Lumbricals of the hand
{{Short description|Muscles in the central compartment of the hand}}
{{for|the foot muscles|Lumbrical muscle of the foot}}
{{Infobox muscle
| Name = Lumbricals of the hand
| Latin = musculi lumbricales manus
| Image = Lumbricales (hand).png
| Caption = The muscles of the left hand. Palmar surface. (first lumbricalis labeled at bottom right of muscular group)
| Origin = Flexor digitorum profundus
| Insertion = Extensor expansion
| Blood = Superficial palmar arch, common palmar digital arteries, deep palmar arch, dorsal digital artery
| Nerve = Third and fourth deep branch of ulnar nerve, first and second median nerve
| Action = Flex metacarpophalangeal joints, extend interphalangeal joints
| part_of = Hand
}}
The lumbricals are intrinsic muscles of the hand that flex the metacarpophalangeal joints, and extend the interphalangeal joints.{{cite book | vauthors = Gosling JA, Harris PF, Humpherson JR, Whitmore I, Willan PL | title = Human Anatomy: Color Atlas and Textbook | edition = 5th | year = 2008 | publisher = Mosby | location = Philadelphia | isbn = 978-0-7234-3451-1 | ref = Gosling }}
The lumbrical muscles of the foot also have a similar action, though they are of less clinical concern.
Structure
The lumbricals are four, small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone. Instead, they attach proximally to the tendons of flexor digitorum profundus,{{cite journal | vauthors = Wang K, McGlinn EP, Chung KC | title = A biomechanical and evolutionary perspective on the function of the lumbrical muscle | journal = The Journal of Hand Surgery | volume = 39 | issue = 1 | pages = 149–55 | date = January 2014 | pmid = 24369943 | pmc = 4155599 | doi = 10.1016/j.jhsa.2013.06.029 }} and distally to the extensor expansions. The first and second lumbricals are unipennate, while the third and fourth lumbricals are bipennate.{{cite journal | vauthors = Schweizer A | title = Lumbrical tears in rock climbers | journal = Journal of Hand Surgery | volume = 28 | issue = 2 | pages = 187–9 | date = April 2003 | pmid = 12631495 | doi = 10.1016/S0266-7681(02)00250-4 | s2cid = 244111 | citeseerx = 10.1.1.539.6140 }}
| class="wikitable"
| # | Form | Origin | Insertion |
| First | unipennate | It originates from the radial side of the most radial tendon of the flexor digitorum profundus (corresponding to the index finger). | It passes posteriorly along the radial side of the index finger to insert on the extensor expansion near the metacarpophalangeal joint. |
| Second | unipennate | It originates from the radial side of the second most radial tendon of the flexor digitorum profundus (which corresponds to the middle finger). | It passes posteriorly along the radial side of the middle finger and inserts on the extensor expansion near the metacarpophalangeal joint. |
| Third | bipennate | One head originates on the radial side of the flexor digitorum profundus tendon corresponding to the ring finger, while the other originates on the ulnar side of the tendon for the middle finger. | The muscle passes posteriorly along the radial side of the ring finger to insert on its extensor expansion. |
| Fourth | bipennate | One head originates on the radial side of the flexor digitorum profundus tendon corresponding to the little finger, while the other originates on the ulnar side of the tendon for the ring finger. | The muscle passes posteriorly along the radial side of the little finger to insert on its extensor expansion. |
{{Clear}}
=Nerve supply=
The first and second lumbricals (the most radial two) are innervated by the median nerve. The third and fourth lumbricals (most ulnar two) are innervated by the deep branch of ulnar nerve.{{cite journal | vauthors = Lauritzen RS, Szabo RM, Lauritzen DB | title = Innervation of the lumbrical muscles | journal = Journal of Hand Surgery (Edinburgh, Scotland) | volume = 21 | issue = 1 | pages = 57–8 | date = February 1996 | pmid = 8676031 | doi = 10.1016/s0266-7681(96)80013-1 | s2cid = 8084761 }}
This is the usual innervation of the lumbricals (occurring in 60% of individuals). However 1:3 (median:ulnar - 20% of individuals) and 3:1 (median:ulnar - 20% of individuals) also exist. The lumbrical innervation always follows the innervation pattern of the associated muscle unit of flexor digitorum profundus (i.e. if the muscle units supplying the tendon to the middle finger are innervated by the median nerve, the second lumbrical will also be innervated by the median nerve).{{cite book |last1=Sinnatamby |first1=Chummy S. | name-list-style = vanc |title=Last's Anatomy: Regional and Applied |date=1999 |publisher=Churchill Livingstone |location=Edinburgh |isbn=978-0-443-05611-6 |edition=10th | pages = 64, 82 }}
=Blood supply=
Four separate sources supply blood to these muscles: the superficial palmar arch, the common palmar digital artery, the deep palmar arch, and the dorsal digital artery.{{cite journal | vauthors = Zbrodowski A, Mariéthoz E, Bednarkiewicz M, Gajisin S | title = The blood supply of the lumbrical muscles | journal = Journal of Hand Surgery | volume = 23 | issue = 3 | pages = 384–8 | date = June 1998 | pmid = 9665531 | doi = 10.1016/S0266-7681(98)80063-6 | s2cid = 26384944 }}
Function
The lumbrical muscles, with the help of the interosseous muscles, simultaneously flex the metacarpophalangeal joints while extending both interphalangeal joints of the digit on which it inserts. The lumbricals are used during an upstroke in writing.
Etymology
The term "lumbrical" comes from the Latin, meaning "worm".{{Cite journal|last1=Bozer|first1=Cüneyt|last2=Uzmansel|first2=Deniz|last3=Dönmez|first3=Didem|last4=Parlak|first4=Muhammed|last5=Beger|first5=Orhan|last6=Elvan|first6=Özlem|date=2018-12-01|title=The effects of the communicating branch between medial and lateral plantar nerves on the innervations of the foot lumbrical muscles|url=http://www.sciencedirect.com/science/article/pii/S000327781730624X|journal=Journal of the Anatomical Society of India|language=en|volume=67|issue=2|pages=130–132|doi=10.1016/j.jasi.2018.11.006|s2cid=81678124 |issn=0003-2778}}
Additional images
File:Gray416.png|Tendons of forefinger and vincula tendina
File:Slide2yyy.JPG|Lumbricals of the hand
File:Slide5RRR.JPG|Lumbricals of the hand
File:Slide14RRR.JPG|Lumbricals muscle
File:Slide6PPP.JPG|Lumbricals muscle
File:Slide4VVV.JPG|Lumbricals muscle
File:Slide4AAAA.JPG|Lumbricals muscle
File:Slide9AAAA.JPG|Lumbricals muscle
File:Slide1MAI.JPG|Muscles of hand, cross section
File:Slide1dsds.JPG|Wrist joint. Deep dissection. Anterior, palmar view
File:Slide2dsds.JPG|Wrist joint. Deep dissection. Anterior, palmar view
File:Slide3dsds.JPG|Wrist joint. Deep dissection. Anterior, palmar view