Abductor pollicis longus
The Abductor pollicis longus (APL) is one of a deep extensor of the forearm and is responsible for facilitating movement and stabilization of the thumb. It's tendon is present in the first extensor compartment of the wrist.
The APL originates from the posterior surface of Ulna, the middle third of the posterior surface of Radius and the radio-ulnar interosseous membrane.
It inserts into the base of first Metacarpal. Accessory tendons of APL are also found to insert into the base of trapezium and thenar structures. 
It is supplied by the Posterior Interosseous nerve (C7-C8) which is a continuation of the deep branch of Radial nerve.
Posterior interosseous artery
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.
The most important clinical condition involving the APL, usually along with the Extensor pollicis brevis is the DeQuervain's Syndrome. It is characterized 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.
The strength of APL is assessed by asking the subject to abduct the thumb with the forearm in neutral psotioin. Resistance is applied against the lateral aspect ofg the distal end of first metacarpal in the direction of adduction of thumb.
The test used for clinical diagnosis of DeQuervains is known as the Finklestein's test. The patient is asked to amke 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.
Management of DeQuervain's syndrome would depend on the severity of the cindition and can include:
- Electrotherapy modalities including local Ultrasound and TENS application
- Cold packs/heat packs
- Manual therapy including myofascial release of the tendons and stretching
- Stregnth training for long standing conditions
- Thumb splinting, medication and taping can be done for very painful or acute cases
- 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
- Agur AM, Dalley AF. Grant's Atlas of Anatomy. 12th edition. Canada: Lippincott Williams & Wilkins;2009
- 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
- Department of Radiology, University of Washington. Abductor pollicis longus. https://rad.washington.edu/muscle-atlas/abductor-pollicis-longus/ (accessed on 11 Nov 2017)
- 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
- 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
- Arend CF. Tenosynovitis and synovitis of the first extensor compartment of the wrist: what sonographers should know. Radiol Bras 2012;45(4):219-224
- 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)