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Abductor Pollicis Longus Muscle Anatomy

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Abductor Pollicis Longus Muscle Anatomy

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The abductor pollicis longus (APL) has a long, fusiform belly that lies just distal to the supinator and is closely related to the extensor pollicis brevis. It’s located in the posterior compartment of the forearm.

Abductor Pollicis Longus Muscle Anatomy

The abductor pollicis longus origin is from the posterior surfaces of ulna, radius and interosseous membrane. It consists fundamentally of a superficial and a deep division, both terminating in one or more tendons:

  • The deep division is proximally situated, it is covered by the extensor digitorum muscle and consists of several muscle bellies; it terminates in a central tendon. The fibres are short, obliquely attached to the tendon in a pennate manner and close together. After the passage through the extensor retinaculum the tendon separates into many branches.
  • The superficial division is more distally situated, not covered by other muscles, lying superficial to the tendon of the deep part. The fibres are long, parallel to one another and form a thin layer. The tendon passes, together with the deep division, through the same compartment of the extensor retinaculum and inserts into the base of the 1st metacarpal.
See Also: Forearm Muscles Anatomy & Function

Sometimes one of abductor pollicis longus division may attach to the trapezium instead of the usual site at the base of the 1st metacarpal.

Abductor Pollicis Longus Muscle

The superficial part, with long thin fibres, presumably has the least strength while the deep part, with its larger number of fibres, is the most powerful.

Although deeply situated, the abductor pollicis longus emerges at the wrist as one of the outcropping muscles. Its tendon passes deep to the extensor retinaculum with the tendon of the extensor pollicis brevis in the common synovial tendinous sheath of the abductor pollicis longus and extensor pollicis brevis.

It’s innervated by the posterior interosseous nerve (C7 and C8) The continuation of the deep branch of the radial nerve.

It gets its blood supply from the posterior interosseous artery.

The abductor pollicis longus functions with the abductor pollicis brevis during abduction of the thumb and with the extensor pollicis muscles during extension of this digit.

OriginPosterior surfaces of ulna, radius and interosseous membrane
InsertionBase of 1st metacarpal
InnervationPosterior interosseous nerve (C7 and C8)
Blood SupplyPosterior interosseous artery
ActionAbducts thumb and extends it at carpometacarpal joint

To test the abductor pollicis longus, the thumb is abducted against resistance at the metacarpophalangeal joint. If acting normally, its tendon can be seen and palpated at the lateral side of the anatomical snuff box and on the lateral side of the adjacent extensor pollicis brevis tendon.

See Also: Finkelstein Test

References & More

  1. Cael, C. (2010). Functional anatomy: Musculoskeletal anatomy, kinesiology, and palpation for manual therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.
  2. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
  3. Clinically Oriented Anatomy – 8th Edition
  4. van Oudenaarde E. Structure and function of the abductor pollicis longus muscle. J Anat. 1991 Feb;174:221-7. PMID: 2032936; PMCID: PMC1256056. Pubmed
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