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How Do the Cervical Plexus and the Spinal Accessory Nerve Contribute to the Innervation of the Trapezius Muscle?
As Seen From Within Using Sihler's Stain
Antonius C. Kierner, MD;
Irmgard Zelenka, MD;
Martin Burian, MD
Arch Otolaryngol Head Neck Surg. 2001;127:1230-1232.
ABSTRACT
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Objective To determine how the spinal accessory nerve and the trapezius branches
of the cervical plexus contribute to the innervation of each of the 3 parts
of the trapezius muscle. Special emphasis was placed on the nerve supply of
the clinically most important descending part of the muscle.
Design Anatomical analysis of the distribution of the cervical plexus and spinal
accessory nerve branches in the human trapezius muscle.
Materials Twenty-two trapezius muscles from 11 perfusion-fixed human cadavers
ranging in age from 66 to 92 years (mean, 81.7 years).
Interventions The specimens were dissected free and macerated, decalcified, and stained
according to Sihler's technique for about 6 weeks. The translucent, stained
muscles were then backlit, and the findings were documented photographically
and by schematic drawings.
Results In all 22 muscles, the innervation of each of the 3 parts of the trapezius
muscle was seen. In all muscles investigated, the nerve supply to the descending
part of the muscle consisted of a single fine branch of the spinal accessory
nerve, whereas the transverse and ascending parts were innervated by both
the spinal accessory nerve and the trapezius branches of the cervical plexus.
Conclusion Our results, especially those involving the descending part of the trapezius
muscle, may help to minimize the rate of unexpected trapezius muscle paresis
after surgery of the neck.
INTRODUCTION
AS SHOWN IN a recent article,1 there
are more questions than answers concerning the innervation of the trapezius
muscle. Against the backdrop of a high rate of unexpected trapezius muscle
paresis after surgery of the neck, these questions still demand attention.2-5 For the
physician, the descending part of the trapezius muscle gains outstanding interest
because it maintains the stability of the shoulder girdle.6-9
Various sources of innervation to this muscle have been described.10-16
Apart from the majority of the statements on this question being purely speculative,
the data presented are often confusing or even contradictory. Since almost
all surgeons try to save the spinal accessory nerve (SAN) during modified
radical neck dissection, the high rate of unexpected trapezius muscle paresis
remains unclear. Until now, none of the hypotheses published on trapezius
muscle innervation could resolve this problem, perhaps partly because almost
all investigations dealing with this topic were based on either gross dissection
or electromyography, both of which have considerable limitations.12, 17 Thus, a final, reliable statement
on the innervation of each of the 3 parts of the trapezius muscle could not
be made on the basis of the results obtained by using these techniques.
Our aim was to elucidate how the branches of the cervical plexus and
the SAN contribute to the innervation of the 3 parts of the trapezius muscle.
The simple, reliable technique of Sihler,18
recently recalled by Wu and Sanders,19 was
used to stain nerve fibers while simultaneously making muscle tissue translucent.
MATERIALS AND METHODS
Twenty-two trapezius muscles were taken from 11 cadavers of both sexes
that ranged in age from 66 to 92 years (mean, 81.7 years) and had been donated
to the Institute of Anatomy 2, University of Vienna, Austria. The nerves passing
into the muscles, ie, the SAN and trapezius branches of the cervical plexus,
were identified and marked with a colored thread before the muscles were dissected
free on both sides. The muscles were fixed for at least 6 weeks in 4% paraformaldehyde
buffered with 0.1M phosphate buffer to pH 7.4 and then stained according to
the modified method of Sihler18 as described
by Wu and Sanders,19 as follows:
- The fixed specimens were macerated in a solution containing 4
mL of 3% hydrogen peroxide and 2000 mL of 3% potassium hydroxide for approximately
3 weeks.
- The macerated specimens were decalcified by immersion in a combination
of 250 mL of glacial acetic acid, 250 mL of 100% glycerin, and 1500 mL of
1% aqueous chloral hydrate (solution 1) for 2 to 4 weeks.
- The decalcified specimens were then stained by immersion in a
combination of 250 mL of Ehrlich's acid hematoxylin, 250 mL of 100% glycerin,
and 1500 mL of 1% aqueous chloral hydrate (solution 2) for 2 to 3 weeks.
- After staining, the specimens were again transferred to solution
1 for approximately 6 hours.
- For neutralization, the specimens were then immersed in 0.05%
lithium carbonate for approximately 1 hour.
- Finally, the specimens were immersed in increasing concentrations
of glycerin daily and preserved in 100% glycerin with a few thymol crystals
(day 1, 30%; day 2, 50%; day 3, 60%; day 4, 70%; day 5, 80%; and day 6, 100%
plus thymol).
Subsequently, all muscles were pressed between 2 glass planes. The specimens
were backlit, and the exact number and topography of all nerves passing into
or running through each muscle were recorded. All representative cases were
photographed.
RESULTS
The SAN and the trapezius branches of the cervical plexus merged on
the ventral surface of the transverse part of the trapezius muscle, or a little
caudal to that, in all 22 specimens (Figure
1 and Figure 2). Thus,
the SAN and cervical plexus branches also passed into the same parts of the
muscle in all specimens (Figure 2 and Figure 3).
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Figure 1. Schematic illustration of the
trapezius muscle innervation. Note the fine branch of the spinal accessory
nerve (SAN) (top arrow), which could be found in all 22 specimens investigated.
The solid circle (bottom arrow) indicates the approximate point where the
SAN and the trapezius branches (dashed lines) of the cervical plexus (rami
trapezii) merge, which occurred in all 22 specimens.
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Figure 2. Right trapezius muscle stained
according to Sihler's technique. The open arrowhead indicates the spinal accessory
nerve (SAN); the solid arrowhead, the branch of the SAN passing into the descending
part of the muscle; the long fine arrow, the trapezius branches of the cervical
plexus; and the short fine arrows, the cutaneous nerves arising from the posterior
divisions of the dorsal nerves (so-called segmental branches) passing through
the muscle.
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Figure 3. Enlargement of the descending
part of a right trapezius muscle. The arrows indicate the branch of the spinal
accessory nerve passing into the descending part of the trapezius muscle.
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In all specimens, 1 to 8 (mean, 7.3) dorsal cutaneous branches were
found. These segmental branches always passed through the tendinous plane,
from which the muscle takes its origin; none of them branched inside the trapezius
muscle (Figure 2).
A single fine branch of the SAN passing to the descending part of the
trapezius muscle, as recently described in a cross-dissection study,1 was found in all 22 muscles investigated (Figure 1, Figure 2, and Figure 3).
No anastomoses were found between this branch and the nerves passing into
the muscle more caudally. No other nerve was detected passing into the descending
part of the trapezius muscle (Figure 2).
COMMENT
As far as we know, this is the first study showing that the SAN and
the trapezius branches of the cervical plexus merge and pass together to the
transverse as well as to the ascending part of the trapezius muscle (Figure 1 and Figure 2). The descending part of the muscle, however, is innervated
solely by a single fine branch of the SAN (Figure 2 and Figure 3).
Furthermore, we showed that the so-called segmental branches do not branch
within the trapezius muscle and are obviously identical to the cutaneous nerves
arising from the posterior divisions of the cervical nerves, which are thought
to be purely afferent. Beside the well-known innervation of the trapezius
muscle by the SAN and the rami trapezii of the cervical plexus, no other nerve
supply could be found. This contrasts with the findings of Soo et al,15 Krause et al,16, 20
and Niemeyer and Ludolph.13 Furthermore, we
could not detect any branches, other than the one arising from the SAN, passing
toward the descending part of the muscle and indicating a dual innervation
as stated by Krause et al.21 However, a purely
cervical innervation of the descending part, as suggested by Haas and Sollberg,7 seems even more unusual and has never been proven.
On the basis of more recent work by Karuman and Soo22
and our own findings, we strongly disagree with the statement by Weitz et
al23 that the whole trapezius muscle has a
dual innervation and the surgical consequences they propose. On the other
hand, as early as 1974, Fahrer et al11 pointed
out that, based on their clinical experience, a purely cervical supply to
the upper part of the trapezius muscle as suggested by Rosenstein24 could not be accepted as a rule, and Fahrer et al
could find no evidence that the trapezius muscle can be supplied by cervical
fibers only.
It must be stressed that the previous studies mentioned are all based
on clinical experience, gross dissection, and/or electromyography, which leaves
a shade of doubt on the reliability of their findings.
Since the branch of the SAN passing to the descending part of the trapezius
muscle was the only nerve found in this part of the muscle, we believe that
it is a mixed nerve. Nonetheless, this important chapter on the innervation
of the trapezius muscle still cannot be closed.
In conclusion, although our findings regarding the innervation of the
descending part of the trapezius muscle have yet to be proven in clinical
practice, we are convinced that they can help minimize the rate of unexpected
trapezius muscle paresis after surgery of the neck.
AUTHOR INFORMATION
Accepted for publication May 16, 2001.
Corresponding author and reprints: Antonius C. Kierner, MD, Schwanheimerstr
3, D-60 528 Frankfurt a.M., Germany (e-mail: kierner{at}em.uni-frankfurt.de).
From the Ear, Nose, and Throat Department, University Hospital Vienna
(Drs Kierner and Burian), and the Institute of Anatomy 2, University of Vienna
(Dr Zelenka), Vienna, Austria. Dr Kierner is now with the Ear, Nose, and Throat
Department, University of Frankfurt, Frankfurt a.M., Germany.
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