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Effectiveness of Computed Tomography for Blow-out Fracture

Purpose: This study assessed the association between eye symptoms (enophthalmos or diplopia) and site of damage, volume, deviated inferior rectus muscle (IRM) and type of fracture with computed tomography (CT). The intent is to anticipate the prognosis of orbital trauma at initial diagnosis. Methods: Forty-five patients were diagnosed with fractures of the inferior wall of one orbit. Fracture area, volume of displaced tissue, deviated IRM, and type of fracture were evaluated from coronal CT by one investigator. The association of those variables with the occurrence of eye symptoms (diplopia and enophthalmos) was assessed. Results: Of 45 patients, 27 were symptom-free (Group A) and 18 had symptoms (Group B) of enophthalmos and/or diplopia. In Group B, 12 had diplopia, one was enophthalmos, and five had both. By CT measurement, group A mean area was 192.6 mm2 and the mean volume was 673.2 mm3. Group B area was 316.2 mm2 and volume was 1,710.6 mm3. The volume was more influential on symptom occurrence. Each patient was categorized into four grades depending on the location of IRM. Symptom occurrence and higher grade were associated. Twenty-six patients had trap-door fracture (one side, attached to the fracture), and 19 had punched-out fracture (both sides detached). The punched-out fracture was more strongly associated with symptoms and had statistically significantly higher area and volume. Conclusion: In orbital trauma, measurement of fracture area and volume, evaluation of the deviated IRM and classification of the fracture type by coronal CT can effectively predict prognosis and surgical indication.


Introduction
Blow-out fracture of the inferior orbital wall is defined as fracture of an outer wall that supports the lower part of an orbit by the impact of blunt trauma, producing increased internal pressure [1]. Orbit damage makes up 18% to 50% of maxillofacial trauma [2]. The importance of the diagnosis to treatment of the blow-out fracture is rising because of industrialization, increasing transportation speed, and increased violent accidents [3].
For the diagnosis of orbital trauma, computed tomography (CT) is the most accurate radiologic imaging technique. Although a fracture of the orbital inferior wall was in the past often difficult to detect by two-dimensional radiography, CT allows these injuries to be diagnosed much more readily. The coronal plane of CT is especially useful for the inferior wall fracture. While CT is more accurate, there are no obvious guidelines to predict prognosis or to decide surgical repair [4]. Evaluating the location and amount of fracture with altered volume and extents of orbit provides objective indicator of a blow-out fracture.
This study assessed the association between eye symptoms (enophthalmos or diplopia) and site of damage, volume, deviated inferior rectus muscle (IRM) and type of fracture with CT. The intent is to anticipate the prognosis of orbital trauma at the early stage and provide indications to decide surgical repair.

Materials and Methods
From January 2009 to April 2014, 63 patients who came to Pusan National University Hospital with a chief complaint of orbital injury were diagnosed with orbital floor fracture. Patients with fracture of both orbits were excluded because it was impossible to measure the relative value of fragment deviation. This study included 45 patients with one-sided blow-out fracture. Of these patients, 39 were males and six were females. The mean age was 38.9 years.
Every patient underwent CT, and age, sex, cause of injury, location of fracture, and symptoms were documented in the medical record. Of the patients who underwent surgery, the following were evaluated: operating method, material, change in symptom, diplopia, and the limit of eyeball movement. Symptoms of diplopia and enophthalmos were evaluated. Enophthalmos was measured using Hertel's exophthalmometer [5]. If the difference was more than 2 mm, it was judged that patient had enophthalmos [6]. Relative value was calculated by dividing non-damaged side of orbital floor length and volume of orbit [8].  Coronal computed tomographic slices and schematics of left fractured orbits representing the muscular subscore. If the line is located just above the orbital floor, IR displacement is classified as Grade 1, the line lying on the orbital floor but more than half located inside the orbit is Grade 2, more than half of the line outside of the orbit is classified as Grade 3, and completely outside of the orbit is Grade 4 [9]. SR, superior rectus muscle; MR, medial rectus muscle; ON, optical nerve; LR, lateral rectus muscle; IR, inferior rectus muscle.

Results
Of 45 patients, 39 (86.7%) were male and 6 (13.3%) were female. The mean age was 38.5 years. The patients were sorted into two groups based on symptom status (enophthalmos or diplopia). The symptom-free group  Values are presented as median (range), number only, or number (%). Values are presented as mean±standard deviation.  (Table 3). Symptom status and higher grade were associated based on the correlation analysis in groups (P ＜0.05). Although correlation between the displacement of IRM and the area of fracture site was low, the connection with displaced volume is statistically significant. Also, both

Discussion
Surgical reconstruction of orbit wall must be considered when traumatic diplopia and enophthalmos occur.
However, because symptoms can occur not just immediately after the injury but after two or three weeks have passed, deciding whether to treat surgically is difficult [10].
Therefore, it is important to predict whether the orbit wall fracture will cause delayed eye symptoms like diplopia or enophthalmos.
Commonly used surgical indications for reconstructing the orbit wall are clinical diplopia, herniation of orbital tissue on CT image, enophthalmos more than 2 mm, and large fracture that passes over half of orbital bone [11][12][13][14].
In this study, criteria predictive of symptom status were examined using the most generalized medium for diagnosis, CT.
Manson et al. [5] insisted that the degree of enophthalmos is directly proportional to the herniated volume of orbital tissue caused by a blow-out fracture that widens the fracture area. Measuring the altered area and volume of orbital floor fracture using CT will be helpful to predict the degree of enophthalmos and to decide the feasibility of surgery.
There are many methods for measuring the volume and area of orbital floor fracture. Ploder et al. [8] found area and volume of deviated orbital tissue by measuring the width and height of fracture on coronal plane. Jin et al. [15] assumed that the deviated fragment is an oval, and calculated the area and volume of tissue fallen off by measuring width, length and height. The volume of the injured orbit can nowadays be compared with the non-affected side using three-dimensional images. In this case, the error can occur up to 7% to 8% in volume difference of both orbits and error can be made by each observer who establishes the orbit area. In this study, area and volume of fragment were calculated by adding up the length and width of bone fragments in each coronal CT image. By using this method, relative accuracy can be secured by measurement reproducibility in definite anatomical structure [16].
In this study, the association of eye symptoms with types of fracture, location of IRM, and area and volume of bone fragment measured using CT was evaluated. The findings were interpreted to mean that as deviated bone fragment area and volume of herniated tissue increase, the more symptoms occur. Also, of volume and area, volume is more strongly associated with symptom status.  [9] yielded results similar to ours. Schouman et al. [9] insisted that surgery be considered when the Grade was more than 2, and occurrence of symptoms was more frequent in Grade 3 and 4.
According to Thaller-Antlanger's research [17], type of fracture had a significant effect on prognosis, with punched-out fracture followed by orbital rim fracture predicting a poor prognosis. We found that punched-out type were less common (42%), and more related to occurrence of symptoms than trap-door type.