Extensor carpi ulnaris - IJAV • International Journal of Anatomical

eISSN 1308-4038
International Journal of Anatomical Variations (2013) 6: 231–233
Case Report
Extensor carpi ulnaris: bilateral accessory tendons to the fifth metacarpal
Published online December 28th, 2013 © http://www.ijav.org
Zailene D. FLOOD
Dustin J. HAWLEY
Mia C. MARSHALL
Anthony A. CAPEHART
Department of Biology, East Carolina University, Greenville,
NC, USA.
Anthony A. Capehart, PhD
Professor
Department of Biology
East Carolina University
Greenville, NC 27858, USA.
+1 (252) 328-6296
[email protected]
Received January 17th, 2013; accepted March 29th, 2013
Abstract
We report bilateral accessory tendons discovered during routine anatomical dissection that
originated from the extensor carpi ulnaris and inserted into the 5th metacarpals. The left
variant arose from the tendon of extensor carpi ulnaris under the extensor retinaculum and
passed superficial to insertion of its primary tendon to reach the medial side of the head of the
5th metacarpal separate from extensor digiti minimi. The right variant, however, originated from
a small 2 cm muscular slip of extensor carpi ulnaris close to origin of its primary tendon in the
mid-forearm. This accessory tendon was 16 cm in length and traveled alongside that of extensor
carpi ulnaris. In its course across the dorsum of the hand, this variant also passed superficial to
insertion of extensor carpi ulnaris and inserted on the 5th metacarpal head to the medial side of
extensor digiti minimi.
© Int J Anat Var (IJAV). 2013; 6: 231–233.
Key words [extensor carpi ulnaris] [extensor digiti minimi] [anatomical variation]
Introduction
Case Report
Awareness of potential variations in muscular organization
and routing of tendinous insertions is essential for those
in medical education, practice, and research. In the upper
limb the extensor carpi ulnaris muscle originates from the
lateral epicondyle of the humerus by the common extensor
tendon and from the posterior aspect of the proximal half
of the ulna to insert on the base of the 5th metacarpal [1].
Several interesting reports of accessory tendon slips arising
from extensor carpi ulnaris have been documented, most of
which describe variants that arise at the level of the wrist or
dorsum of the hand [2–5]. As indicated recently [6], additional
studies of accessory tendon slips associated with extensor
carpi ulnaris in different populations are needed to ascertain
potential extent of variation that may occur in this important
muscle of the extensor compartment. We describe an unusual
case in which bilateral accessory tendons of extensor carpi
ulnaris occurred; the left accessory tendon was of short
length similar to aforementioned variants, but on the right
it originated from the muscle belly in the mid-forearm. Both
variants passed across the dorsum of the hand to insert on
the head of the 5th metacarpal medial to and separate from
extensor digiti minimi.
Bilateral occurrence of variant tendons arising from
extensor carpi ulnaris was observed in an elderly Caucasian
female cadaver during routine dissection and preparation
of specimens for nursing and allied health anatomy
laboratories.
In the left upper limb, the tendon variant was identified as it
crossed the dorsum of the hand, medial and parallel to the
tendon of extensor digiti minimi (Figure 1a). Upon reflection
of the extensor retinaculum it was noted that this 8.5 cm slip
arose directly from the dorsal aspect of the extensor carpi
ulnaris tendon, shared the 6th extensor compartment, and
in its course crossed over the insertion of extensor carpi
ulnaris (Figure 1b). The accessory tendon was 1 mm in width,
consistent in this dimension, and inserted on the head of the
5th metacarpal medial to and separate from extensor digiti
minimi. Some terminal fibers blended with the proximal
extensor expansion along its medial aspect.
As shown in Figure 2a, the right tendon variant arose from a
small muscle slip located on the lateral aspect of extensor carpi
ulnaris 14 cm distal to its origin from the lateral epicondyle.
This 2 cm muscular slip was located near the origin of the
muscle’s primary tendon. The tendon variant was 2 mm
wide and closely accompanied the tendon of extensor carpi
ulnaris on its lateral side, consistent in width throughout
Flood et al.
232
the majority of its course. The accessory tendon was 16
cm in length, passed over insertion of the primary tendon
of extensor carpi ulnaris (Figure 2b) and traveled straight
across the dorsum of the hand, similar to the path noted in
the contralateral limb. The right variant tendon increased
to 7 mm in width as it approached the metacarpophalangeal
joint and inserted into the head of the 5th metacarpal. Fibers
from this distal expansion blended into the proximal aspect of
the extensor hood separate from insertion of extensor digiti
minimi (Figure 2c).
The extensor digiti minimi tendon was not duplicated on the
right hand (Figures 2b, c) and on the left exhibited only a bifid
appearance immediately proximal to its insertion (Figure 1b).
Juncturae tendinum interconnected extensor digiti minimi to
the extensor digitorum tendon servicing the 4th digit in both
instances (Figures 1b, 2b, c). This fascial band was notably
robust on the right side, measuring 1 cm in width.
b
a
ECU
ECU
a
b
ED
ECU
ECU
ED
EDM
*
EDM
Var
Var
*
3
4
5
Figure 1. Photographs of the left upper limb illustrating the
accessory tendon from extensor carpi ulnaris (ECU). a) Overview of
forearm anatomy showing the variant tendon (Var) on dorsum of the
hand. (Asterisk: extensor retinaculum; large arrowhead: extensor
digiti minimi tendon) b) Closer view of variant tendon origin (small
arrowhead) and route superficial to extensor carpi ulnaris insertion
(large arrowhead), ending on the 5th metacarpal head. Note bifid
insertion of extensor digiti minimi tendon (EDM) and junctura
tendinum to extensor digitorum (ED) digit 4 tendon (asterisk).
EDM
ED
Var
*
5
4 3
ED
ECU
EDM
Discussion
Several reports of unilateral extensor carpi ulnaris tendon
variation have been documented with differing frequency
ED
Var
EDM
Var
c
*
5
4
3
Figure 2. Photographs of right forearm demonstrating the accessory
tendon from extensor carpi ulnaris (ECU). a) Origin (arrowhead) of
tendon variant (Var) and path to the wrist alongside the primary
tendon of extensor carpi ulnaris. b, c) Course of variant tendon on
dorsum of wrist and hand passing superficial to insertion of extensor
carpi ulnaris to end on the 5th metacarpal head. Note expansion of
accessory tendon at insertion and separate insertion of extensor
digiti minimi (EDM) tendon with prominent junctura tendinum
joining tendon of extensor digitorum (ED) to digit 4 (asterisk).
among populations examined. In Nakashima’s classic study [3],
the Type C accessory tendon inserted into the 5th metacarpal
head and was the least frequent of variants described,
occurring in 1.7% of cases. A similar insertion was noted in
5.6-14.8% of variants from different populations [2, 4, 6].
Herein we report an unusual case in which there was bilateral
extensor carpi ulnaris tendon variation with the Type C
insertion [3]. To our knowledge this is the first report of
duplication of this specific tendinous variation in the same
individual. Origin of the left tendon was like that described
by Nakashima [3] in that it arose from the primary tendon of
extensor carpi ulnaris within the 6th extensor compartment
and inserted on the 5th metacarpal head, medial and separate
from extensor digiti minimi. Its width (1 mm) was the same
as described previously [5]. In the right extremity, however,
the variant had a proximal origin directly from a small lateral
muscular slip associated with the belly of extensor carpi
ulnaris. While there has been report of the variant tendon
arising proximal to the 6th compartment sheath [4], few
have documented its origin from the heads of extensor carpi
ulnaris [6] or elsewhere along the muscle belly, indicating
that this may be a rare occurrence. In the present case the
width of the right variant slip (2 mm) was slightly larger, but
Variant extensor carpi ulnaris tendons
similar to that reported previously [3]. Its insertion into the
5th metacarpal was like that of the contralateral extremity
with the exception that the right accessory tendon exhibited
a notable expansion in width just proximal to insertion that
permitted greater association with fibers of the proximal
extensor apparatus. As in the left hand, the variant remained
medial to and separate from insertion of extensor digiti
minimi.
In a recent large study [7], it should also be noted that most
tendons of the extensor digiti minimi were duplicated,
remaining single at insertion in only 20% of cases. In the
present instance, a single tendon of extensor digiti minimi
on the right was present and on the left, split into 2 short
adjacent slips just before insertion. It is unknown whether
presence of the additional tendon slips from extensor carpi
ulnaris impacted extensor digiti minimi tendon structure
and lessened an overall need for duplication; however, it is
233
interesting that duplication of the extensor digiti minimi
tendon often resulted in medial and lateral slips that insert
separately [7], similar to the relationship of digit 5 tendons
noted in the present report. The juncturae tendinum between
extensor digitorum and extensor digiti minimi could
potentially offset single tendon weakness [8].
Little is known of mechanisms that govern limb tendon
morphogenesis although ectodermal signals appear essential
for induction [9]. Misexpression of scleraxis and other
regulators of tenocyte differentiation may perhaps result in
variants such as described here. Accessory slips of extensor
carpi ulnaris that do occur and insert on the 5th metacarpal
head can have clinical significance in wrist/digit function or
may be utilized for tendon graft [6]. Accessory extensor carpi
ulnaris tendons have been documented in all populations
examined and extent of this variation should be considered
during development of surgical strategies for the hand.
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