Adductor Pollicis: Origin, Insertion, Nerve, Action & Froment's Sign

The Adductor Pollicis is a distinctive, two-headed muscle located deep in the palm of the hand. It creates the fleshy bulk of the "web space" between the thumb and index finger. While most thumb muscles are powered by the median nerve, this muscle is unique as it is the only thumb muscle supplied by the ulnar nerve.

[Image of Adductor Pollicis muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	1. Oblique Head: Bases of 2nd and 3rd Metacarpals, Capitate bone. 2. Transverse Head: Anterior shaft of the 3rd Metacarpal.
Insertion (Distal)	Medial (Ulnar) side of the base of the Proximal Phalanx of the Thumb (via the ulnar sesamoid).
Nerve Supply	Deep Branch of Ulnar Nerve (C8, T1).
Blood Supply	Deep Palmar Arch.
Primary Actions	Adduction: Pulls the thumb towards the index finger (palm). Opposition Assistance: Helps bring the thumb across the palm.

Deep Dive: The Triangular Muscle

The Adductor Pollicis is fan-shaped, originating widely from the center of the palm and narrowing to insert onto the thumb.

1. The Two Heads

The Transverse Head is the most distinct, forming the triangular web between the thumb and index finger. The Oblique Head lies deeper. Anatomically, the Radial Artery passes between these two heads to enter the deep palm and form the Deep Palmar Arch.

2. Not a "Thenar" Muscle

Although it acts on the thumb, the Adductor Pollicis is not considered part of the Thenar Eminence (which includes APB, FPB, and OP). It lies deeper and has a different nerve supply (Ulnar vs. Median).

Physio Corner: Clinical Relevance

💪 Functional Fact: This muscle provides up to 50% of your grip strength! It creates the powerful "key pinch" (lateral pinch) used to hold a key or a credit card between the thumb and the side of the index finger.

Palpation

Have the patient rest their hand palm up. Ask them to pull their thumb in towards their index finger (adduct). Palpate the web space on the palmar side. The fleshy muscle you feel bulking up in the web space is the Adductor Pollicis.

⚠️ Clinical Pathology: Froment's Sign
This is a classic test for Ulnar Nerve Palsy. Ask the patient to hold a piece of paper between their thumb and index finger (lateral pinch) while you pull it away.

Positive Sign: Because the Adductor Pollicis (Ulnar n.) is weak, the patient compensates by flexing the IP joint of the thumb using the Flexor Pollicis Longus (Median n.). This flexion of the thumb tip is Froment's Sign.

Manual Muscle Testing (MMT)

Testing the ability to pull the thumb into the palm against resistance.

Testing Tip: Ensure the patient keeps the thumb straight (IP extended) to prevent substitution by the Flexor Pollicis Longus.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Hand supinated (palm up) or resting on ulnar side. Action: Patient lifts the thumb towards the palm (adduction) from an abducted position. Resistance: Applied at the medial side of the proximal phalanx, pulling the thumb away (into abduction). Grade 3: Full range against gravity. Grade 4/5: Holds against pressure.
Grade 2 (Gravity Eliminated)	Position: Hand pronated (palm down) on the table. Action: Patient slides the thumb towards the index finger. Result: Full range of sliding motion.
Grade 0, 1 (Palpation)	Action: Palpate the palmar web space. Cue: "Squeeze your thumb to your finger." Grade 1: Trace contraction felt. Grade 0: No activity.

Frequently Asked Questions

Why does Ulnar nerve injury weaken thumb adduction?

Because the Adductor Pollicis is exclusively innervated by the Deep Branch of the Ulnar Nerve. Without it, the thumb cannot forcefully pinch against the index finger.

What is Jeanne's Sign?

Similar to Froment's sign, Jeanne's sign is seen in ulnar nerve palsy. It involves hyperextension of the thumb MCP joint during pinch grip due to instability from the paralyzed Adductor Pollicis.

Does it attach to a sesamoid bone?

Yes. The Adductor Pollicis inserts into the Ulnar (Medial) Sesamoid at the thumb MCP joint. The Flexor Pollicis Brevis inserts into the Radial (Lateral) Sesamoid.

Test Your Knowledge: Adductor Pollicis Quiz

1. Which nerve supplies the Adductor Pollicis?

2. Which anatomical structure passes between the two heads of the Adductor Pollicis?

3. A positive Froment's Sign indicates weakness of which muscle?

4. Where does the Transverse Head originate?

5. Is the Adductor Pollicis considered part of the Thenar Eminence?

6. The primary action of Adductor Pollicis is to pull the thumb toward the:

7. The Adductor Pollicis creates which type of grip?

8. Which sesamoid bone does the Adductor Pollicis insert into?

9. During Froment's Sign, the patient compensates by flexing which joint?

10. Where does the Adductor Pollicis insert?

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.
• Magee, D. J. (2014). Orthopedic Physical Assessment. 6th ed. Elsevier.