Psoas minor muscle
Anatomy and supply
The psoas minor muscle is a long, slim muscle of the hip joint that runs ventrally to the iliopsoas. Together they make up the inner hip muscles. The psoas minor originates from the lateral surface of the 12th thoracic and 1st lumbar vertebrae. Distally, its relatively long tendon inserts on the iliopubic eminence and pectineal line of the pubis. Additionally, fibers of the insertion tendon are attached to the iliac fascia.
The psoas minor is innervated by direct branches of the lumbar plexus (L1-L2). As the muscle lies deep inside the abdomen it is practically not possible to be felt from the outside. The psoas minor is an inconstant muscle and is not found in about 40-70% of all people. You often find instead a thin ligament or broadening of the medial part of the iliopsoas.
As an inner hip muscle the psoas minor contributes to the stabilization of the pelvis and hip joint. A unilateral contraction bends the lumbar vertebral column to the side (lateral flexion), while a bilateral activation bends it to the front (ventral flexion). All in all, this muscle's functions show that it plays a rather subordinate role.
Usually the muscle inserts at the pelvis but sometimes the insertion tendon can descend further down up to the femur making it proner to overstrain. In the long run, it becomes stiff and less flexible (psoas minor syndrome). In addition to the limited movement of the hip, this can also result in the development of a malposition of the vertebral column. The affected patients, mostly female teenagers, present with pain in the lower abdomen which is why the psoas minor syndrome is often mistaken for appendicitis. A simple surgical division of the tendon (tenotomy) can completely eliminate any discomfort and restore functionality.