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Year : 2021  |  Volume : 15  |  Issue : 1  |  Page : 30-32

A variation: An extra tendon of extensor digitorum in between fourth and fifth digit in left hand

Department of Sharir Rachana, National Institute of Ayurveda, Jaipur, Rajasthan, India

Date of Submission10-Sep-2020
Date of Decision09-Dec-2020
Date of Acceptance12-Dec-2020
Date of Web Publication26-Mar-2021

Correspondence Address:
Rashi Sharma
4/36 J, G1, Sunrise Enclave, Chitrakoot, Vaishali Nagar, Jaipur - 302 021, Rajasthan
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/joa.joa_77_20

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Introduction: Tendon variation of Extensor Digitorum muscle was observed in a 48yr old male formalin fixed cadaver, during the dissection at Anatomy Dissection hall. The tendons of Extensor Digitorum muscle shows anatomical variation most often and its knowledge is important to assess the diseased and traumatized hand. Incidences have shown that tendons of ED may be variably deficient but more often they are doubled or even tripled in one or more digits. The incidences of doubling are higher in index finger or in the middle finger. Very rarely a slip of tendon passes to the thumb. Methods: Regular dissection at Anatomy Dissection Hall. Result & Conclusion: In this present case in left forearm, the origin of muscle was normal but its tendon divides into five proximal to wrist which pass through a common synovial sheath deep to the Extensor Retinaculum. The extra tendon is in between 4th and 5th digit. The right forearm does not show any anatomical variation. This type of variation is rarely found. This particular variation is important for clinical perspective. This case study is useful for surgeons performing Tendon Graft Operations or Tenoplasty.

Keywords: Anatomical variation, ED muscle, extensor digitorum, tendon graft operation, tenoplasty

How to cite this article:
Sharma R, Kumar S. A variation: An extra tendon of extensor digitorum in between fourth and fifth digit in left hand. J Ayurveda 2021;15:30-2

How to cite this URL:
Sharma R, Kumar S. A variation: An extra tendon of extensor digitorum in between fourth and fifth digit in left hand. J Ayurveda [serial online] 2021 [cited 2021 Apr 13];15:30-2. Available from: http://www.journayu.in/text.asp?2021/15/1/30/311921

  Introduction Top

Extensor digitorum (ED) muscle of the hand originates from the lateral epicondyle of the humerus. It is the principal extensor of medial four digits. It occupies much of the posterior surface of the forearm. Then, it divides distally into four tendons, which pass together with the tendon of the extensor indicis, through a separate tunnel under the extensor retinaculum in a common synovial sheath. The tendons then diverge on the dorsum of the hand, one to each finger. This muscle is supplied by posterior interosseous nerve (C7 and C8), a branch of the radial nerve.

On the dorsum of the hand, tendons spread out as they run toward the digits. Adjacent tendons are linked proximal to the knuckles (Metacarpophalangeal joints) by three variable intertendinous connections (juncture tendinae) which are inclined distally and radially. These intertendinous connections restrict independent extension of four medial digits[1] [Figure 1].
Figure 1: Represents the classically taught dorsal extensor digitorum anatomy

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On the distal ends of the metacarpals and along the phalanges of the four medial digits, the four tendons flatten to form extensor expansions. In forming the extensor expansion, each ED divides into a median band, which passes to the base of the middle phalanx and two lateral bands, which pass to the base of the distal phalanx.

Action of extensor digitorum muscle

ED extends all the joints through which it passes: Wrist, metacarpophalangeal, and through extensor expansion of digits, the proximal and distal interphalangeal joints. When acting on metacarpophalangeal joints, it tends to expand digits apart. It extends proximal phalanges and through its collateral reinforcements, the middle and distal phalanges as well. It also helps to extend the hand at the wrist joint after exerting its traction primarily on the digits.[1],[2]

Known variations

The tendons of ED may be variably deficient. More commonly they are doubled or even tripled in one or more digits (most often in the Index finger or in the middle finger).[3],[4] Occasionally, a slip of tendon passes to the thumb.[4]

  Materials and Methods Top

During routine dissection of the left upper limb of a formalin-fixed 48-year-old male cadaver, we came across variation in the ED tendon slips. An anomalous tendon slip between 4th and 5th digit is found.

  Case Report Top

An anatomical variation of the tendon of ED muscle was observed during dissection of a formalin-fixed male cadaver of about 48 years of age who died due to head injury in a road accident. The dissection was done in the dissection hall of the Anatomy department in National Institute of Ayurveda Jaipur. While dissecting the left posterior forearm and dorsum of the hand, as we reach in the middle of the posterior forearm we identified and clean the ED muscle. It distally splits into five tendons that pass deep to the extensor retinaculum to reach digits 2–5. The 5th extra tendon is in between 4th and 5th digit. There were five tendons of ED; the extra tendon splitting into two, close to the metacarpophalangeal joint and contributing to the tendons to the ring and little fingers. The extra tendon when reaches the distal end of the proximal phalanx it gives two collateral parts which insert onto the base of the middle phalanx of the ring finger and little finger. This type of variation is rarely found. The anomalous tendon was delineated and the specimen was photographed [Figure 2].
Figure 2: Represents left extensor surface of the forearm and hand showing tendons of ED along with anomalous tendon of ED between digit 4th and 5th. ED: Extensor digitorum

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  Discussion Top

Anomalies of muscles and tendons in the hand and wrist are significant during hand surgery. When found at random during operation, they are often neglected, but they are sometimes the cause of different syndromes in and around the wrist. From several studies,[5] we found that:

  • ED to the index finger-absent in 2% hand

    • With a single tendon in 90% hand
    • With double and triple tendons in 8%.

  • ED to middle finger-with single tendon in 72% hand

    • With double and triple tendons in 26% hand
    • With multiple tendons in 2% hand.

  • ED to ring finger-with single tendon in 44% hand

    • With double and triple tendons in 44% hand
    • With multiple tendons in 12% hand.

  • ED to little finger-with single tendon in 22% hand

    • With double tendons in 20% hand
    • No tendon in 58% hand.

However in this case, we found an extra single tendon in between 4th and 5th digits of the left hand only. Such type of variation is unique on its own.

  Result and Conclusion Top

The arrangement of the anomalous tendon of ED may increase the extension component of the ring finger and little finger. This case study might be useful for surgeons performing tendon graft operations. If a surgeon is completely aware of incidences of variation in ED he can perform well while transplanting extensor tendons.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Moore Keith L, Dalley Arthur F, Agur Anne MR. Clinically Oriented Anatomy. South Asian ed., Vol. 1. New Delhi: Wolter's Kluwer (India) Pvt. Ltd.; 2018.  Back to cited text no. 1
Snell Richard S. Clinical Anatomy by Regions. 9th ed. New Delhi Publ: Wolter's Kluwer (India) Pvt. Ltd.; 2015.  Back to cited text no. 2
Das S, Sulaiman IM, Hussan F, Latiff AA, Suhaimi FH, Othman F. The additional tendons of the extensor digitorum muscle of the hand: An anatomical study with a clinical significance. Bratisl Lek Listy 2008;109:584-6.  Back to cited text no. 3
Susan S. Gray's Anatomy; International Edition. 41st edition, Elsevier publication; 2016.  Back to cited text no. 4
Zilber S, Oberlin C. Anatomical variations of the extensor tendons to the fingers over the dorsum of the hand: A study of 50 hands and a review of the literature. Plast Reconstr Surg 2004;113:214-21.  Back to cited text no. 5


  [Figure 1], [Figure 2]


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