group to act as a powerful flexor of the hip joint, enabling movements such as lifting the knee toward the chest. Additionally, because of its attachment to the spine, the psoas major also helps to maintain the normal lumbar lordosis (inward curvature) of the lower spine and assists in lateral rotation of the thigh.