Definition

By: Gregory R. Waryasz, MD

The flexor pollicis longus muscle of the musculoskeletal system is characterized by being the long flexor of the thumb and the only flexor of the distal phalanx of the thumb.

It is part of the forearm.  It consists of skeletal muscle fibers.

Its unique structural features include it covering the anterior radius distal to the supinator attachment. It is a flat tendon as it courses deep to the flexor retinaculum. The flexor pollicis longus lies in its own synovial sheath.

The origin is the anterior surface of the radius and interosseous membrane.

The insertion is the base of the distal phalanx of the thumb.

The blood supply is from the anterior interosseous artery and venous drainage is from the accompanying veins.

The innervation is from the anterior interosseous nerve.

The flexor pollicis longus muscle as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.

The function of the flexor pollicis longus is to flex the interphalangeal joint of the thumb.  It also plays a role in flexing the metacarpophalangeal joint and the carpal-metacarpal articulations.  The synergists are the flexor pollicus brevis and the adductor pollicis

Common diseases include tendon rupture, tenosynovitis, and congenital absence

Tendon rupture can occur with trauma.

Tenosynovitis of the flexor tendons can lead to the trigger finger phenomenon.

Congenital absence can occur with a variety of hypoplastic conditions of the thumb.

Commonly used diagnostic procedures include clinical history, physical exam, x-ray, and MRI.

It is usually treated with rest, NSAIDs, physical therapy, splinting, and corticosteroid injection for tenosynovitis.  Tenosynovitis causing a triggering phenomenon may require a release of the A1 pulley.  Tendon rupture may require surgery.

References

Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.

Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.

Wheeless’ Textbook of Orthopaedics: Flexor Pollicis Longus (http://www.wheelessonline.com/ortho/flexor_pollicis_longus)