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A cadaveric study of the serratus anterior muscle and the long
thoracic nerve
Junichiro Hamada, MD, PhD,
a
Emi Igarashi, RPT,
b
Keiichi Akita, MD, PhD,
c
and Tomoyuki Mochizuki, MD, PhD,
d
Koriyama and Tokyo, Japan
The anatomy and function of the serratus anterior muscle
and the long thoracic nerve have not been fully
elucidated. The purposes of this investigation were (1) to
clarify which nerve roots of the cervical spine supply each
part of the muscle and contribute to the long thoracic
nerve and (2) to investigate the anatomy of the 3 parts of
the muscle to understand the function of each part. We
collected specimens from 70 dissections of 35 cadavers
(11 men and 24 women). The serratus anterior muscle
consisted of the upper, middle, and lower parts. The
upper part was supplied mainly by the C5 nerve root,
and the C4, C6, or C7 nerve roots also had multiple
branches in 64 of 70 dissections. The long thoracic
nerve, consisting of the C6 and C7 nerve roots,
innervated the middle and lower parts. The upper part
traversed in a posterior direction compared with the
middle or lower part. The upper part of the muscle, which
is supplied from multiple nerve roots and runs in
a posterior direction, may stabilize the rotational motion
of the scapula on the thorax in shoulder elevation. The
middle part provides the scapular abduction, and the
lower part contributes to upward rotation, abduction,
and posterior tilting. (J Shoulder Elbow Surg
2008;17:790-794.)
The serratus anterior muscle, which plays an essential
role in shoulder function, has a distinctive role in evolu-
tion, is of practical interest to the clinician, and is one of
the most important muscles of the body. The serratus an-
terior muscle, in conjunction with the trapezius, func-
tions principally as a scapular upward rotator during
elevation of the shoulder.
4,12
Without the action of
the serratus anterior, scapular rotation is markedly re-
stricted and arm elevation is limited to about 90.
3
Therefore, the serratus anterior is unique among the
scapulothoracic muscles in having the ability to con-
tribute to all components of the normal 3-dimensional
movement of the scapula on the thorax during eleva-
tion of the shoulder.
16
Specifically, this muscle can pro-
duce upward rotation, abduction, posterior tilting, and
internal rotation of the scapula while stabilizing the
medial border and inferior angle of the scapula to
the thoracic wall, preventing scapular winging.
15,16
The importance of the serratus anterior is further sup-
ported by the presence of abnormal muscle activation
in various shoulder pathologies. Reduced serratus
anterior electromyographic activity has been demon-
strated in throwers with glenohumeral instability,
7
con-
struction workers with subacromial impingement,
17
and swimmers with shoulder pain.
19
Moreover, 2
main causes have been proposed for isolated paralysis
of the serratus anterior due to long thoracic nerve
palsy. Some authors include it in the general condition
known as neuralgic amyotrophy.
6
Others attribute this
phenomenon to entrapment neuropathy or nerve in-
jury being involved in sports, repetitive work, an auto-
mobile accident, trauma, or surgery.
8,9,11,14,20
On the basis of muscle fiber origin, direction, and
insertion, the serratus anterior has been divided into
3 major parts. Eisler
5
classified the serratus anterior
muscle into 3 parts: the upper part, arising from the
first and second ribs attached to the superior angle
of the scapula; the middle part, originating from the
second and third ribs attached to the medial border
of the scapula; and the lower part, arising from under
the fourth ribs attached to the inferior angle. Each
part of the serratus anterior may exhibit different func-
tions and different nerve root supplies. Gregg et al
9
proposed that the upper part was responsible for scap-
ular rotation whereas the middle part was involved in
scapula protraction. However, Bertelli and Ghizoni
2
stated that the upper part was responsible for scapula
protraction and the lower part, with its fan shape, was
the more important for scapula stabilization. Hence,
the specific functions of each component in the muscle
and nerve supplies remain controversial.
The long thoracic nerve is a motor nerve innervat-
ing the serratus anterior, typically arising from the
From the Departments of
a
Orthopedics and
b
Physical Therapy,
Kuwano Kyoritsu Hospital, Koriyama
c
Unit of Clinical Anatomy;
and
d
Section of Orthopedic Surgery, Graduate School, Tokyo
Medical and Dental University, Tokyo.
Reprint requests: Junichiro Hamada, MD, PhD, Department of
Orthopedic Surgery, Kuwano Kyoritsu Hospital, 2-9-18 Shima,
Koriyama, Fukushima 963-8034, Japan (E-mail: i-hamada@
koriyama-h-coop.or.jp).
Copyright ª2008 by Journal of Shoulder and Elbow Surgery
Board of Trustees.
1058-2746/2008/$34.00
doi:10.1016/j.jse.2008.02.009
790
C5, C6, and C7 cervical nerve roots. Horwitz and
Tocantins
11
dissected the nerve in 100 specimens
from 50 cadavers and described the typical anatomic
arrangement, in which the C5 and C6 branches
pierce the scalenus medius muscle. These 2 branches
unite shortly after exiting the scalenus medius and join
with the C7 branch before descending the thoracic
wall. The only muscle supplied by the long thoracic
nerve is the serratus anterior. Spasms and rupture of
the scalenus medius have been considered as possible
etiologies of long thoracic nerve palsy.
11
In addition,
the nerve, which angulates over the second rib, large
muscular digitations medially, and the coracoid pro-
cess laterally, is susceptible to compression when lat-
eral pressure is exerted against the scapula.
11,20
Hester et al
10
described a tight fascial band of tissue
arising from the inferior aspect of the brachial plexus,
extending just superior to the scalenus medius inser-
tion on the first rib, and having digitations that
extended to the proximal aspect of the serratus ante-
rior. They also added that, with progressive manual
abduction and external rotation, the long thoracic
nerve was found to bowstring across the fascial
band. Therefore, 3 critical entrapment points for the
long thoracic nerve have been shown in the literature,
as described previously. The anatomy and function of
the serratus anterior muscle and the long thoracic
nerve have not been fully elucidated. The purposes
of this investigation were to clarify the function and
nerve root supply of each part of the serratus anterior
muscle and to elucidate the critical point for long tho-
racic nerve injury based on the anatomic structure.
MATERIALS AND METHODS
We collected 70 shoulders from 35 adult Japanese ca-
davers (11 men and 24 women; mean age, 82 years) for
this study. All cadavers were fixed in 8% formalin and pre-
served in 30% alcohol. To examine the origin, insertions,
and innervation of the serratus anterior, the rhomboids,
and the levator scapulae minutely, we removed the scapula
at its medial border after removal of the trapezius and latis-
simus dorsi muscles.
We investigated the origins, insertions, shapes, and di-
rection of the upper, middle, and lower parts of the serratus
anterior muscle according to the definition established by
Eisler.
5
Moreover, we dissected each cervical nerve root
and investigated which roots contributed to the long thoracic
nerve and its trajectory, whether the C5 and C6 branches
run in the substance of the scalenus medius, and the
branches innervating each part of the serratus anterior mus-
cle, and we observed 3 critical points, which have been de-
scribed in the literature for long thoracic nerve palsy,
carefully in 70 shoulders.
RESULTS
The upper and lower parts of the serratus anterior
muscle attached to the superior and inferior angles
of the scapula, respectively. Attachment of the upper
part was spread from the anterior side of the superior
angle to the dorsal surface. The middle part was at-
tached longitudinally to the medial border of the scap-
ula (Figure 1). Each part of the serratus anterior muscle
had 3 layers in a transverse plane; the upper part was
located more dorsal than the middle part; and the mid-
dle part was situated more dorsal than the lower part.
The upper part traversed in a posterior direction and
was characterized by a short length and wide section
(Figures 2 and 3). The middle part coursed posterome-
dially from the second and third ribs to the medial
border. The lower part, with its fan shape, formed
a convergent trajectory to the lower scapula angle.
Branches arising from the C5, C6, and C7 nerve
roots formed the long thoracic nerve in 61 of 70 dis-
sections, and the nerve included a contribution from
the C4 nerve root in 9. However, we were not able
to identify a branch from the C8 nerve root to the
long thoracic nerve. The branch of the C5 nerve root
originated together with the motor branch to the rhom-
boid muscle at the base of the brachial plexus and
passed through the scalenus medius (Figure 4). Perfo-
ration of cervical roots into the scalenus medius was
frequently observed, with C5 nerve root penetration
in 46 of 70 dissections (65.7%), C5 and C6 in 17
Figure 1 The serratus anterior muscle is composed of 3 parts. The
upper part (UP) is raised from the first and second ribs and attached
to the superior angle of the scapula, the middle part (MP) arises from
the second and third ribs and attaches to the medial border of the
scapula, and the lower part (LP) arises from under the fourth ribs
and attaches to the inferior angle.
J Shoulder Elbow Surg Hamada et al 791
Volume 17, Number 5
of 70 (24.3%), and C6 in 1 of 70 (1.4%). We did not
observe penetration of the C7 branch through the sca-
lenus medius and noted symmetric penetration in 26
of 35 cadavers (74.3%).
We observed 3 critical points where the long tho-
racic nerve was stretched or entrapped. Although
a tight fascial band of tissue has been reported to arise
from the inferior aspect of the brachial plexus and ex-
tend just superior to the scalenus medius muscle inser-
tion on the first rib, we did not observe such a band
(Figures 1 and 2). The penetration of the C5 and C6
branches through the scalenus medius has already
been mentioned previously.The final entrapment point,
angulation of the long thoracic nerve over the second
rib, could not be confirmed, because the second rib
was covered by the upper part of the serratus anterior
muscle as a soft-tissue floor to the nerve (Figure 2).
We summarized the nerve roots supplying each
part of the serratus anterior muscle in Table I. In at least
6 dissections, only the C5 contribution, supplying the
upper part, was identified. On the other hand, the C4,
C6, or C7 branch innervated the upper part in the re-
maining 64 dissections (C6 in 47 dissections, C7 in
19, and C4 in 9). The important finding that multiple
nerve roots supplied the upper part of the serratus an-
terior muscle emerged as a result of the investigation.
The C5 nerve root, which supplied the upper part, also
Figure 2 Anatomy of upper part (UP) and long thoracic nerve (LT N).
The upper part of the serratus anterior muscle, a large and powerful
mass, cylindrical in shape, is raised from the first and second ribs.
The long thoracic nerve runs over the upper part, which covers as
a soft tissue to the second rib. SSC, Subscapularis muscle; Superior
angle, superior angle of scapula.
Figure 3 Direction of upper part (UP) and middle part (MP). The up-
per part pulls the superior angle of the scapula anteriorly toward the
ribs, and the middle part pulls the medial border of the scapula ante-
rolaterally.
Figure 4 Penetration of branch of C5 nerve root into scalenus med-
ius (SM) muscle. The branch of the C5 nerve root passed through the
scalenus medius in 6 dissections. Branches of C6 and C7 communi-
cate to the branch of the C5 nerve root and form the long thoracic
nerve (LTN).
Table I Innervated nerve roots to each part of serratus anterior
Part of SA
Innervated
nerve roots
No. of
dissections
Upper part C5, C6 39 (55.7%)
C5, C6, C7 16 (22.9%)
C5 6 (8.6%)
C4, C5, C6 5 (7.1%)
C4, C5, C6, C7 3 (4.3%)
C4, C5 1 (1.4%)
Middle and lower part C6, C7 49 (70%)
C5, C6, C7 20 (28.6%)
C4, C5, C6, C7 1 (1.4%)
SA, Serratus anterior muscle.
792 Hamada et al J Shoulder Elbow Surg
September/October 2008
innervated both the elevator scapulae and rhomboi-
deus muscles in 63 dissections (Figure 5). The middle
and lower parts of the muscle were supplied from C6
and C7 in 49 dissections; C5, C6, and C7 in 20; and
C4, C5, C6, and C7 in 1 (Table I). Asymmetry of inner-
vations to each part was found in most cadavers.
DISCUSSION
When we elevate the arm, the scapula moves via
upward rotation, abduction, and posterior tilting be-
cause of the work of the serratus anterior muscle.
The superior angle of the scapula moves inferome-
dially by 1 cm and, through the inferior angle, trans-
versely by 10 cm on scapula plane elevation of the
arm according to our cineradiographic study (data
not shown). We speculate that the upper part of the
serratus anterior muscle, which is a large and power-
ful mass, cylindrical in shape, and runs in a posterior
direction, provides stabilization of the superior angle
of the scapula. Moreover, the upper part may cooper-
ate with the levator scapulae and rhomboid muscles to
control the motion of the medial boarder of the scap-
ula. The middle part provides the scapular abduction
from the direction of the muscle fiber. The lower part
provides scapular abduction and upward rotation in
coordination with the upper trapezius muscle. Gregg
et al
9
proposed that the upper part was a necessary
anchor that allowed the tremendous rotation required
to lift the arm, the middle part helped to draw the scap-
ula forward, and the lower part rotated the inferior
angle of the scapula upward and laterally across the
chest wall. We concur entirely with this opinion. In
contrast, Bertelli and Ghizoni
2
stated that the upper
part was responsible for scapular protraction and
the lower part was critical for scapular stabilization.
The upper part, running in a posterior direction, could
not contribute to scapular protraction, because the
middle part itself coursed posteromedially and trans-
versely and is responsible for abduction of the scap-
ula. When the long thoracic nerve is injured in the
axilla, or in the case of C7 nerve root disturbance,
the lower part of the serratus anterior muscle is dener-
vated and scapular winging is observed.
18
In this con-
text, we agree with the statement of Bertelli and
Ghizoni
2
that the lower part stabilizes the inferior an-
gle and inhibits winging of the scapula.
Our study showed that branches arising from the
C5, C6, and C7 nerve roots formed the long thoracic
nerve in 61 dissections and that the nerve included
a contribution from the C4 nerve root in 9. However,
we were not able to identify a branch from the C8
nerve root to the long thoracic nerve. This is probably
because of the limited number of dissections in our in-
vestigation. In a study of 73 dissections, Kato and
Sato
13
found that the C5, C6, and C7 nerve roots
formed the long thoracic nerve in 75% whereas the
C4 and C8 nerve roots contributed to the nerve in 4
and 7 dissections, respectively. Horwitz and Tocan-
tins
11
stated that the nerve was formed by the union
of branches from the C5, C6, and C7 nerve roots in
84 of 100 dissections; that the branch from C7 was
Figure 5 Example of nerve innervation pattern of 3 muscles. In the right serratus anterior (SA), the branch from only
the C5 nerve root innervates the upper part and branches from the C6 and C7 nerve roots reach both the middle and
lower parts. Hence, branches from the C5 and C6 nerve roots supply the left upper part, and branches from the C6
and C7 nerve roots reach the left middle and lower parts. The dorsal scapular nerve (a branch from the C5 nerve root)
supplying the rhomboids also passes through the scalenus medius. LS, Levator scapulae; R major, rhomboideus
major; R minor, rhomboideus minor.
J Shoulder Elbow Surg Hamada et al 793
Volume 17, Number 5
absent in 8%; and that the C5, C6, C7, and C8 nerve
roots contributed to the nerve in another 8%. Bertelli
and Ghizoni
2
demonstrated a branch from the C4
nerve root to the long thoracic nerve in 1 of 15 dissec-
tions. Therefore, branches arising from the C5, C6,
and C7 nerve roots generally form the long thoracic
nerve, and the C4 or C8 nerve roots rarely contribute
to the nerve.
A branch of the C5 nerve root innervated the upper
part of the serratus anterior muscle in all dissections.
The other nerve roots, apart from C5, supplied the up-
per part in 64 of 70 dissections, supporting the fact
that multiple nerve roots innervated the upper part.
Bernett
1
stated that the C5, C6, and C7 nerve roots
supplied the upper, middle, and lower parts, respec-
tively. On the other hand, Kato and Sato
13
found
that the C5 nerve root innervated the upper part, C6
innervated the whole of the serratus anterior, and
C7 innervated the lower part. Our results partially
agree with the findings of Bernett and Kato and
Sato. The upper part, which was innervated from mul-
tiple nerve roots, may rarely be affected by a single
nerve root injury. However, innervation of the middle
or lower part from a particular nerve root could easily
result in dysfunction after a single nerve root distur-
bance. Radiculopathy of the C7 nerve root, which sup-
plies the lower part, induces weakness of the serratus
anterior muscle and winging of the scapula.
18
The
current cases confirm this potential dysfunction.
There are 3 critical points for the long thoracic
nerve: penetration into the substance of the scalenus
medius muscle, a tight fascial band of tissue arising
from the inferior aspect of the brachial plexus, and an-
gulation over the second rib. Branches of the C5 nerve
root passed through the scalenus medius in 42 dissec-
tions, and 7 of the C6 nerve roots also pierced the sca-
lenus medius in our investigation. If paralysis of the
serratus anterior muscle results from compression of
the nerve at the scalenus medius muscle, one would
expect that the lower part of the serratus anterior mus-
cle (supplied by the C7 nerve root) would not be par-
alyzed and that there would be paralysis of the
rhomboid muscles, because the dorsal scapular nerve
supplying the rhomboids also passes through the sca-
lenus medius. The reason that we were not able to
demonstrate the tight fascial band of tissue proposed
by Hester et al
10
may be related to whether fresh or
embalmed cadavers were examined. Gregg et al
9
demonstrated only the bony structure, the second
rib, over which the long thoracic nerve was kinked.
However, the floor under the nerve is composed of
the upper part of the serratus anterior muscle as soft tis-
sue. If some soft tissue restricting excursion or transla-
tion of the long thoracic nerve near the second rib
existed, the nerve would be kinked or entrapped at
this point. Because we could not demonstrate such
a soft-tissue structure, there would be little opportunity
to disturb the nerve. We propose another possibility
for long thoracic nerve injury. Under a motion similar
to a tennis service, the nerve is repetitively or acutely
stretched between the fixed point at the substance of
the scalenus medius and the lower part of the serratus
anterior muscle. Finally, the limitation of this study is
that there has been no direct observation of entrap-
ment or a kinking point of the long thoracic nerve
similar to carpal tunnel or cubital tunnel syndrome, be-
cause the critical point for the long thoracic nerve can-
not be found as a result of the nerve trajectory under
the scapula.
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