Keywords
ultrasonography - children - sternum fracture - ultrasound
Introduction
Fractures of the sternum are rare, especially in children, with incidences ranging
from 0.5 to 3%.[1]
[2] These injuries occur predominantly due to strong deceleration forces and/or blunt
trauma to the chest in motor vehicle incidents. Forced flexion of the sternum across
the shoulder harness of the seatbelt can cause sternal fractures in children, while
fractures of the sternum without direct trauma are extremely rare.[3]
[4] Fractures of the sternum usually run transversely and are commonly located in the
middle part of the body or manubrium.[5]
To detect bone injury and pneumothorax, plain X-ray images of the thorax are frequently
obtained in patients who have experienced blunt chest trauma. Because of its subcutaneous
location, the sternum can be visualized easily by sonography. Since only few data
on the effectiveness of ultrasonic imaging in detecting sternal fractures in children
have been published, we report our experience with two patients to emphasize the usefulness
of sonography in the diagnosis of sternal fractures in children.
Case Report
A 13-year-old boy with acute anterior chest pain localized in the region of the sternum
was admitted to the emergency room. During a broad jump, he had experienced a cracking
noise in the area of his sternum. Physical examination revealed tenderness without
swelling above the body of the sternum. Auscultation of the lungs and heart revealed
no pathological findings, and the electrocardiogram (ECG) was normal. Anterior–posterior
chest X-ray was normal. Ultrasonic imaging revealed a transverse fracture of the manubrium
sterni with dorsal displacement of the distal fragment by 0.97 cm ([Fig. 1]) in the absence of pericardial effusion. The displaced sternal fracture without
combined intrathoracic injuries was confirmed by MRI ([Fig. 2]).
Fig. 1 Longitudinal ultrasonic image showing the transverse fracture of the manubrium sterni
with dorsal displacement of the distal fragment by 0.97 cm.
Fig. 2 T2-weighted sagittal MRI showing the fracture (indicated by arrow) of the sternum.
MRI, magnetic resonance imaging.
The second child, a 6-year-old girl, fell from her bicycle and hit her sternum with
the handlebar. She complained about persisting pain above the sternal body. Cardiopulmonary
examination was normal, and anterior–posterior chest X-ray showed no abnormality.
In the lateral chest view, no subtle fracture line or displacement was demonstrated
([Fig. 3]). Ultrasonic imaging identified a transverse fracture of the middle part of the
sternum without displacement or pericardial effusion ([Fig. 4]).
Fig. 3 Lateral chest X-ray without signs of fracture.
Fig. 4 Transverse ultrasonic image showing the transverse, nondisplaced fracture of the
corpus sterni (indicated by arrow).
Both sternum fractures were managed nonoperatively. Because of persisting chest pain,
especially during breathing, the children were admitted to the in-patient ward for
observation and pain management. Sport participation was discouraged for 3 months.
Sonographic follow-up after 9 months demonstrated consolidation of the fracture and
sufficient remodelling of the sternum in both children ([Fig. 5]).
Fig. 5 Longitudinal ultrasonic image obtained 9 months after injury showing consolidation
of the fracture and sufficient remodelling of the anterior outline of the sternum.
Ultrasonic imaging was performed by pediatric radiologists using a Philips iU22 scanner
(Philips AG Healthcare, Zürich, Switzerland) equipped with a 12–5 MHz linear transducer.
Transverse and longitudinal planes were described in supine position of the patient.
The longitudinal transducer position was found to be the best for visualization of
the transverse fractures.
Discussion
Causes of chest pain after blunt trauma in children may be pulmonary contusion, rib
fracture, pneumomediastinum, hemopneumothorax, cardiac, aortic, or diaphragmatic injury,
and sternal fracture.[6] Comprehensive medical history and clinical examination help to exclude associated
injuries. The presence of multiple rib fractures correlates better with intrathoracic
(pulmonary, cardiac, and aortic) or intra-abdominal injuries than severely displaced
sternal fractures.[7]
Diagnostic assessment of blunt chest injury usually includes plain chest X-ray and
in the case of suspected complex intrathoracic injuries, includes chest computed tomography
(CT).[8]
[9] Ultrasonic imaging in the diagnostic workup of pediatric fractures has not been
widely accepted. A retrospective study comprising 2,006 plain X-ray studies demonstrated
that fractures were detected in only 17.6% of injuries in children.[10] Moreover, sternal fractures may be missed when displacement is minimal, and only
conventional radiography is used.[11]
[12] In case of tiny sternal fractures, sonography has a higher diagnostic sensitivity
and specificity than conventional chest X-ray.[11] In our two cases, lateral chest X-ray missed the sternum fracture in one child.
Despite the well-documented diagnostic value of the CT scan, its use is limited due
to the effects of ionizing radiation on the growing tissue in children.[13]
[14] However, the CT scan remains an essential life-saving tool for diagnosing serious
thoracic injuries, as long as it is performed properly (pediatric CT protocol) and
justified clinically. In the child with the displaced sternum fracture, we performed
magnetic resonance imaging (MRI) of the thorax to rule out concomitant injuries of
the soft tissues surrounding the sternum. The MRI was performed without general anesthesia.
Sternal fractures are usually identified by standard lateral chest X-ray, which, however,
may be difficult to obtain in patients with multiple injuries.[2] In contrast, sonography is readily available at the patient's bedside and can easily
be performed in the prone position. Sonography is suitable for obtaining dynamic images
together with color Doppler studies and allows to examine subcutaneous structures
such as the sternum. Furthermore, it can accurately evaluate associated lesions, such
as hematomas and pleural or pericardial effusion. However, ultrasonography remains
an operator-dependent diagnostic tool and has a smaller scanning area when compared
with other imaging modalities, such as MRI, X-ray, or CT.[15]
Sonography has been used to detect stress fractures, to monitor the formation of callus
in fractures of long bones and enable early diagnosis of osteomyelitis as well as
in the screening for developmental dysplasia of the hip in infants.[16]
[17]
[18] In recent years, evidence has grown that sonography is more sensitive than conventional
X-ray in the assessment of sternal fracture, in particular when performed by an expert.[19] However, fissures less than 1 mm wide or nondisplaced epiphyseal fractures (Salter–Harris
type 1) are not detected reliably by sonography and therefore still rely on conventional
X-ray for diagnosis.[20] Furthermore, ultrasonic visualization of bone areas that reside deeply in soft tissue
may be insufficient because of the limited penetration depth.
Normal sternal development should also to be considered when evaluating the sternum
by sonography. The sternum, composed of the manubrium, mesosternum (the body, composed
of four parts) and xiphoid, develops from two lateral cartilaginous plates and a median
rudiment that begin fusing in the midline in cephalocaudal direction during fetal
development.[21]
[22] Each component of the sternum contains several ossification centers. Their pattern
of appearance and configuration may vary greatly with the age of the patient.[22]
[23] Since some ossification centers are discernible until adulthood, they may be misinterpreted
as a fracture in childhood. Failure of midline fusion may also be confused with a
fracture. To avoid confusion between normal development of the sternum and a pathological
finding, sound understanding of sternal development is indispensable, especially in
children.
Various congenital anomalies may affect the sternum and also mimic a fracture. These
include pectus excavatum (the sternum is displaced posteriorly and the ribs protrude
anteriorly) with or without a titled sternum (the sternum is oriented obliquely in
the horizontal axis), pectus carinatum (the sternum is displaced anteriorly), sternal
sclerotic band and cleft (vertically oriented midline bands; sternal clefts may occur
isolated or in association with an ectopia cordis and pentalogy of Cantrell), sternal
foramen, episternal ossicles (retro- or supramanubrial accessory bones), degenerative
osteoarthritis with or without osteophytes or cysts, osteomyelitis with lytic osseous
lesions, sternal dehiscence after sternotomy, and neoplasms.[24]
Isolated fractures of the sternum are uncommon, and their treatment is generally conservative
in the absence of concomitant injuries, and reduction is rarely required.[15] In our first case, the sternum was probably fractured by forced hyperflexion or
repeated trauma. Generally, the surrounding ligaments of the sternum and cartilaginous
attachments to the ribs are more elastic in children than in adults, making the sternum
of a child less susceptible to fractures.[25] Therefore, a standard protocol for diagnostic workup and treatment does not exist.
Given the remodelling capacity of the sternum in children, we decided to treat our
patients nonoperatively. Formation of callus and complete remodelling of the sternum
were monitored sonographically.
In conclusion, sternal fractures and their healing in children can easily be monitored
by ultrasonographic imaging using linear probes. Therefore, in case of an isolated
fracture of the sternum, we recommend the use of ultrasonic scanning as the first-line
diagnostic modality in children. If associated intrathoracic injuries are suspected
clinically, complementary diagnostic imaging modalities are indicated.
