View source for Extensor indicis muscle

{{Short description|Forearm muscle which extends the index finger}}
{{Infobox muscle
| Name        = Extensor indicis proprius
| Latin       = musculus extensor indicis
| Image       = Gray421.png
| Caption     = Transverse section across distal ends of [[Radius (bone)|radius]] and [[ulna]]. (Label "Ext. indic. prop." visible at bottom center.)
| Image2      = Extensor indicis muscle.png
| Caption2    = Posterior surface of the left forearm. Deep muscles. Extensor indicis muscle  is labeled in purple.
| Origin      = Posterior distal third of [[ulna]] and [[interosseous membrane]]
| Insertion   = [[Index finger]] ([[extensor hood]])
| Blood       = [[Posterior interosseous artery]]
| Nerve       = [[Posterior interosseous nerve]]
| Action      = [[Extension (kinesiology)|Extends]] [[index finger]], [[wrist]]
| Antagonist  =
}}
In [[human anatomy]], the '''extensor indicis (proprius)''' is a narrow, elongated [[skeletal muscle]] in the deep layer of the dorsal [[forearm]], placed medial to, and parallel with, the [[Extensor pollicis longus muscle|extensor pollicis longus]].  Its tendon goes to the [[index finger]], which it extends.

==Structure==
It arises from the distal third of the dorsal part of the [[body of ulna|body of the ulna]] and from the [[Interosseous membrane of the forearm|interosseous membrane]]. It runs through the fourth tendon compartment together with the [[extensor digitorum muscle|extensor digitorum]], from where it projects into the dorsal [[aponeurosis]] of the index finger.
<ref name="Platzer-168">{{harvnb|Platzer|2004| p=168}}</ref>

Opposite the head of the [[second metacarpal]] bone, it joins the ulnar side of the tendon of the extensor digitorum which belongs to the index finger.

Like the [[Extensor digiti minimi muscle|extensor digiti minimi]] (i.e. the extensor of the little finger), the tendon of the extensor indicis runs and inserts on the ulnar side of the tendon of the common extensor digitorum.<ref name=":0">{{Cite journal|url = http://ac.els-cdn.com/S0266768199902395/1-s2.0-S0266768199902395-main.pdf?_tid=c571af40-0e52-11e5-be3b-00000aab0f27&acdnat=1433818616_5933109180a86ad0bafc84c383724c12|journal = Journal of Hand Surgery, British Volume|volume = 24|issue = 5|pages = 575–578|access-date = 2015-06-09|doi = 10.1054/jhsb.1999.0239|pmid = 10597935|year = 1999|last1 = Komiyama|first1 = M.|last2 = Nwe|first2 = T. M.|last3 = Toyota|first3 = N.|last4 = Shimada|first4 = Y.|title = Variations of the Extensor Indicis Muscle and Tendon|s2cid = 23240783}}</ref> The extensor indicis lacks the [[juncturae tendinum]] interlinking the tendons of the extensor digitorum on the dorsal side of the hand.
<ref name="Ross-Lamperti-300">{{harvnb|Ross|Lamperti|2006| p=300}}</ref>

=== Variation ===
The extensor indicis proprius does not show much variation. It exists as a single tendon most of the time.<ref>{{Cite journal|title = A comprehensive study of the extensor tendons to the medial four digits of the hand|journal = Chang Gung Medical Journal|date = Nov–Dec 2011|issn = 2309-835X|pmid = 22196064|pages = 612–619|volume = 34|issue = 6|first1 = Prameela|last1 = Dass|first2 = Latha V.|last2 = Prabhu|first3 = Mangala M.|last3 = Pai|first4 = Varsha|last4 = Nayak|first5 = Ganesh|last5 = Kumar|first6 = Jiji P.|last6 = Janardhanan}}</ref>  Double tendons of the extensor indicis proprius was also reported.<ref name=":0" /><ref>{{Cite web|title = Double tendon of the Human Extensor Indicis Muscle provides "insight' into individual development -- Kumka 22 (1): 983.2 -- The FASEB Journal|url = http://www.fasebj.org/cgi/content/meeting_abstract/22/1_MeetingAbstracts/983.2|website = www.fasebj.org|access-date = 2015-06-09}}</ref><ref>{{Cite journal|title = The human extensor digitorum profundus muscle with comments on the evolution of the primate hand|journal = Primates|date = 1986-07-01|issn = 0032-8332|pages = 293–319|volume = 27|issue = 3|doi = 10.1007/BF02382073|first1 = M. Ashraf|last1 = Aziz|first2 = Samuel Strong|last2 = Dunlap|s2cid = 39525970}}</ref>

It is known that the extensor indicis proprius inserts to the index finger on the ulnar side of the extensor digitorum.<ref>{{Cite web|title = Anatomy of the human body|url = https://archive.org/stream/anatomyofhumanbo1918gray#page/456/mode/2up/search/456|website = archive.org|access-date = 2015-06-09}}</ref> However, the insertion on the radial side of the common extensor digitorum infrequently seen, namely the ''extensor indicis radialis''.<ref name=":0" /> Split tendons of the muscle inserting on both ulnar and the radial side of the common extensor digitorum was also reported.<ref name=":0" />

Anomalous hand extensors including the [[extensor medii proprius]] and the [[Extensor indicis et medii communis muscle|extensor indicis et medii communis]] are often seen as variations of the extensor indicis <ref name=":0" /> due to the shared characteristics and embryonic origin.<ref>{{Cite journal|title = Phylogeny of human forearm extensors|last = Straus|first = W.I.|date = 1941|journal = Ann Hum Biol|issue = 13|pages = 203–238}}</ref>

==Function==
The extensor indicis [[Extension (kinesiology)|extends]] the [[index finger]], and by its continued action assists in extending ([[dorsiflexion]]) the [[wrist]] and the [[midcarpal joint]]s.<ref name="Platzer-168" />

Because the index finger and little finger have separate extensors, these fingers can be moved more independently than the other fingers.<ref name="Ross-Lamperti-300" />

==Additional images==
{{gallery
| height = 150|width=150|Image:Gray424.png|The mucous sheaths of the tendons on the back of the wrist. (Extensor indicis proprius visible going into second digit.)
 |Image:Gray214.png|Bones of left forearm. Posterior aspect.
 |Image:Musculusextensorindicisproprius.png|Posterior surface of the forearm. Deep muscles.
 |Image:Carpal-Tunnel.svg|Transverse section across the wrist and digits.
 |File:Extensor indicis muscle.jpg|Extensor indicis muscle
|File:Slide4RRRRR.JPG| Extensor indicis muscle
|File:Slide4SSSS.JPG|Extensor indicis muscle
|File:Slide10SSSS.JPG|Extensor indicis muscle
|File:Slide14TTTT.JPG|Extensor indicis muscle
|File:Slide1MAM.JPG|Muscles of hand. Posterior view.
|File:Slide2TAT.JPG|Muscles of hand. Posterior view.
}}

== See also ==
* [[Extensor digitorum muscle|Extensor digitorum]]
* [[Extensor medii proprius muscle|Extensor medii proprius]]
* [[Extensor indicis et medii communis muscle|Extensor indicis et medii communis]]

==Notes==
{{Reflist|colwidth=30em}}

==References==
{{Gray's}}
* {{cite book | last = Platzer | first = Werner
| title     = Color Atlas of Human Anatomy, Vol. 1: Locomotor System
| publisher = [[Thieme Medical Publishers|Thieme]] | isbn = 3-13-533305-1<!---US: 1-58890-159-9--->
| year      = 2004 | edition = 5th
}}
* {{cite book | editor-last1 = Ross | editor-first1 = Lawrence M. 
| editor-last2     = Lamperti | editor-first2 = Edward D. 
| title     = Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System
| publisher = Thieme | year = 2006 | isbn = 978-1-58890-419-5
}}

==External links==
* {{SUNYAnatomyLabs|09|05|01|06}} - "Extensor Region of Forearm and Dorsum of Hand: Deep Muscles of Extensor Region"
* {{NormanAnatomy|lesson5musofpostforearm}}
* {{DukeOrtho|Extensor_indicis}}
* {{cite journal
 |last1   = Ritter
 |first1  = Merrill A.
 |last2   = Inglis
 |first2  = Allen E.
 |title   = The Extensor Indicis Proprius Syndrome
 |journal = J Bone Joint Surg Am
 |volume  = 51
 |year    = 1969
 |issue   = 8
 |pages   = 1645–1648
 |url     = http://www.ejbjs.org/cgi/reprint/51/8/1645.pdf
 |doi     = 10.2106/00004623-196951080-00016
 |pmid    = 5357184
}}{{Dead link|date=March 2024 |bot=InternetArchiveBot |fix-attempted=yes }}

{{Muscles of upper limb}}
{{Portal bar|Anatomy}}
{{Authority control}}

[[Category:Muscles of the upper limb]]