Morbidity and mortality associated with fracture of the sternum due to blunt trauma, by fracture type and location

Objective To examine the relationship that the types and locations of fractures of the sternum have with mortality and morbidity. Materials and Methods We analyzed the records of 115 patients diagnosed with fracture of the sternum, due to blunt trauma, between 2007 and 2018. Records of computed tomography studies were obtained from the radiology archive of a tertiary teaching hospital. The type of fracture was classified as linear, displaced, or comminuted, whereas the fracture location was classified as the manubrium, body, or xiphoid process. Results A total of 108 patients were included in the study. Of those patients, 92 (85.2%) were male and 16 (14.8%) were female. The etiology was a traffic accident in 72 cases (62.6%) and a fall from height in 36 (31.3%). The mean age was 42.1 ± 17.7 years for males and 53.9 ± 20.0 years for females. The mortality rate was 11.1%. Among the 12 deceased patients, the mean age was 44.4 ± 18.3 years. The fracture was located exclusively in the manubrium in 64 patients (59.3%), exclusively in the body of the sternum in 41 (38.0%), and in both locations in three (2.7%), whereas none were located in the xiphoid process. Morbidity rates were higher in the patients with fractures of the manubrium than in those with fractures of the body of the sternum, as was the incidence of accompanying bone fractures and organ injuries. The fracture was linear in 44 patients (40.7%), displaced in 62 (57.4%), and comminuted in 30 (27.8%). The mortality was significantly higher for comminuted fractures than for the other fracture types (p = 0.045; β = 4.40). Conclusion Fracture of the manubrium can be indicative of the severity of trauma and has a poor prognosis.


INTRODUCTION
Although fractures of the sternum account for only a small proportion of the injuries observed in patients admitted to the emergency room due to thoracic trauma, their diagnosis and follow-up are important because they can be In recent years, technological developments and higher vehicle speeds have increased the traffic accident rate. Seat belts are seen as playing an important role in that increase. Andrews et al. (4) identified fracture of the sternum as a feature of seat belt syndrome. Porter et al. (1) found that fractures of the sternum are 0.7-4.0% more common among trauma patients who were secured with seat belts than among those who were not.
Most fractures of the sternum (> 95%) are treated conservatively, because an isolated fracture of the sternum is seen as a relatively benign injury. Conservative treatment options include analgesia, rest, and passive reduction of the displacement if necessary. Surgical treatment may be required in cases of displaced fractures. Surgical fixation is indicated in case of fracture instability, displacement, or non-union (5) . Mortality rates associated with fracture of the sternum are increasing due to an increase in the frequency of accompanying findings. The associated thoracic injuries commonly encountered include vertebral fracture, rib fracture, fracture of the clavicle, fracture of the scapula, pulmonary contusion/laceration, hemopneumothorax, and mediastinal injury.
Although fractures of the sternum are described in the literature as signs of other systemic injuries, there have been, to our knowledge, no studies supporting that fact. Therefore, the aim of this study was to examine the correlations that the type and location of fracture of the sternum show with accompanying systemic findings.

MATERIALS AND METHODS
This was a retrospective study of the records of 115 patients diagnosed with traumatic fracture of the sternum between 2007 and 2018 at a tertiary teaching hospital. Computed tomography (CT) records were obtained from the radiology archive of the hospital. Seven (6.1%) of the cases were excluded because the patients were gunshot wound victims or had suffered another type of penetrating trauma. Age, sex, and mortality data were recorded. The type of fracture was categorized as linear, displaced, or comminuted, whereas the fracture location was categorized as the manubrium, sternal body, or xiphoid process. All patients underwent imaging examinations to identify any concomitant rib fractures, vertebral body fractures (with or without spinal injury), pneumothorax, hemothorax, pneumomediastinum, pulmonary contusions or lacerations, intracranial hemorrhage, intra-abdominal injuries, or vascular injuries. The CT scans had been acquired in a 256-slice multidetector scanner (Activion 256; Toshiba, Tokyo, Japan). All of the scans were examined by the same radiologists, in the volume rendering mode, as well as in the axial, coronal, and sagittal planes.
The correlations between categorical variables were examined with the chi-square test. After thus examining the variables associated with mortality, we performed a logistic regression analysis of those that were found to be significant. The correlations that the locations and types of fractures of the sternum showed with mortality and other bone fractures or systemic injuries were also tested, with univariate and multivariate analyses. The study was approved by the local research ethics committee.

RESULTS
A total of 108 patients were included in the study. Of those patients, 92 (85.2%) were male and 16 (14.8%) were female. The etiology of the fracture of the sternum was a traffic accident in 72 cases (62.6%) and a fall from height in 36 (31.3%). A summary of the findings is provided in Table 1. The mean age was 42.1 ± 17.7 years for men and 53.9 ± 20.0 years for women. Patient ages ranged from 11 years to 87 years. The mortality rate was 11.1%. Among the 12 deceased patients, the mean age was 44.4 ± 18.3 years. A summary of the findings according to the fracture location is provided in Table 2. The fracture was located exclusively in the manubrium in 64 patients (59.3%), exclusively in the body of the sternum in 41 (38.0%), and   (Table 3), the location of the fracture of the sternum (manubrium or body) was not associated with mortality, although mortality was significantly higher in patients with comminuted fractures than in those with other types of fractures [odds ratio (OR) = 4.40; p = 0.045]. When all bone fractures and other systemic injuries were included in the univariate analysis, comminuted fracture of the sternum, abdominal organ injury, and intracranial injury were found to be significant risk factors for mortality (p = 0.012, 0.003, and 0.014, respectively). However, only intracranial injury retained that significance in the multivariate analysis (OR = 9.1; p = 0.010).     Among the 108 patients with fracture of the sternum, the injury was accompanied by rib fracture in 78 (72.2%), thoracic vertebral fracture in 35 (32.4%), fracture of the scapula in 17 (15.7%), and fracture of the clavicle in 11 (10.2%). None of those additional fractures were found to be associated with mortality in the logistic regression (p = 0.449, 0.441, 0.552, and 0.852, respectively).
The most common solid organ injury accompanying fracture of the sternum was liver injury, which was seen in six patients (5.5%), followed by kidney injury, in one (0.9%), pancreatic injury, in one (0.9%), and adrenal injury, in one (0.9%). The patient with pancreatic injury also had duodenal bleeding. Abdominal solid organ injury did not correlate significantly with the location or type of sternal fracture (p > 0.05 for both).

DISCUSSION
Of all cases of thoracic trauma, 70% are caused by blunt force and 30% result from penetrating injuries (6) . In a study conducted in Canada by Hill et al. (7) , 96.3% of the cases of thoracic trauma were reported to be blunt trauma, comparable to the 95% observed in the present study.
Thoracic trauma is most common in men between 20 and 60 years of age (8) . In the relevant literature, the reported proportion of males among thoracic trauma patients is 70-80% (9) . In the present study, the mean ages of the men and women (42.1 and 53.9 years, respectively), as well as the fact that 84.8% of our patients were male, are consistent with data in the literature showing that thoracic trauma is most common in middle-aged men who are more active in life.
The morbidity and mortality associated with fractures of the sternum are mostly attributable to concomitant injuries to internal thoracic organs, and mortality rates among affected patients range from 4% to 45% (10) . The   mortality rate in our study was 11.1%, which is in keeping with data in the literature.
Some of the most important findings due to thoracic trauma are pulmonary contusion, hemothorax, and pneumothorax. In a study of patients with blunt thoracic trauma, conducted by Poole et al. (11) , the most common intrathoracic finding was pulmonary contusion, which was seen in 47% of the cases, followed by hemopneumothorax, in 27.4%. In the present study, the most common intrathoracic finding was pulmonary contusion, which was seen in 53.7% of our patients, followed by hemothorax, in 51.9%, and pneumothorax, in 53.7%.
In a significant proportion of patients, head injuries, abdominal injuries, and vertebral body fractures occur simultaneously (11) . In a study conducted by Başoğlu et al. (12) , 33.2% of thoracic trauma patients had extrathoracic injuries, 40% of which were head injuries. In another study of thoracic trauma patients, Tekinbaş et al. (13) reported that there were head injuries in 11.2% and intra-abdominal injuries in 7.0%. In the present study, 10.5% of the patients had intra-abdominal injuries and 17.4% had head injuries.
In another study of patients with fractures of the sternum, Yeh et al. (14) observed rib fractures at a rate of 69.9%, fractures of the scapula at a rate of 6.7%, and fractures of the clavicle at a rate of 11.3%, comparable to the 70.4%, 15.7%, and 11.3%, respectively, found in the present study, although we observed pulmonary contusions and fractures of the scapula at higher rates (53.7% vs. 29.5% and 15.7% vs. 6.7%, respectively). The authors attributed that difference to the recent increase in trauma severity.
In patients with fractures of the sternum, it is of utmost importance to identify the type and location of the fracture, because of the trauma-related findings. In a retrospective study of 272 patients with sternal fractures, Brookes et al. (2) found that 93.4% had a fracture of the sternal body. In another retrospective study, von Garrel et al. (15) evaluated 200 patients with sternal fractures and found that 76.5% had a fracture of the sternal body. In contrast, only 39.1% of the patients in our sample had a fracture of the sternal body. In fact, if we include the patients who had a concomitant fracture of the manubrium, that figure drops to 38.0%.
In the studies conducted by Brookes et al. (2) and von Garrel et al. (15) , linear fractures were reported to account for 47.8% and 58.0% of sternal fractures, respectively. In the present study, linear fractures were observed in only 39.1%. In their study of patients diagnosed with fractures of the sternum between 1985 and 1991, Brookes et al. (2) observed that sternal fracture was accompanied by rib fracture in 27.2% of the cases, by pneumothorax in 3.3%, by hemothorax in 5.9%, by pulmonary contusion in 3.7%, by cranial injuries in 3.7%, and by abdominal injuries in 3.3%, reporting an overall mortality rate of 0.79%. In our study, all of those rates were higher, and that difference might be attributable to the noncompliance with traffic regulations in our country and the increased trauma severity resulting from technological advances. An analysis of 1,124 victims of traffic accidents showed that the incidence of fractures of the sternum increased from 0.7% to 4.0% over a three-year period (16) . In addition, the use of seat belts increases the incidence of fractures of the sternum.
Despite the existence of various studies on fractures of the sternum, there has been, to our knowledge, no study regarding the relationship between sternal fracture location and injuries to other organs. In the present study, we found that fracture of the manubrium showed a statistically significant correlation with pneumomediastinum. It can be assumed that this relationship is due to fracture of the mediastinum together with the manubrium, with higher energy trauma than in a fracture of the sternal body, given the immediate proximity of the manubrium and its greater anatomical thickness and width. Similarly, rates of pneumothorax and hemothorax were found to be significantly higher among the patients with fractures of the manubrium. However, we found that the location of a sternal fracture did not correlate with intracranial injuries, abdominal injuries, or mortality.

CONCLUSION
Blunt trauma accounts for the majority of cases of thoracic trauma, the most common causative events being traffic accidents and falls. Fractures of the sternum typically affect the manubrium and are usually linear fractures. The rate of concomitant thoracic injuries is significantly higher in patients with a fracture of the manubrium than in those with a fracture of the sternal body, which underscores the importance of correctly identifying the fracture location. In thoracic trauma with fracture of the sternum, pulmonary contusions and rib fractures are the most common intrathoracic injuries. In addition, we detected a significant positive correlation between the type of sternal fracture and the risk of lung injury; the risk of pneumothorax, hemothorax, and pneumomediastinum increases to a significant degree when the fracture is in the manubrium. Because fractures of the manubrium occur as a result of severe trauma, additional injuries attributed to the trauma increase mortality and should be thoroughly investigated.