Up to 8% of patients admitted with blunt chest trauma have sternal fractures,¹ caused primarily by anterior blunt chest trauma, usually from motor vehicle accidents when the chest strikes the steering wheel.² Mandatory seatbelt laws, now common in many parts of the world, are associated with an increased incidence of sternal fractures.³

Most sternal fractures are transverse, and a lateral radiographic view is diagnostic.² These fractures are often missed radiographically because lateral plain chest radiograph is not usually obtained during the initial trauma evaluation. Using a computed tomography (CT) scan, we diagnosed a vertical midline sternal fracture that was not visible on standard posteroanterior and lateral chest radiographs.

CASE REPORT

A 36 year old man who had been involved in a motor vehicle accident 2 days previously was transferred to our emergency department (ED) from a rural state hospital because of persistent chest pain. He had reported that his car had hit road barriers while he was driving at a speed of approximately 90 km/h and using a restraining seat belt. He was alert and oriented. Vital signs on presentation were in normal limits.

The patient complained of substernal chest pain that increased with inspiration, and of mild abdominal pain. On physical examination, there was a 4-cm, sutured incision on the right temporal scalp area. Pain and tenderness upon palpation of the anterior chest wall over the sternum and slight bruising from the seat belt across the sternal area were observed. Abdominal examination revealed tenderness on the right upper quadrant.

Electrocardiogram showed normal sinus rhythm. Laboratory results showed haematocrit at 43.9%, white blood cell count 8.9/mm³, and normal electrolytes. Creatinine kinase (CK) and CK myocardial band values were normal. Cardiac troponin-I level was 0.011 ng/ml (normal range 0.0–1 ng/ml). Chest radiograph in the supine position demonstrated widening of the upper mediastinium and increased cardiothoracic ratio. Lateral sternum radiograph showed no subtle fracture line or displacement (fig 1). Abdominal ultrasonography and echocardiographic studies were within normal limits. Although there was no abnormality of the sternum on all the previous radiological studies, we carried out a thoracic CT scan because of the patient’s intolerable chest pain. Continuous 3 mm axial sternal CT images showed a vertical mid-sternal, slightly displaced fracture. The fracture line was seen in the manubrium sterni extending to the body of the sternum. A manubriosternal synchondrosis line was seen on the right lateral side of the manubrium, and left costosternal joint widening was also detected (fig 2). No other significant thoracic injury was visible on the CT scan.

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Figure 1

 (A) Anteroposterior chest radiograph in the supine position shows widened upper mediastinium and increased cardiothoracic ratio. (B) Lateral sternum radiograph demonstrates no subtle fracture line or displacement.

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Figure 2

 (A) Thoracic CT axial images show a vertical midsternal, slightly displaced fracture (white arrow) on the manubrium sterni extending to the body of the sternum. Manubriosternal synchondrosis is seen on the right lateral side of the manubrium (arrowheads). Costosternal joints are also seen (black arrows). There is slight joint widening on the left costosternal joint compared with the right side. (B) Control CT scan shows sclerotic medullary bone changes caused by healing of the fracture line (arrowheads). Widening of the left costosternal joint had increased compared with the previous examination. (C) Coronal reformatted image shows the vertical midline fracture line more clearly.

The patient was admitted to the general surgery service for observation. He had no complications during the hospital course and was discharged the following day. Sclerotic medullary bone changes caused by healing of the fracture line were detected in the follow up CT scans 1 month later. Widening of the left costosternal joint compared with the previous examination was detected. A coronal reformatted image was also showed the vertical midline fracture line more clearly (fig 3). The patient had no discomfort during the follow up examinations.

DISCUSSION

The vast majority of sternal fractures involve the body of the sternum,⁴ with 8% being found at the manubriosternal junction.⁵ The interesting point of our case was the vertical course of the fracture line, which to our knowledge has not been previously reported.

Sternal fractures cannot be visualised on frontal chest radiographs and may be relatively inconspicuous on lateral chest radiographs.⁶ They are usually easily visible on axial or sagittal reconstructed CT scans.⁶ In one study, diagnosis of sternal fractures was achieved by anteroposterior chest radiograph in 32.1% and lateral radiography in 64.3% of patients.⁷ The authors diagnosed sternal fracture with CT in only one patient.⁷ In a more recent study, lateral sternal radiographs were found to be superior to CT in diagnosis of sternal fractures.⁸ However, in our case plain radiographs did not demonstrate the sternal fracture line; mediastinal widening was the only sign in the radiograph of the anteroposterior chest, while that of the lateral chest appeared normal.

Ultrasonography can be performed very quickly, is noninvasive, and may give sufficient information about sternal fractures.⁹ In our patient, we performed a CT examination after radiography because other chest wall areas needed to be examined for trauma.

CT scanning may reveal sternal fractures, yet is less sensitive than plain radiography, as the fracture lines may be positioned between image cuts.¹⁰ Suspicion of other chest injuries warrants CT scans.¹⁰ In a study, eight of nine sternal fractures were diagnosed by lateral radiographs, while only six of the fractures were seen on thoracic axial CT scans; the scans misdiagnosed three sternal injuries as normal.⁸ Sagittal or coronal reformatted CT images can show those fractures.⁸ In our case, a slightly displaced fracture line on the sternal midline was easily seen on axial CT images. The fracture was vertically oriented, starting from the manubrium sterni and proceeding through the body of the sternum. The separated bone ends demonstrated sclerosis as sign of healing on control CT images. Coronal reformatted images demonstrated the fracture line very clearly, and manubriosternal synchondrosis was also seen on the axial images. This synchondrosis is associated with asymmetry of the developing ossification centres, which range from normal via variants to unequivocal anomalies.¹¹

In some studies, occurrence of cardiac trauma has been shown in ∼20% of sternal fractures.^12–14 Furthermore, sternal fractures may be associated with myocardial contusion, which is often clinically silent.^15,16 Thus, diagnosis of sternal fractures is of clinical importance, and CT is the method of choice as a complementary or alternative imaging technique to plain radiographs in the emergency services.¹⁰

CONCLUSION

The use diagnostic imaging techniques for sternal fractures is a controversial subject in the literature. Plain radiographs seem to be the first choice of modality in the diagnosis of sternal fractures. We suggest thoracic CT with coronal reformatted images as a diagnostic technique when the suspicion of sternal fracture cannot be eliminated with conventional lateral chest radiographs.