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Carvalho SC et al. / Snapping scapula syndrome
262 Radiol Bras. 2019 Jul/Ago;52(4):262–267
Pictorial Essay
Snapping scapula syndrome: pictorial essay
Síndrome da escápula em ressalto: ensaio iconográco
Stefane Cajango de Carvalho1,a, Adham do Amaral e Castro1,b, João Carlos Rodrigues1,c, Wagner Santana
Cerqueira2,d, Durval do Carmo Barros Santos1,e, Laercio Alberto Rosemberg1,f
1. Hospital Israelita Albert Einstein, São Paulo, SP, Brazil. 2. A.C.Camargo Cancer Center, São Paulo, SP, Brazil.
Correspondence: Dr. Adham do Amaral e Castro. Hospital Israelita Albert Einstein – Departamento de Radiologia e Diagnóstico por Imagem.
Avenida Albert Einstein, 627, Jardim Leonor. São Paulo, SP, Brazil, 05652-901. Email: adham.castro@gmail.com.
a. https://orcid.org/0000-0002-6672-6045; b. https://orcid.org/0000-0003-0649-3662; c. https://orcid.org/0000-0002-7107-2621;
d. https://orcid.org/0000-0003-0203-6376; e. https://orcid.org/0000-0002-5210-3605; f. https://orcid.org/0000-0003-4395-1159.
Received 3 December 2017. Accepted after revision 23 February 2018.
How to cite this article:
Carvalho SC, Castro AA, Rodrigues JC, Cerqueira WS, Santos DCB, Rosemberg LA. Snapping scapula syndrome: pictorial essay. Radiol Bras. 2019
Jul/Ago;52(4):262–267.
Abstract
Resumo
Snapping scapula syndrome manifests as an audible or palpable crackling during the sliding movements of the scapula over the
rib cage, often perceived during physical or professional activities. It can be caused by morphological alteration of the scapula and
rib cage, by an imbalance in periscapular musculature forces (dyskinesia), or by neoplasia (bone tumors or soft tissue tumors).
In this pictorial essay, we review the main causes of snapping scapula syndrome, exemplied by a collection of didactic cases.
Keywords: Scapula; Joint diseases/diagnostic imaging; Shoulder.
A síndrome da escápula em ressalto manifesta-se como uma crepitação audível ou palpável durante os movimentos de desli-
zamento da escápula sobre o gradil costal. Frequentemente percebida em atividades físicas ou prossionais, as suas causas
podem ter origem na alteração morfológica da escápula e gradil costal, no desequilíbrio de forças da musculatura periescapular
(discinesia) ou ainda em tumores ósseos ou de par tes moles. O presente estudo revisou de forma ilustrativa as principais causas
da síndrome da escápula em ressalto, exemplicadas por meio de uma coletânea de casos didáticos.
Unitermos: Escápula; Doenças articulares/diagnóstico por imagem; Ombro.
consists of the serratus anterior and subscapularis muscles,
containing the infraserratus bursa, located between the
serratus anterior muscle and the rib cage, and the supra-
serratus bursa, located between the serratus anterior and
subscapularis muscles(3). Figure 1 illustrates the bursae
and their respective anatomical relationships. The control
and proper positioning of the scapula are fundamental for
the correct functioning of the glenohumeral joint. During
normal shoulder movement, the scapula needs to be prop-
erly aligned in multiple planes of motion, a situation that
depends on harmonic and synchronous actions between
the various scapular muscles. The scapula receives differ-
ent combinations of forces exerted by the muscles inserted
therein, producing movements of abduction, adduction, el-
evation, depression, and rotation (Figures 2 and 3). There
is an arc-of-motion pattern between the glenohumeral
joint and the scapulothoracic joint, known as the scapu-
lohumeral rhythm, which has a 2:1 ratio. In other words,
for every two degrees of movement of the humerus, the
scapula moves one degree(6), as depicted in Figure 4.
ANATOMICAL VARIATIONS AND DISEASES
THAT CAN CAUSE THE SYNDROME
Superomedial angle of the scapula and anatomical
variations
The scapulothoracic joint is cushioned by the serra-
tus anterior and subscapularis muscles, as well as by the
bursae(7). The superomedial angle, inferomedial angle, and
DEFINITION AND EPIDEMIOLOGICAL ASPECTS
Snapping scapula syndrome is dened as an audible or
palpable clicking of the scapula during movements of the
scapulothoracic joint(1). It typically affects young, active
patients, who often report a history of pain, resulting from
overuse, during rapid shoulder movements or during sports
activities(2). These symptoms can have insidious onset, can
occur after a change in the pattern of physical activity, or
can be associated with trauma(3).
ANATOMY AND BIOMECHANICS
The scapula is a at, triangular bone that lies between
the second and seventh ribs. As previously described(3–5), it
has two surfaces (ventral and dorsal), three borders (supe-
rior, lateral, and medial), and three angles (superomedial,
inferomedial, and lateral).
The articulation between the scapula and the rib cage
is one of the most incongruous in the human body, be-
cause it does not have true joint structures but rather is
surrounded by a complex of muscles, which is divided into
three layers: supercial, intermediate, and deep. The su-
percial layer comprises the trapezius and latissimus dorsi
muscles, which can be accompanied by a bursa located be-
tween the inferomedial angle and supercial bers of the
latissimus dorsi muscle(3). The intermediate layer consists
of the major rhomboid, minor rhomboid, and levator scapu-
lae muscles. The trapezoid bursa lies between the trapezius
muscle and the base of the shoulder blade. The deep layer
0100-3984 © Colégio Brasileiro de Radiologia e Diagnóstico por Imagem
http://dx.doi.org/10.1590/0100-3984.2017.0226
Carvalho SC et al. / Snapping scapula syndrome
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Radiol Bras. 2019 Jul/Ago;52(4):262–267
medial border of the scapula are relatively less protected by
underlying muscles and bursae, and the upper medial bor-
der and lower pole exhibit wide anatomical variability(4,7).
When no obvious deformity is found, one should look for
anatomical variations, such as an anomalous anterior cur-
vature of the superomedial angle of the scapula, which is
considered one of the main causes of the syndrome. The
superomedial angle of the scapula has been measured in
anatomical specimens and found to range from 124° to
162° (mean, 144.34 ± 9.09°)(7); when the angle is lower
than 142°, the chances of scapular snapping increase(8).
The superomedial angle is measured on the anterior sur-
face of the scapula, with three anatomical reference points
(Figures 5 and 6): the superior angle, the spine, and the
inferior angle. A bone projection at the lower pole is the
second most common site for symptoms(4) (Figure 7).
The Luschka tubercle
The Luschka tubercle is a hook-shaped bony protuber-
ance, located at the upper medial border of the scapula,
which can reduce the space between the scapula and the rib
cage and be a predisposing factor for scapular snapping(7).
Scapular dyskinesia, insufciency of the serratus
anterior muscle, and injury of the long thoracic nerve
Scapular dyskinesia, a common clinical nding, is
dened as abnormal movement, positioning, or function
of the scapula during shoulder movement. It can be the
cause or consequence of many forms of shoulder pain
and dysfunction. There are multiple causes of dyskinesia.
Articulatory causes include acromioclavicular joint ar-
throsis, glenohumeral joint instability, and glenohumeral
joint disorder. Musculoskeletal causes include thoracic
Figure 3. Schematic representation of the movement of the scapula, showing, from left to right, abduction/adduction, rotation, and upward/downward movements.
Figure 1. Schematic representation of the musculature and bursae involved in
snapping scapula syndrome.
Pectoralis major
Subscapularis
Trapezius
Trapezoid
bursa
Serratus
anterior
Supraserratus
bursa
Infraserratus
bursa
Figure 2. Schematic representation of the biomechanical vector of the mus-
culature involved in scapular movement. The upper and lower portions of the
trapezoid are shown in pink, and the central portion is translucent, demarcated
by the dotted line.
Rhomboids
Trapezius
Levator scapulae
Rhomboids
Trapezius
Levator scapulae
Serratus anterior
Pectoralis minor
*Trapezius
Serratus anterior
Trapezius
Pectoralis minor
#Rhomboids
Pectoralis minor
Levator scapulae
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Figure 4. Schematic representation of the 2:1 scapulohumeral rhythm. For ex-
ample, during a 180° abduction of the arm, 60° are achieved by rotation of
the scapula and 120° are achieved by rotation of the humerus.
Figure 5. Schematic representation of the costal surface of the right scapula,
showing the ABC measurement of the superomedial angle.
Figure 6. A 42-year-old male patient with a 7-year history of intermittent left-sided scapular pain, accompanied by snapping. The patient had been swimming,
walking, and cycling on a regular basis. Sagittal MRI of the left scapula, with fat-saturated T1- and T2-weighted sequences (A and B, respectively), showing a 122°
reduction in the superomedial angle of the scapula (the black lines in A indicate how the angle is measured), with a consequent reduction in the space between
the second rib and the superior border of the scapula. Mild muscular edema and slight edema of the adjacent (second) rib (arrow in B).
A B
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kyphosis and nonunion of a clavicular fracture, as well as
shortening, rotation, or angulation of the clavicle. Neuro-
logical causes include paralysis of the long thoracic nerve,
paralysis of the eleventh cranial nerve, and cervical ra-
diculopathy(9), as depicted in Figures 8 and 9. The most
common mechanisms involve imbalances of the intrin-
sic musculature, with inexibility or inhibition of normal
muscle activation(9). Scapular snapping can be present
in dyskinesias, because the abnormal movements bring
the extremities of the scapula into closer proximity to the
rib cage. Regardless of the cause of dyskinesia, the nal
result in most cases is a scapula in pronation, which is
not conducive to optimal shoulder function and results in
subacromial space reduction with symptoms of impinge-
ment(9).
Sequelae of fractures of the scapula and rib cage
The sequelae of fractures of the scapula and rib cage
can cause bone deformities. Such deformities can increase
the friction among the structures of the scapulothoracic
joint(10).
Figure 8. A 9-year-old female patient with a 1-month history of elevation of the right scapula, unrelated to pain, trauma, or surgery. A: Three-dimensional CT
reconstruction of the rib cage showing winging of the right scapula (arrow). B: Axial CT scan, with a soft-tissue window setting, showing denervation with atrophy
and fatty replacement of the serratus anterior muscle (arrow), showing the contralateral side for comparison. There was no evidence of extrinsic compression of
the long thoracic nerve.
A B
Figure 7. An 87-year-old male patient complaining of bulging of the posterolateral thoracic wall. The patient had been swimming on a regular basis. Contrast-enhanced
axial MRI of the left scapula, with fat-saturated T1- and T2-weighted sequences (A and B, respectively), showing uid distention and parietal enhancement of the
infraserratus bursa (arrows) with a uid–uid level (arrow in A), due to a bone projection in the inferomedial angle of the scapula, as shown on a CT scan (arrow in C).
A B C
Figure 9. A 32-year-old female patient with a 3-month history of shoulder pain
and scapular asymmetry. The patient had been running on a regular basis.
Axial T2-weighted fat-saturated MRI scan of the scapulae showing denervation
and edema of the serratus anterior muscle (arrow), without signicant atrophy.
There was no evidence of extrinsic compression of the long thoracic nerve.
Bursitis
Scapulothoracic bursitis can occur after a single trau-
matic insult, as a result of repetitive movements of the
Carvalho SC et al. / Snapping scapula syndrome
266 Radiol Bras. 2019 Jul/Ago;52(4):262–267
scapulothoracic joint, or as a result of scapular dyskinesia.
Abnormal scapular movement can be caused by overuse of
the muscles, muscle imbalance, or pathological conditions
of the glenohumeral joint(3). When the muscles of the cos-
tal surface of the scapula decrease in size, the scapula ro-
tates forward, coming into closer proximity to the rib cage,
generating friction with the chest wall during movement,
causing inammation in the scapulothoracic space(3), as
shown in Figures 7 and 10.
Bone tumors
Osteochondroma, also known as exostosis, is the
most common benign primary bone tumor of the scapula,
being solitary in approximately 90% of cases and multiple,
in the form of hereditary multiple exostoses, in approxi-
mately 10%. Such tumors are considered alterations of
the growth plate, specically its failure to increase in size
during skeletal maturation(11). They usually involve the
metaphysis of long bones and, more rarely, the scapula (in
4–6% of cases). An osteochondroma can be symptomatic,
mainly due to its mass effect, creating the appearance of
scapular winging, together with crackles, and altering the
scapulothoracic movement. It can also cause neurovascu-
lar compression, fractures, inammation of the bursa, or
malignant transformation(11) (Figures 10–12). Although
scapular chondrosarcoma is rare, the scapula is the sec-
ond most common site of involvement of this disease, es-
pecially among men between 40 and 70 years of age(3,4).
Elastobromas
An elastobroma is a benign soft tissue tumor with
slow growth and a prevalence rate of up to 24% in the
elderly, being most common among women between 55
and 70 years of age. Elastobromas are believed to occur
Figure 10. A 46-year-old female patient, in follow-up for osteochondroma for 8 years and presenting with a 7-month history of constant pain. CT of the scapula, in
coronal and axial slices (A and B, respectively), demonstrates pedunculated osteochondroma in the anterior superior aspect of the scapula, in close proximity to
the posterior border of the rst and second ribs on the left (arrow in A). Marked uid distention in the region of the supraserratus bursa (arrow in B).
BA
Figure 11. A 14-year-old male patient with a 6-month
history of bulging and discomfort in the left scapula.
The patient had been playing water polo on a regular
basis. MRI of the left scapula, with a sagittal slice
and a fat-saturated T2-weighted sequence, show-
ing osteochondroma in the superomedial angle of
the scapula, with a thin cartilaginous layer, invading
the space between the rst and second ribs (arrow).
Edema of the musculature between the osteochon-
droma and the rib cage, suggesting friction.
Figure 12. An 18-year-old male patient with pain
in his right arm. X-ray showing broad-based exos-
tosis in the lower third of the scapular body (sub-
scapular fossa, arrow).
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Radiol Bras. 2019 Jul/Ago;52(4):262–267
in response to repetitive microtrauma caused by friction
between the scapula and the chest wall. An elastobroma
is typically located at the lower pole of the scapula, deep
within the serratus anterior and latissimus dorsi muscles.
It can manifest as an increase in subscapular or infra-
scapular volume, moderate discomfort or pain, crackles,
clicking (snapping), or a blocked scapula(12), as depicted
in Figures 13 and 14.
CONCLUSION
Although snapping scapula syndrome is rare, it can
cause severe pain and functional limitation. Therefore, ra-
diologists should be able to recognize its imaging ndings.
In this pictorial essay, we have illustrated the main causes
of the syndrome, using imaging examinations.
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Figure 13. A 69-year-old male patient with a 90-day history of bulging, snap-
ping, and pain in the left scapular region. The patient had engaged in weightlift-
ing on a regular basis. Axial T1-weighted MRI of the left scapula, showing an
elastobroma deep within the serratus anterior muscle, interposed between
the rib cage and the inferior angle of the scapula (arrow).
Figure 14. A 55-year-old male patient with increased volume in the left scapu-
lar region. Ultrasound (A) showing a predominantly hypoechoic, heterogeneous
formation (arrow), located between the scapula and the rib cage. On CT (B), the
formation presents soft-tissue density and brofatty striae, with a well-dened
location between the costal grating and the ventral portion of the anterior ser-
ratus muscle, at the subscapular and infrascapular level, consistent with dor-
sal elastobroma.
A
B