CASE REPORT

Incomplete Avulsion Fractures of the Scapular Spine Caused byViolent Muscle Contraction
Takeshi Morioka, Takayuki Honma and Kiyohisa Ogawa

Orthopedic Surgery, Eiju General Hospital, Tokyo, Japan(Received for publication on July 5, 2013)(Revised for publication on September 9, 2013)(Accepted for publication on October 1, 2013)(Published online in advance on December 10, 2013)

Two percent of scapular fractures occur as a result of indirect trauma caused by traction of the muscles
and ligaments attached to the scapula. We present two cases involving adults with incomplete avulsion
fractures of the scapular spine caused by violent voluntary contraction of the deltoid muscle. Thesecases are the first reported avulsion fractures confined to the scapular spine medial to the spinoglenoid
notch. Although the fractures were incomplete, one patient had a typical symptom of scapular fracture− pseudo-rupture of the rotator cuff characterized by clinical signs of a complete rupture of the musculotendinous cuff. Although this symptom is generally thought to be caused by massive hemorrhaging
under the rotator-cuff muscle bellies, it may develop from modest bleeding through the formation of
an intramuscular hematoma and a resultant elevation in intramuscular pressure. Confirming the presence of tenderness on the scapular spine and performing appropriate imaging investigation constitute aclinically effective method for preventing misdiagnosis. (doi: 10.2302/kjm.2013-0004-CR; Keio J Med
63 (1) : 13–17, March 2014)

Keywords: scapular fracture, muscle violence, deltoid muscle, incomplete fracture, pseudo-ruptureof the rotator cuffIntroduction

Case 1

The incidence of fractures of the scapula is low, accounting for 0.5–1% of all fractures. Because such fractures primarily develop as a result of major direct trauma,
most cases (>80%) are complicated by serious injuries.
On the other hand, 2% of scapula fractures are caused
by indirect trauma, accounting for only 0.01% of all fractures.1 The cause of indirect trauma is the traction ofmuscles and ligaments attached to the scapula.
Presented herein are two cases featuring incomplete
avulsion fractures of the scapular spine caused by violent voluntary contraction of the deltoid muscle. Further
discussion of this extremely rare fracture is based on
information from the literature. The two patients gave
informed consent for their data to be presented in thisarticle.

A 25-year-old male graduate school student in good
health tripped while running during a softball game andelevated his right arm to almost 60° abduction and thrust
his hand vigorously onto the ground to prevent his fall.
He felt an intense pain in his right shoulder and visitedan orthopedic clinic where a diagnosis of scapular fracture was made. Subsequently, the spontaneous pain in hisupper scapular region worsened, and the patient visited
our clinic 2 days after the accident. Examination revealed
that active movement of the right shoulder was limited
in all directions. There was localized swelling with tenderness on the scapular spine 4 cm medial to the acromial angle, and the patient complained of pain in thatregion on downward pressing of the acromion. Radiography demonstrated an incomplete fracture of the scapu-

Reprint requests to: Kiyohisa Ogawa, MD, Orthopedic Surgery, Eiju General Hospital, 2-23-16 Higashi-Ueno, Taito-Ku, Tokyo 110-8645,Japan, E-mail: ogawa51@jcom.home.ne.jp
Copyright © 2013 by The Keio Journal of Medicine
13Morioka T, et al: Avulsion Fracture of the Scapular Spine

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Fig. 1 Radiographic findings in case 1.
(A) Anteroposterior view at the time of the first visit revealed a minimally displaced fracture of the scapular spine (arrow). (B) Eightweeks after injury, a 45° craniocaudal view showed the widened and unclearly delineated fracture line (arrowheads) resulting frombone absorption and osteogenesis.

lar spine (Fig. 1A). The arm was immobilized in a slingfor 1 week, after which the patient started passive rangeof motion exercises of the shoulder and was allowed toperform activities of daily living (ADL) within pain-freelimits. The patient returned to the clinic 8 weeks after
the accident and noted that pain during ADL had quickly
decreased during the first week and then had completelysubsided. There were no limitations in range of motion,
nor were there any drop arm signs. The patient reported no pain on resistive movement in various directions.
Shoulder radiograms showed concurrent resorption andosteogenic changes along the fracture line (Fig. 1B). The
patient was advised to avoid sporting activities for thefollowing month and was asymptomatic 10 years after
the accident.
Case 2
A 30-year-old male office worker in good health slipped
while washing his car. He abducted his arm to 45° andslammed the lateral aspect of his right elbow onto thedoor of the car to prevent his falling. At that time he heard
a cracking sound and felt a slight pain in his right shoulder. About 30 min later, however, he became completely
incapable of moving his upper limb because of severe
pain. He visited a local hospital where radiograms weretaken, and these were considered unremarkable. Thepain increased the following day and he visited the orthopedic clinic of another hospital where rotator cuff injury was suspected. Magnetic resonance imaging (MRI)
performed 5 days after the accident ruled out any suchinjury. Because intense pain had continued with any active motion of the shoulder, he was referred to our clinic

16 days after the accident. No obvious deformity, swelling, or redness was noted. Intense tenderness was evident in the center of the muscle belly of the supraspinatus
and infraspinatus. There was no limitation in the passive
range of shoulder motion, the drop arm sign was positive,
and intense pain was induced on resistive abduction evenwith the arm at the patient’s side. The radiograms taken at
the initial local hospital showed a fracture of the scapularspine (Fig. 2A). The MRI taken at the orthopedic clinicof another hospital revealed a tumor-like mass within
the supraspinatus muscle virtually coinciding with thefracture line (Fig. 2B). Because an adequate radiogram
showing the whole fracture line had not been obtained,
computed tomography (CT) was indicated and was carried out at our clinic 20 days after the accident (Fig. 2C).
The CT images confirmed that the fracture was confinedto the scapular spine, so the patient was allowed to use
the affected upper extremity and was started on passive
range-of-motion exercises 3 weeks after the accident. The
patient noted that although severe pain during ADL had
continued for one more week, it had gradually decreased.
Because pain did not interfere with his ADL 8 weeks after the accident, isotonic muscular strength exercises ofthe shoulder muscles were then initiated. An examination performed 4 months after the injury demonstrated
complete bone union on radiography (Fig. 2D), no limitation in the range of motion, and no pain during resistive
movement in any direction. The patient is asymptomatic
4 years after the accident.

Keio J Med 2014; 63 (1): 13–17

15Fig. 2 Imaging of case 2.
(A) Anteroposterior radiogram taken at a local hospital revealed a minimally displaced fracture of the scapular spine (arrow). (B) Findings of magnetic resonance imaging (MRI) taken at the orthopedic clinic of another hospital. Axial T2-weighted MRI demonstrated
a medium-intensity tumor-like mass with a surrounding linear high-intensity shadow (small arrow) and linear high-intensity shadows
consistent with the muscle fibers (arrowheads) within the supraspinatus as well as the fracture line (large arrow). (C) Three-dimensional CT images taken 20 days after injury revealed the whole fracture line starting at the scapular spine crest with slight displacement(arrow) and disappearing at the base of the scapular spine (arrowhead). (D) Four months after injury, a 45° craniocaudal radiogramindicated bone union without any displacement (arrow).

Discussion
Many muscles are attached to the scapula, and fractures
can develop as a result of contraction of these muscles.
Such fractures are grossly classified as avulsion fractures (caused by a single violent muscle contraction) or
stress or fatigue fractures (caused by repetitive sports- orwork-related movement). Avulsion fractures are generally classified into those caused by involuntary muscle
contraction and those caused by voluntary muscle contraction. Fractures of the scapula resulting from involuntary muscle contraction have been reportedly caused
by uncoordinated muscle contraction associated withelectroconvulsive therapy, accidental electric shock,2,3
epileptic seizures,2 and severe tetanus.4 In contrast, avulsion fractures caused by voluntary muscle contraction
arise from resisted muscle pull as a result of trauma or
unusual exertion.2 Reported scapular fracture sites andthe possible causative muscles are diverse.2,5–8 The coracoid, acromion, and scapular spine, which are generally
referred to as scapular processes, are particularly prone
to avulsion fractures because of their anatomical andstructural characteristics. Fractures of the coracoid possibly occur as a result of traction of the conjoint tendon
along with or without the pectoralis minor.9,10 Fracturesof the anatomical acromion anterior to the acromial angle

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were reported in two adolescents.2,11 Kuhn et al. reported
avulsed-type fractures occurring in the distal or posterolateral acromial region in three patients.12 Fractures of thescapular spine medial to the acromial angle that extended
to the spinoglenoid notch also occurred in two men.1,13
The cause of these seven fractures occurring in the acromion and scapular spine was considered to be tractionof the deltoid muscle. The fracture lines in our two cases
were obvious and were slightly dilated in the crest of thescapular spine and disappeared at the junction between
the scapular spine and scapular body. This fact indicatesthat the force generating these fractures was a downward
force acting on the lateral part of the scapular spine oracromion. Therefore, the violent traction of the deltoid
muscle presumably caused the fractures in our two cases
because neither patient reported receiving a direct blow
to their shoulder at the time of injury. The present cases
are the first reported avulsion fractures confined to thescapular spine medial to the spinoglenoid notch caused
by a resisted deltoid muscle pull as a result of trauma orunusual exertions.
The previously reported sites of stress or fatigue fractures of the scapula and the muscles possibly producing
such fractures vary. Stress fractures of the acromion or
the scapular spine were previously uncommon and were
found to be related to cuff-tear arthropathy, work-related
activities, or sporting activities such as baseball, golf, orfootball.14–18 Recently, the occurrence of such fractures
has increased considerably as a result of complicationsof reverse total shoulder arthroplasty.19,20 Because of theworldwide application of this procedure, even stress fractures confined to the scapular spine medial to the spinoglenoid notch are becoming common.
We often encounter fractures of the scapula that on radiograms are suggested to be incomplete fractures. It isreasonable to believe that an incomplete fracture of thescapula can occur in adults because incomplete fracturesof the ribs, which have the same thin cortex as the scapula, have commonly been observed.21 However, insufficient attention has been paid to these fractures in theliterature. Although a transverse greenstick fracture of
the center of the scapular body caused by direct trauma
in a 12-year-old boy has been reported, and Armitage etal. mentioned the existence of incomplete fractures of thescapular bodies,22,23 our two cases are the first to featureisolated incomplete fractures confined to the scapularspine. Even though their fractures were incomplete, oneof our two patients presented with a typical symptom ofscapular fracture, i.e., pseudo-rupture of the rotator cuff.
This pseudo-rupture is characterized by the clinical signsof a complete rupture of the musculotendinous cuff including a positive drop arm test and inability to abduct thearm.24 This symptom is thought to be caused by massive
hemorrhaging under the bellies of the cuff muscles.24 In
our second case, intense pain during ADL and the inability to abduct the arm lasted 4 weeks. Because the frac-Morioka T, et al: Avulsion Fracture of the Scapular Spine

ture was incomplete and localized in the scapular spine,severe pain during ADL should generally have subsided
within 1 week in line with diminishing acute traumaticsymptoms, as was seen in our first case. When the causesof prolonged severe pain and inability to abduct the armin this case are analyzed, intramuscular hematoma is
considered to be the most probable cause, rather than theincomplete fracture itself. Therefore, massive bleeding is
not essential to produce this symptom of pseudo-ruptureof the rotator cuff because it may develop from modest
bleeding through the formation of an intramuscular hematoma and a resultant increase in intramuscular pressure. A diagnosis of these fractures is established basedon imaging, and CT is preferable to radiography becauseradiography is much less sensitive in delineating fracturesof the glenoid, coracoid process, and scapular spine.25 As
in our first case, however, sharply defined images may beobtained in an appropriate radiographic view in patientswith an obvious injury location.
In conclusion, we presented two cases in which the patients had incomplete avulsion fractures of the scapularspine caused by violent voluntary contraction of the deltoid muscle. Confirming the presence of tenderness on
the scapular spine and performing appropriate imaging
investigations constitute an effective method for preventing misdiagnosis.
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