psoas

The psoas refers to a group of closely related muscles in the posterior abdominal wall and pelvis, chiefly the psoas major and the sometimes-present psoas minor. When combined with the iliacus, they form the iliopsoas, a primary hip flexor and a key stabilizer of the lumbar spine.

Anatomy and attachments

The psoas major arises from the sides of the T12 to L5 vertebral bodies and intervertebral discs, and from the transverse processes of the lumbar vertebrae. It descends through the abdomen to join the iliacus, and together they insert as the iliopsoas tendon on the lesser trochanter of the femur. The psoas minor is a small, variable muscle that lies anterior to the psoas major; it originates from the T12 to L1 vertebrae and typically inserts along the iliopectineal arch and the pectineal line. The nerve supply is from ventral rami of L1-L4 for the psoas major, and predominantly L1 for the psoas minor. Blood supply is provided by lumbar arteries and the iliolumbar artery.

Function

The iliopsoas is the principal hip flexor, with the psoas major contributing to flexion and, when the thigh is fixed, aiding trunk flexion and stabilization of the lumbar spine. The psoas minor, when present, plays a much smaller role in flexion and trunk stabilization. Together, these muscles influence posture and locomotion, and coordinate with the surrounding pelvic and abdominal musculature.

Clinical relevance

Tight or dysfunctional psoas muscles can contribute to lower back or hip pain and altered gait. Conditions such as psoas syndrome or psoas abscess are recognized clinical entities in certain contexts. Diagnosis and management typically involve physical examination, imaging as needed, and targeted physical therapy or, rarely, surgical intervention.