Traumatic diaphragmatic rupture due to blunt trauma tends to be severe, as it is often accompanied by various other thoracoabdominal injuries. Given that there are no characteristic signs or symptoms for its early detection, traumatic diaphragmatic rupture may be easily overlooked during initial evaluation. Delayed treatment may lead to fatal outcomes such as respiratory failure, hernia, or incarceration; therefore, the possibility of diaphragmatic rupture should be considered in the early stage of evaluation and treatment of patients with multiple trauma [12]. However, diaphragmatic rupture is known to be difficult to diagnose prior to surgery [3]. Although computed tomography has shown excellent sensitivity for diagnosing various organ injuries in the chest and abdomen, it has lesser sensitivity to diaphragmatic rupture [4]. Therefore, this study aimed to investigate the diagnostic usefulness of using the diaphragmatic height index (DHI) [5], which can be easily measured using chest radiographs alone, for diaphragmatic rupture.

In general, diaphragmatic injury is rarely diagnosed in patients with injury who are admitted to a hospital; usually, less than 10% of diaphragmatic injuries are reported [678910]. Except for penetrating wounds as a cause, right-sided diaphragmatic injury due to blunt trauma is even rarer. One study reported that the rate of left-sided diaphragmatic injury is 25 times higher than that of the right side [11]. This seems to be because the right diaphragm is protected by the liver, which is firmly fixed in place by several ligaments, while the left diaphragm is located above the stomach or spleen, which are more mobile than the liver. The rate of left and right diaphragmatic injury varies in several studies [1213]. In contrast, the frequencies of right and left diaphragm injury observed in this study were similar. This is likely because the patients were limited to those with diaphragmatic injury and diaphragmatic hernia confirmed through surgery rather than all diaphragmatic injury. A previous study on traumatic diaphragmatic injury diagnosed via autopsy also reported no difference in the frequency of left and right diaphragmatic rupture [14]. The relatively lower incidence of right-sided diaphragmatic rupture is because right-sided diaphragmatic rupture and diaphragmatic hernia are harder to diagnose than left-sided diaphragmatic injury, except when diagnosis is made via autopsy. Left-sided diaphragmatic rupture is relatively easier to determine through gastric gas patterns in the chest that can be assessed via standard chest radiography, CT, or nasogastric tube. Meanwhile, right diaphragmatic rupture is difficult to diagnose as it does not show such abnormal chest radiographic findings or distinctive clinical symptoms [81516]. CT is an important diagnostic modality in patients with thoracoabdominal injury due to blunt trauma. However, its sensitivity is relatively lower for diaphragmatic injury than that for other organ injuries [4]. Diaphragmatic injury is often accompanied by multiple organ injuries, as it is caused by a strong impact to the abdomen. Thus, performing CT before emergency surgery is sometimes impossible due to hemodynamic instability. Even if laparotomy is performed, diaphragmatic injury is sometimes not recognized until after the surgery because of the fast-paced control for hemostasis or intraperitoneal organ injuries [17]. Delayed diagnosis of diaphragmatic injury can result in sequelae that can be fatal to the patient's prognosis, such as strangulated incarceration of the gastric hernia and continuous bleeding in the peritoneal cavity, which can result in hemostasis failure [18]. Surgery is the only treatment modality for diaphragmatic injury. Hence, acquiring information in the initial evaluation or recognizing the possibility of diaphragmatic injury prior to performing emergency surgery is important for improving patient prognosis and can be helpful in preventing unnecessary repeated laparotomy.

Standard chest radiography is generally performed in the initial evaluation of trauma patients because it is fast and simple and does not require the patient to move. A simple chest radiography is mostly possible prior to surgery or upon admission even in patients who cannot undergo sufficient examinations of the entire body due to hemodynamic instability. Therefore, there have been attempts in diagnosing diaphragmatic rupture by combining simple chest radiographs and several clinical findings. One study reported that an elevated diaphragm is a strong indicator of diaphragmatic rupture [10], but it was not able to provide a standard to compare the findings of a normal diaphragm and diaphragmatic rupture other than the difference in diaphragmatic height of both sides. Furthermore, an elevated diaphragm alone based on standard chest radiography (i.e., it is not correlated with clinical findings) has low sensitivity for diagnosing diaphragmatic rupture [3]. The difference in the height of the diaphragm, that is, the right side being higher than the left side by 1.5 to 2.0 cm, has to be considered in the application of elevated diaphragm in the diagnosis of diaphragmatic rupture [19]. Moreover, the height of the diaphragm being influenced by the patient's physical condition should also be considered when using an elevated diaphragm as a marker for diaphragmatic injury. Suwatanapongched et al. [20] set the thoracic vertebrae as reference to describe the location of the right and left domes of the diaphragm. To consider the patient's physical variables, Pornrattanamaneewong et al. [5] used the height of the 10th thoracic vertebrae for calculating DHI to diagnose diaphragmatic paralysis. Because DHI is a proportional value using a simple anatomical reference, it is easy to compute and recreate. In this study, DHI was used to determine the side of diaphragmatic rupture. The mean DHI in the control group was not significantly different from that in a study by Pornrattanamaneewong et al. [5] (0.83 ± 0.5 vs. 0.6 ± 0.4), in which the control group comprised patients without chest or abdominal injuries who underwent orthopedic surgery in the extremities. Because the right diaphragm is generally higher than the left, the elevation of the right diaphragm results in a positive DHI, and elevation of the left diaphragm yields a negative DHI.

In this study, the DHI in the patients with right and left diaphragmatic rupture was significantly different than that in the control group, indicating that DHI can have a diagnostic significance in diaphragmatic rupture. The DHI cutoff values showed high sensitivity and specificity for both right and left sides. Moreover, they showed moderate reliability. However, as this study was a single-center retrospective study conducted in an Asian population, the results should be verified in other racial groups. Moreover, because all the patients in the control group did not undergo open surgery, the possibility that a small number of diaphragmatic ruptures were included was not completely ruled out. Furthermore, because an elevated diaphragm can be found in several conditions including diaphragmatic paralysis, atelectasis, thoracoabdominal tumor, subdiaphragmatic abscess, and dilation of the large bowel [21], the mechanism of injury and clinical findings must be considered when using DHI for the diagnosis of diaphragmatic rupture.

In conclusion, our findings showed that DHI computed using standard chest radiographs can be helpful in diagnosing diaphragmatic rupture. DHI as computed using chest radiographs in patients with blunt abdominal blunt trauma, particularly who are ineligible for additional diagnostic work-up such as CT, may help in the diagnosis of diaphragmatic rupture.