Abductor pollicis longus

Original Editor - Vidhu Sindwani

Top Contributors - Vidhu Sindwani, Kim Jackson and Priya Gulla

Description

The Abductor pollicis longus (APL) is one of a deep extensor of the forearm and is responsible for facilitating movement and stabilisation of the thumb. It's tendon is present in the first extensor compartment of the wrist.[1] It lies immediately below the supinator and sometimes unite with it. The muscle belly consists fundamentally of three parts which results into two divisions of tendons. [2]

Origin & Insertion

Abductorpollicislongus.png
The first part of the abductor pollicis muscle is a deep part which originates from the ulna, interosseous membrane and radius and is covered by extensor digitorum longus. It has numerous subdivisions of belly (all arranged in a parallel fashion) which terminates in a central tendon. The fibres of first part are short, obliquely attached to a tendon in a pennate fashion. After its passage through the first compartment of extensor retinaculum, the deep tendon separates into several branches and is ultimately inserted into trapezium, abductor pollicis brevis, opponens pollicis, capsule and anterior oblique ligament.[2]

The other two parts of abductor pollicis longus are superficial. One of them originates from the ulna and interosseous membrane whereas the other originates from the deep fascia of forearm and the radius. These two parts are connected to the third deep part by a small area of connective tissues and terminates in a tendon to metacarpal 1[2].

Nerve Supply

It is supplied by the Posterior Interosseous nerve (C7-C8) which is a continuation of the deep branch of Radial nerve.[3]

Artery

Posterior interosseous artery[4]

Function


The main functions of APL include abduction of the thumb and extension of the first carpo-metacarpal joint. It also assists in radial deviation and flexion of the wrist.[5]

Clinical Relevance

The most important clinical condition involving the APL, usually along with the Extensor pollicis brevis is the DeQuervain's Syndrome. It is characterised by thickening and and inflammation of tendons of APL and EPB resulting in pain and swelling in the first extensor compartment of wrist. Pain increases on movements of thumb making the tendons more susceptible to degeneration and lesions[6].

Assessment

The strength of APL is assessed by asking the subject to abduct the thumb with the forearm in neutral position. Resistance is applied against the lateral aspect of the distal end of first metacarpal in the direction of adduction of the thumb.[5]

The test used for clinical diagnosis of DeQuervains is known as the Finklestein's test. The patient is asked to make a fist with the thumb inside the fingers. The therapist/examiner passively deviates the wrist to the ulnar side. A positive test is indicated by pain over the radial styloid process at the site of the tendons of APL and EPB.[7]

Treatment

Management of DeQuervain's syndrome would depend on the severity of the condition and can include[8]:

  1. Electrotherapy modalities including local Ultrasound and TENS application
  2. Cold packs/heat packs
  3. Manual therapy including myofascial release of the tendons and stretching
  4. Strength training for long standing conditions
  5. Thumb splinting, medication and taping can be done for very painful or acute cases

Resources

References

  1. Tewari J, Mishra PR, Tripathi SK. Anatomical variation of Abductor pollicis longus in Indian population: A cadaveric study. Indian J Orthop 2015;49:549-53
  2. 2.0 2.1 2.2 Elvire Van Oudenaarde. Structure and function of abductor pollicis longus muscle. Journal of Anatomy. 1991, 174: 221-227
  3. Abrams RA, Ziets RJ, Lieber RL, Botte MJ. Anatomy of the radial nerve motor branches in the forearm. The Journal of Hand Surgery 1997 Mar;22A(2):232-37
  4. Department of Radiology, University of Washington. Abductor pollicis longus. https://rad.washington.edu/muscle-atlas/abductor-pollicis-longus/ (accessed on 11 Nov 2017)
  5. 5.0 5.1 Kendall FP, McCreary EK, Provance PG, Rogers MM, Romany WA. Muscles testing and function with posture and pain. 5th ed. USA: Lippincott Williams & Wilkins; 2005. 261p
  6. Rosa RC, de Oliveira KM, Leo JA, Elias BA, dos Santos PR, de Santiago HA. Anomalous bilateral contribution of extensor pollicis longus and muscle fusion of the first compartment of the wrist. Rev Bras Ortop 2016;51(2):235-38
  7. Arend CF. Tenosynovitis and synovitis of the first extensor compartment of the wrist: what sonographers should know. Radiol Bras 2012;45(4):219-224
  8. Morphopedics. Physical therapy management of DeQuervai's disease. http://morphopedics.wikidot.com/physical-therapy-management-of-de-quervain-s-disease-tenosyn (accessed on 11 Nov 2017)