Psoas Minor: Origin, Insertion, Nerve, Action & Psoas Minor Syndrome

The Psoas Minor is a long, slender muscle located anterior to the Psoas Major. It is considered a vestigial muscle, meaning it has lost most of its original function through evolution. It is absent in approximately 40-60% of the human population.

[Image of Psoas Major muscle anatomy]

Quick Anatomy Snapshot

Prevalence	Absent in 40% to 60% of people (often present on only one side).
Origin (Proximal)	Sides of the bodies of T12 and L1 vertebrae and the intervertebral disc between them.
Insertion (Distal)	Pectineal Line of the Pubis and the Iliopectineal Eminence (does NOT attach to femur).
Nerve Supply	Anterior Ramus of L1.
Blood Supply	Lumbar Arteries.
Primary Actions	Trunk Flexion: Very weak assistance. Pelvic Tilt: Weak posterior tilt of the pelvis.

Deep Dive: The Muscle That Disappeared

In quadrupedal animals (like dogs and rabbits), the Psoas Minor is a large, significant muscle used to arch the back while running. In upright humans, it has become largely obsolete.

1. "On Top" of the Major

The muscle belly of the Psoas Minor sits directly on the anterior surface of the Psoas Major. It has a short muscle belly and a very long, flat, glistening tendon that runs down the front of the Psoas Major to reach the pelvis.

2. The Hip Flexor Myth

Unlike the Psoas Major, the Psoas Minor does not cross the hip joint. It stops at the pelvic brim (pubis). Therefore, it cannot flex the hip. Its only mechanical action is to pull the pelvis upward or flex the lumbar spine very weakly.

Physio Corner: Clinical Relevance

💪 Functional Fact: Because it is expendable, the Psoas Minor tendon is sometimes harvested by surgeons for use in reconstructive surgery elsewhere in the body.

Palpation

It is virtually impossible to palpate the Psoas Minor distinct from the Psoas Major due to its depth in the abdomen and its variable presence. If present, it tenses along with the Psoas Major during trunk flexion.

⚠️ Clinical Pathology: Psoas Minor Syndrome
In rare cases, a tight Psoas Minor tendon can "snap" over the pelvic brim or become spastic, causing pain in the lower quadrant of the abdomen. This pain can mimic Appendicitis (on the right) or Diverticulitis (on the left), leading to diagnostic confusion.

Manual Muscle Testing (MMT)

There is no specific manual muscle test for the Psoas Minor because it cannot be isolated from the Psoas Major and Rectus Abdominis.

Testing Tip: Any test for trunk flexion (like a sit-up) involves this muscle if it is present, but its contribution is negligible compared to the abdominals.

Frequently Asked Questions

How do I know if I have this muscle?

You generally can't tell without MRI imaging or surgery. Functional strength is identical whether you have it or not.

Does it help stabilization?

It attaches to the deep fascia (Iliac Fascia). Some theories suggest it might act as a tensioner of the iliac fascia, possibly aiding in proprioception or stabilizing the underlying Psoas Major.

Is it related to Plantaris/Palmaris Longus?

Yes, in the sense that they are all vestigial muscles characterized by small bellies and long tendons, and are frequently absent in the population.

Test Your Knowledge: Psoas Minor Quiz

1. What percentage of the population is missing the Psoas Minor?

2. Where does the Psoas Minor insert?

3. Which nerve supplies the Psoas Minor?

4. Does the Psoas Minor cross the hip joint?

5. Where does the Psoas Minor lie relative to the Psoas Major?

6. Psoas Minor Syndrome on the right side can mimic:

7. What is the origin of Psoas Minor?

8. What is the primary action of Psoas Minor?

9. The tendon of Psoas Minor blends with which fascia?

10. True or False: Psoas Minor is a powerful stabilizer of the lumbar spine.

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Neumann, D. A. (2016). Kinesiology of the Musculoskeletal System. 3rd ed. Elsevier.