Surgical Science, 2013, 4, 1-5
http://dx.doi.org/10.4236/ss.2013.49A001 Published Online September 2013 (http://www.scirp.org/journal/ss)
Elasticity of the Coracoacromial Ligament in Shoulders
with Rotator Cuff Tears: Measurement with Ultrasound
Elastography
Hiroaki Kijima1*, Hiroshi Minagawa2, Tatsuru Tomioka3, Shin Yamada1, Koji Nozaka1,
Hidetomo Saito1, Yoichi Shimada1
1Department of Orthopedic Surgery, Graduate School of Medicine, Akita University, Akita, Japan
2Department of Orthopedic Surgery, Johto Orthopedic Clinic, Akita, Japan
3Department of Orthopedic Surgery, Yokote Municipal Hospital, Yokote, Japan
Received June 16, 2013; revised July 18, 2013; accepted July 26, 2013
Copyright © 2013 Hiroaki Kijima et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Background: The symptoms of rotator cuff tear vary and may even be absent. Thus, the symptoms cannot be explained
solely by the presence of rotator cuff tear, and other factors are thought to be involved. Because the rotator cuff comes
in contact with the coracoacromial ligament, the elasticity of the ligament may be a factor of the symptoms. The pur-
pose of this study was to clarify the elasticity of the coracoacromial ligament in live shoulders with rotator cuff tears.
Methods: Forty-one shoulders in 24 persons were enrolled in this study. The average age was 52 years old (range, 15 -
84 years old). We investigated the presence of rotator cuff tear and measured the elasticity of the coracoacromial liga-
ment by ultrasound elastography (EUB-7500, HITACHI, Japan). Ultrasound elastography was a useful method to quan-
tify the strain of soft tissue when pressure was added. The strain ratio (the ratio of strain of the coracoacromial ligament
to that of the rotator cuff) was used as the index of the elasticity of coracoacromial ligament. Thus, the higher the strain
ratio was, the softer the ligament was. Results: The strain ratio of the coracoacromial ligaments without rotator cuff tear
showed a negative correlation to the age (r = −0.825, P < 0.01). The strain ratio of the ligaments with rotator cuff tear
(23.75 ± 15.05, 69.6 years old) was higher than that of the older ligaments without cuff tear (12.62 ± 7.94, 64.6 years
old) (P = 0.0486). In shoulders with rotator cuff tear, the strain ratio of the ligaments with pain (14.37 ± 10.15, 66.7
years old) was lower than that of ligaments without pain (33.12 ± 13.59, 69.1 years old) (P = 0.0221). Conclusions:
The coracoacromial ligament became stiffened with aging but softened with the existence of rotator cuff tear. The liga-
ments with symptomatic cuff tear are more stiffened than the ligaments with asymptomatic cuff tear.
Keywords: Rotator Cuff Tear; Coracoacromial Ligament; Pain; Ultrasound Elastography
1. Introduction
Epidemiological studies have shown that low back pain,
knee pain, and shoulder pain are common. The preva-
lence of low back pain and knee pain increases with ag-
ing, whereas shoulder pain tends to decrease at the peak
in 50 - 60 generations [1-3].
Rotator cuff tear is a common cause of shoulder pain.
The prevalence of rotator cuff tear also increases with
aging [4]. However, symptoms of rotator cuff tear vary
and may even be absent. Thus, the symptoms cannot be
explained solely by the presence of rotator cuff tear, and
other factors are thought to be involved. If these factors
are clarified, various approaches to pain reduction are
possible.
Previous study of coracoacromial ligament elasticity
with scanning acoustic microscopy, which can be used to
evaluate the elasticity of tissue at the microscopic level,
have shown that coracoacromial ligaments that show
advanced degeneration have a higher elastic modulus [5].
This result suggests that because the coracoacromial liga-
ment degenerates histologically and stiffens with aging,
the contact pressure of the rotator cuff and the coracoac-
romial ligament increases and the prevalence of shoulder
pain or rotator cuff tear increases with aging. Same pre-
vious study has also shown that the ligaments in shoul-
ders with rotator cuff tears have a lower elastic modulus
*Corresponding author.
C
opyright © 2013 SciRes. SS

H. KIJIMA ET AL. 2
[5]. From this result, we can hypothesize that the cora-
coacromial ligament softens after the onset of rotator cuff
tear, and that the prevalence of shoulder pain decreases
in turn because the contact pressure of the ligaments and
the rotator cuff decreases. To confirm these possibilities,
it is necessary to examine the relationship between shoul-
der pain and the elasticity of the coracoacromial ligament
in vivo. Many researchers have used ultrasound elasto-
graphy to evaluate the elasticity of lesions of the breast,
prostate, or liver in vivo [6-10]. The purpose of the pre-
sent study was to clarify elastic changes with aging of the
coracoacromial ligament and to clarify the relationship
between the elasticity of the coracoacromial ligament and
symptoms of rotator cuff tears by means of ultrasound
elastography.
2. Materials and Methods
Forty-one shoulders (29 in male subjects and 12 in fe-
male subjects) in 24 healthy volunteers and patients, who
had come to our hospital, were examined in this study.
The average age of the subjects was 52 years (range, 15 -
84 years). Consent for this study was obtained from our
institution, and informed consent was obtained from all
subjects.
We first asked subjects whether they had shoulder pain
and examined them whether their rotator cuff tore with
an ultrasound scanner (EUB-7500, Hitachi, Tokyo, Ja-
pan). Next, the elasticity of coracoacromial ligament was
assessed.
The shoulders were classified into 2 groups: an RCT
group (12 shoulders) with rotator cuff tears, and a normal
group (29 shoulders) without rotator cuff tears. Of the
shoulders in the RCT group, those with pain were placed
in the symptomatic group (6 shoulders), and those with-
out pain were placed in the asymptomatic group (6 shoul-
ders). Of the shoulders in the normal group, those of
persons younger than 50 years old were placed in the
younger group (19 shoulders), and those of persons older
than 50 years old were placed in the older group (10
shoulders). All shoulders without rotator cuff tears had
no symptoms. No significant difference was observed
between the age of the older group and that of the RCT
group or between the age of the symptomatic group and
that of the asymptomatic group.
We classified into RCT group when the rotator cuff
surface was concave or when the rotator cuff was not
detected in longitudinal image of cuff tendon with ultra-
sonography. The predictive positive value of this method
was reported previously to be 100% [11]. We did not
measure the size of rotator cuff tear.
An ultrasound scanner (EUB-7500, Hitachi, Tokyo,
Japan) was used to evaluate the elasticity of the cora-
coacromial ligament. Ultrasound elastography is a me-
thod of assessing tissue elasticity on the basis of the rela-
tive strain caused when pressure is applied from the skin
with the ultrasound probe. The strain ratio, which is the
ratio of the strain of the coracoacromial ligament to the
strain of the rotator cuff, was used as an index of cora-
coacromial ligament elasticity in this study. Therefore,
the higher the strain ratio is, the softer the coracoac-
romial ligament is, because the coracoacromial ligament
strains more easily than does the rotator cuff when the
same amount of pressure is applied.
The longitudinal image of the coracoacromial ligament
was depicted with the coracoid process and acromion as
landmarks (Figure 1) and next, by turning the probe 90
degrees, the axial image of the ligament was depicted.
When the position of the coracoacromial ligament on the
axial image was inarticulate, this was confirmed by re-
ferring to the position of the thoracoacromial artery with
Doppler imaging. The B-mode axial image and the elas-
tographic image of the coracoacromial ligament was dis-
played on the right and left screens, respectively, of a
2-screen display (Figure 2). Then, we determined the
strain ratio B/A, which was the ratio of the strain of the
coracoacromial ligament (B) to the strain of the rotator
cuff (A) (Figure 2). Pearson’s correlation coefficients
were calculated between ages and strain ratios, and Stu-
dent’s t-test was used to compare strain ratios within each
group. Significance was set at the P < 0.05 level.
3. Results
The strain ratio of the normal group was negatively cor-
related with the subject’s age (r = −0.825, P < 0.01; Fig-
ure 3). The strain ratio of the RCT group was higher than
that of the older group without a significant difference in
the age of the RCT group (Figure 4). In the RCT group,
the strain ratio of the symptomatic group was lower than
that of the asymptomatic group (Figure 5).
4. Discussion
The coracoacromial ligament stiffened with aging. There-
fore, this stiffened ligament may be a causative factor for
rotator cuff tears because the ligament comes in contact
with the rotator cuff. On the other hand, the coracoac-
romial ligament softened when a rotator cuff tear was
present. This softening of the ligament might be related
to spontaneous pain relief often observed in the natural
history of rotator cuff tears, because ligaments in cases of
asymptomatic cuff tear are softer than ligaments in cases
of symptomatic cuff tear.
Ultrasound elastography, which was developed in
1991, can noninvasively quantify the strain of objects
[12]. Ultrasound elastography detects displacements of
organization when static pressure is applied. In other

H. KIJIMA ET AL. 3
Figure 1. Ultrasonographic image of the coracoacromial ligament (B-mode longitudinal image). Ac: Acromion; CP: coracoid
process; arrow: coracoacromial ligament.
Figure 2. Ultrasound elastographic image. The right image is a B-mode axial image of the coracoacromial ligament, and the
left image is an elastographic image of this ligament. RC: rotator cuff; Delt: deltoid muscle; and arrow: coracoacromial liga-
ment.

H. KIJIMA ET AL. 4
Figure 3. The relationship between the strain ratio and age
in the normal group. The strain ratio of the normal group
was negatively correlated with age (r = −0.825, P < 0.01).
Figure 4. The difference in the strain ratio between shoul-
ders with and without rotator cuff tears. The strain ratio of
the RCT group was higher than that of the older group
without a significant difference in the age of the RCT
group.
Figure 5. The difference in the strain ratio in shoulders with
rotator cuff tears between those with and without pain. In
the RCT group, the strain ratio of the symptomatic group
was lower than that of the asymptomatic group.
words, the degree of tissue extension under external pres-
sure is recorded with a high-resolution ultrasound scan-
ner, and the elasticity of the tissue is evaluated through
this correlation. Because ultrasound elastography can de-
tect histological changes related to tissue elasticity in real
time [13,14], its effectiveness in the diagnosis of lesions
of the prostate [6,7], breast [8,9], and liver [10] has been
reported. To our knowledge, the present study is the first
to use ultrasound elastography in orthopedics. This me-
thod is a useful technique that can be applied to many
objects, such as muscles, tendons, and peripheral nerves,
because it can distinguish organizations and quantify ela-
sticity differently from the muscle rigidity meter, which
is conventionally used to measure body hardness.
The strain ratio of the coracoacromial ligament was
negatively correlated with age. This result indicates that
the coracoacromial ligament stiffens with aging. Stiffen-
ing of the coracoacromial ligament causes an increase in
the contact pressure between the coracoacromial liga-
ment and the rotator cuff, and this increase in pressure
may cause degeneration of the rotator cuff. In addition,
stiffening of this ligament may lead to subacromial spur
formation, because the subacromial spur has been recog-
nized as a traction osteophyte of the coracoacromial liga-
ment. Therefore, the stiffening of the coracoacromial li-
gament may be an etiological factor in rotator cuff tears
and may support the finding that the prevalence of rotator
cuff tears increases with aging.
The coracoacromial ligament is suggested to soften
after a rotator cuff tore, because ligaments of shoulders
with rotator cuff tears are softer than ligaments of age-
matched shoulders with a normal cuff. Previous histo-
logical study also suggested that the coracoacromial liga-
ment was softened when its fiber structure collapsed as
degeneration progressed with the rotator cuff tear [5].
And the present study supports that previous report, in
vivo. In addition, the coracoacromial ligaments of shoul-
ders with asymptomatic rotator cuff tears are particularly
soft. Therefore, the softening of the coracoacromial liga-
ment may be related to the development of asymptomatic
rotator cuff tears. The subacromial bursa between the
coracoacromial arch and the rotator cuff contains many
free nerve endings. Softening of the coracoacromial liga-
ment may decrease the contact pressure between the
coracoacromial ligament and the rotator cuff. For rotator
cuff tears, repair of the cuff is one treatment method.
However, we can expect an effective treatment to de-
crease pressure under the coracoacromial ligament.
One limitation of the present study is that we have not
considered other factors for example subacromial bursa,
biceps tendon, or acromioclavicular joint. Another limi-
tation of the present study is that the strain quantified
with ultrasound elastography is a relative value. In this
study, the strain ratio was useful for an index of the con-
tact pressure between coracoacromial ligament and rota-
tor cuff, because the strain ratio is not the hardness itself
of coracoacromial ligament but the ratio of the easiness
of strain of coracoacromial ligament to the easiness of
strain of rotator cuff. And, the factor that we paid atten-

H. KIJIMA ET AL. 5
tion to as one of the causes of the shoulder pain was a
rise of the contact pressure between coracoacromial liga-
ment and rotator cuff.
To apply the results of this study clinically, a technical
development that will allow the elasticity to be evaluated
as an absolute value in vivo is needed. If this technology
is achieved, we conduct a same investigation in more
numerous numbers, easily. When we can measure the
elasticity of coracoacromial ligaments in vivo, the risk of
rotator cuff tear or the possibility of pain relief can be
predicted.
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