Extensor indicis muscle

Structure

It arises from the distal third of the dorsal part of the body of the 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.

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. The extensor indicis lacks the juncturae tendinum interlinking the tendons of the extensor digitorum on the dorsal side of the hand.

Variation

The extensor indicis proprius does not show much variation. It exists as a single tendon most of the time. Double tendons of the extensor indicis proprius was also reported.

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

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

Function

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

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

Additional images

|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.

Notes

References

• {{cite book | last = Platzer | first = Werner
• {{cite book | editor-last1 = Ross | editor-first1 = Lawrence M. | editor-last2 = Lamperti | editor-first2 = Edward D.

References

1. {{harvnb. Platzer. 2004
2. (1999). "Variations of the Extensor Indicis Muscle and Tendon". Journal of Hand Surgery, British Volume.
3. {{harvnb. Ross. Lamperti. 2006
4. (Nov–Dec 2011). "A comprehensive study of the extensor tendons to the medial four digits of the hand". Chang Gung Medical Journal.
5. "Double tendon of the Human Extensor Indicis Muscle provides "insight' into individual development -- Kumka 22 (1): 983.2 -- The FASEB Journal".
6. (1986-07-01). "The human extensor digitorum profundus muscle with comments on the evolution of the primate hand". Primates.
7. "Anatomy of the human body".
8. Straus, W.I.. (1941). "Phylogeny of human forearm extensors". Ann Hum Biol.