Extensor indicis muscle

Extensor indicis proprius
Transverse section across distal ends of radius and ulna. (Label "Ext. indic. prop." visible at bottom center.)
Posterior surface of the left forearm. Deep muscles. Extensor indicis muscle is labeled in purple.
Details
Origin	Posterior distal third of ulna and interosseous membrane
Insertion	Index finger (extensor hood)
Artery	Posterior interosseous artery
Nerve	Posterior interosseous nerve
Actions	Extends index finger, wrist
Identifiers
Latin	musculus extensor indicis
TA98	A04.6.02.052
TA2	2515
FMA	38524
Anatomical terms of muscle [edit on Wikidata]

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. Its tendon goes to the index finger, which it extends.

It arises from the distal third of the dorsal part of the body of ulna and from the interosseous membrane. It runs through the fourth tendon compartment together with the extensor digitorum, from where it projects into the dorsal aponeurosis of the index finger. ^[1]

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 (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.^[2] The extensor indicis lacks the juncturae tendinum interlinking the tendons of the extensor digitorum on the dorsal side of the hand. ^[3]

The extensor indicis proprius does not show much variation. It exists as a single tendon most of the time.^[4] Double tendons of the extensor indicis proprius was also reported.^[2][5][6]

It is known that the extensor indicis proprius inserts to the index finger on the ulnar side of the extensor digitorum.^[7] However, the insertion on the radial side of the common extensor digitorum infrequently seen, namely the extensor indicis radialis.^[2] Split tendons of the muscle inserting on both ulnar and the radial side of the common extensor digitorum was also reported.^[2]

Anomalous hand extensors including the extensor medii proprius and the extensor indicis et medii communis are often seen as variations of the extensor indicis ^[2] due to the shared characteristics and embryonic origin.^[8]

The extensor indicis extends the index finger, and by its continued action assists in extending (dorsiflexion) the wrist and the midcarpal joints.^[1]

Because the index finger and little finger have separate extensors, these fingers can be moved more independently than the other fingers.^[3]

• Extensor digitorum
• Extensor medii proprius
• Extensor indicis et medii communis

This article incorporates text in the public domain from page 456 of the 20th edition of Gray's Anatomy (1918)

• Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1.
• Ross, Lawrence M.; Lamperti, Edward D., eds. (2006). Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. ISBN 978-1-58890-419-5.

• Anatomy photo:09:05-0106 at the SUNY Downstate Medical Center - "Extensor Region of Forearm and Dorsum of Hand: Deep Muscles of Extensor Region"
• lesson5musofpostforearm at The Anatomy Lesson by Wesley Norman (Georgetown University)
• Extensor indicis at the Duke University Health System's Orthopedics program
• Ritter, Merrill A.; Inglis, Allen E. (1969). "The Extensor Indicis Proprius Syndrome" (PDF). J Bone Joint Surg Am. 51 (8): 1645–1648. doi:10.2106/00004623-196951080-00016. PMID 5357184.^{[permanent dead link]}