Psoas major varies a great deal in size and shape. It originates in the last thoracic and all lumbar vertebrae and inserts on the lesser trochanter of the femur. It traps the coxal bone and sacrum between its attachments.
It has two sections. One originates on vertebral bodies or T12-L4 and the other originates on the transverse processes of L1-L5. Nerve roots from the lumbar vertebrae pass between these sections. They blend together and then blend with the iliacus before inserting on the femur.
Lateral views in the standing position are not often seen. It highlights the sections and shows how psoas major bends around the pubic bone before inserting on the femur.
Origin – Psoas major usually originates from two sections. The anterior bellies originate from the bodies and intervertebral discs of T12-L4. The posterior portion originates from the transverse processes of L1-L5.
Insertion – Psoas major blends with the fibers of iliacus, crosses the pubic bone and inserts on the lesser trochanter of the femur.
Function – Psoas major is primarily seen as a hip flexor but also flexes the trunk laterally. Its other functions can get complicated. For example, it is largely seen as contributing extending the lumbar spine and compressing the lower lumbar vertebrae, however, when the lumbar is in reverse curve, the upper sections can, paradoxically, flex the lumbar spine.
Tony Preston has a practice in Atlanta, Georgia where he sees clients.
He has written and taught about anatomy, trigger points and cranial therapies since the mid-90s.