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Case Report
Anatomical
Variations in the Extensor Digiti Minimi Tendon: A Case Study and Significance
Mohammed A. A.
Abdelmotalab٭1, Mohamed O. Mustafa2
Abstract:
Background: Anatomical variations of muscle tendons are usually benign, but they may impact various clinical aspects.
Case description: On dissection of a formaldehyde 65-year male cadaver’s upper extremities, the extensor digiti minimi tendon of the right hand exhibited double slips crossing deep to the extensor retinaculum joining dorsal digital expansion of the little finger. In contrast, the left-hand muscle presented with one tendon. Literature review showed that such variations are not uncommon and may explain symptoms related to pain and/or swellings on the dorsum of the hand. Awareness of students and surgeons to such variations may have clinical significance.
Conclusion: Explanation of variations encountered during the laboratory dissection should be discussed among the students to maximize their knowledge about variations and their possible clinical significance.
Keywords: Anatomical variations, Tendon, Extensor digiti minimi
___________________________________________________________
1Anatomy Department, Faculty of Medicine, International University of Africa, khartoum, Sudan.2Anatomy Department, Faculty of Medicine, University of Gadarif, Sudan.
٭Corresponding Author: Mohammed Abduaslam Ahmed Abdelmotalab, Department of Anatomy, International University of Africa
Email: salam_ahamed@yahoo.com
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:Introduction
The extensor digiti minimi (EDM) muscle arises from the lateral epicondyle of the humorous and then joins the dorsal extensor expansion of the little finger, innervated by deep branches of the radial nerve C7 and C8. The muscle acts to extend the metacarpal phalangeal joint of the little finger.(1) Normally, the EDM is a fusiform slip of muscle partially detached from the extensor digitorum muscle. Its tendon then divides into two slips: the lateral one joined to the tendon of the extensor digitorum, with all three tendons attaching to the dorsal digital expansion of the little finger. After exerting its traction primarily on the 5th finger, it contributes to the extension of the hand.(2)
Variations in muscles and tendons are usually of academic interest. However, such variations may cause symptoms that maybe difficult to distinguish from soft tissue tumours and may lead to surgical complications. There are reported examples of clinically relevant anatomical variations identified in many medical schools where the students found them not in concordance with classical anatomical teaching.(3,4)
In this case study we describe our experience with unusual anatomical relations of
. the EDM muscle and discuss the clinical significance of these findings
:Case description
These were observations noted during the dissection of the upper extremities of a formaldehyde 65-year male cadaver in the Department of Human Anatomy, Faculty of Medicine, National University, during the academic year 2016-2017. The dissection was done according to the guides of Cunningham’s Manual of Practical Anatomy. The process started by removing the skin of the dorsum of the hand,
. excising the fasciae carefully and preserving the underlying
tendons, examined and followed to their destination in dorsal digital expansion. The EDM tendon of the right hand exhibited double slips crossing deep to the extensor retinaculum to share the formation of the dorsal digital expansion of the little finger with the tendon originating from the extensor digitorum. In contrast, the left-hand muscle presented with one tendon. There were no other variations
. noted in the extensor tendons of the hands
.Figures (1 and 2)
Figure (2). The posterior compartment of the forearm and the dorsum of the right hand shows the extensor digiti minimi (EDM) tendon before splitting in double slips (1 and 2) distal to the extensor retinaculum and extensor
. digitorum (ED) muscle
:Discussion
Normally, the EDM muscle has double tendons that are separate from the tendons of the extensor digitorum muscle.(5)
Anatomical variations may sometimes be observed. In the current study, the EDM tendon of the right hand exhibited two slips after crossing the extensor retinaculum muscle, joining the dorsal digital expansion of the little finger. In contrast, the left-hand muscle presented with one slip. This result is compared to the literature reported by other researchers. In one such report, the EDM was found to have three tendons: two tendons to the little finger and one to the ring finger metacarpophalangeal joint.(6) The ring finger slip was inserted in the extensor hood with the extensor digitorum communis (EDC). The EDC had a separate tendon to the little finger. The metacarpophalangeal joints of the little and ring fingers extended simultaneous contraction of the EDM or the EDC.(6) A study of the extensor tendons and their communications were analyzed in 50 cadaveric hands. The common distribution showed that the EDM presented with two tendons; however, a tendon slip from the EDM to the ring finger was observed in one hand.(7) This is similar to the findings in our case study, where the tendon of EDM of the right hand was presented with splitting into two slips, while the left digiti minimi tendon didn’t show the same feature. The other extensor tendons had normal anatomical distributions toward their insertions.(7)
A study of 181 dissected hands showed that EDM had two tendons in most cases. It was always connected to the extensor digitorum either by receiving one or part of its tendon or by tendonous connections.(8) In another study, the EDM was observed to have five slips on the right hand; extending to radial slip, ulnar slip, the middle finger, the ring finger and the little finger.(9)
In a study of the frequency of variations of EDM tendons in 50 dissected hands, the tendons were absent in one hand (2%), there was a single tendon in nine (18%), double tendons in 35 (70%) and triple tendons in five (10%).(10)
It has been reported that the EDM usually has two tendons, but may have three or four.(11) In addition to EDM, the little finger receives either a separate tendon or a tendinous slip from the extensor digitorum.(11) In summary, the previous studies show that the EDM tendon had double slips in most cases. However, in some instances, there
. were up to five slips and it was rare to be absent
:Clinical implications
The variations of the hand extensor tendons are common, mostly asymptomatic, some may interfere with and occupy the narrow dorsal compartments of the wrist, causing pain in the dorsal wrist and affecting digital movement.(12)An example was a thirty-year-old subject who had multiple slips of the EDM causing a bulbous appearance.(12) In another clinical case report, a 21-year-old woman presented with swelling and pain during flexion of the wrist joint at the dorsal side of the ulna. Surgical exploration revealed additional radial slip from the EDM tendon. The extensor retinaculum was released and the smaller slip of the EDM was removed. Histopathological examination revealed tenosynovitis.(13) Surgeons need to be mindful of anatomical variations when operating for tendon transferring in the wrist and dorsal surface of the hand.(14)
Variations in EDM and other extensor tendons have clinical implications in reconstruction surgery. The additional tendons can be used for grafting instead of the main tendons. Another value is the interpretation of symptoms during trauma or excessive wrist movements. Thus, it is of paramount importance for surgeons to
. be aware of these variations and to scrutinize these tendons
:Conclusion
In this case study, the right EDM tendon was noted to have double slips joining the dorsal digital expansion separately. Anatomical variations should be studied and explained to students when present and their clinical significance discussed. Anatomists and surgeons should report all the variations for better knowledge of
. human anatomy
:Acknowledgement
Sincere gratitude is extended to the director of the National University and the team of the Department of Anatomy for their invaluable cooperation throughout
. the work conduction
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