The flexor pollicis longus (/ˈflɛksərˈpɒlɪsɪsˈlɒŋɡəs/; FPL, Latin flexor, bender; pollicis, of the thumb; longus, long) is a
muscle in the
forearm and
hand that flexes the thumb. It lies in the same plane as the
flexor digitorum profundus. This muscle is unique to humans, being either rudimentary or absent in other primates.[1] A meta-analysis indicated accessory flexor pollicis longus is present in around 48% of the population.[2]
Human anatomy
Origin and insertion
It arises from the grooved anterior (side of palm) surface of the body of the
radius,[3] extending from immediately below the
radial tuberosity and oblique line to within a short distance of the
pronator quadratus muscle.[4] An occasionally present
accessory long head of the flexor pollicis longus muscle is called 'Gantzer's muscle'.[5] It may cause compression of the
anterior interosseous nerve.[5]
Modern humans are unique among
hominids in having a flexor pollicis longus (FPL) muscle belly that is separate from that of the
flexor digitorum profundus (FDP). While the FPL is not a separate muscle belly in extant
great apes, a distinct tendon from the FDP belly might be present. In some individuals, this tendon tend to act more like a
ligament, which restricts extension of the
interphalangeal joint of the thumb. In
orangutans there is a tendon similar in insertion and function to the FPL in humans, but which has an intrinsic origin on the oblique head of the
adductor pollicis.[10]
Lesser apes (i.e.
gibbons) and
Old World monkeys (e.g.
baboons) share an extrinsic FPL muscle tendon with humans. In most lesser apes, the FPL belly is separate from the FDP belly, but in baboons, the FPL tendon bifurcates from the FDP tendon at the wrist within the
carpal tunnel and, because of the lack of differentiation in both the FDP and FPL
musculature, it is unlikely that baboons can control individual digits independently.[10]
^Fernandez DL (2009-01-01). "Chapter 56: Osteotomy for Extra-articular Malunion of the Distal Radius". In Slutsky DJ, Osterman AL (eds.). Fractures and Injuries of the Distal Radius and Carpus. Philadelphia: W.B. Saunders. pp. 529–541.
doi:
10.1016/b978-1-4160-4083-5.00058-5.
ISBN978-1-4160-4083-5.
^
abcdefGray 1918, Flexor Pollicis Longus, paras 20, 25
^Lutsky KF, Giang EL, Matzon JL (January 2015). "Flexor tendon injury, repair and rehabilitation". The Orthopedic Clinics of North America. 46 (1): 67–76.
doi:
10.1016/j.ocl.2014.09.004.
PMID25435036.
^Preston DC, Shapiro BE (2013-01-01). "Chapter 18: Proximal Median Neuropathy". In Preston (ed.). Electromyography and Neuromuscular Disorders (Third ed.). pp. 289–297.
^Hamitouche K, Roux JL, Baeten Y, Allieu Y (May 2000). "[Linburg-Comstock syndrome. Epidemiologic and anatomic study, clinical applications]". Chirurgie de la Main. 19 (2): 109–15.
doi:
10.1016/s1297-3203(00)73468-8.
PMID10904829.