Safety of Silastic Sheet for Orbital Wall Reconstruction

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Abstract

INTRODUCTION

An orbital blowout fracture is caused by a sudden increase in the intraorbital pressure in the orbit followed by a severe impact on the orbit. The purpose of orbital reconstruction is to restore the orbital volume and the shape of the orbital cavity with autogenous or alloplastic materials [1]. There can be many complications after orbital reconstruction, including infection, hematoma, nerve injury, diplopia, extraocular muscle limitation, enophthalmos, and sensory change [2,3].

Most surgeons think that the choice of implant material may contribute significantly to the long-term result of orbital reconstruction [4]. Recently, expensive materials, such as Medpor and absorbable meshes, have been used frequently for orbital wall reconstruction in order to minimize complications. In our department, silastic sheets are often used for the reconstruction of orbital fractures because they are extremely cheap and seem to cause relatively few complications. Some patients insist on the use of a silicone sheet because of its low cost. Therefore, until recently, we have used silastic sheets for orbital fractures.

The purpose of this study is to compare the complication rates of patients reconstructed with silastic sheets with those of patients reconstructed with other implant materials in the case of small orbital wall fractures.

METHODS

Four-hundred and sixty-one patients who presented with orbital wall fractures between March 2001 and December 2012 were included in this study. Among them, a statistical analysis was performed on the data of the 431 patients whose fracture size was less than 300 mm². All patients underwent primary surgical treatment. The patients were analyzed for age, sex, fracture type, preoperative symptoms, inserted material, and postoperative complications. Data from these 431 patients were analyzed retrospectively using electronic databases.

Diagnosis and treatment were based on physical examinations and computed tomography (CT) scans of the orbit in the axial and coronal images. The orbital fracture size was calculated by using the collected coronal and imaging data. For each slice, the length of the orbital floor was measured, and by applying the known slice thickness, the area of the orbital floor and medial wall could be calculated [5]. The calculated fracture size was the cross-sectional area of the fracture. Cases in which the fracture size was less than 300 mm² were included in this study.

Orbital reconstruction was performed in the acute phase (within 2 weeks). A subciliary approach was used in most of the cases of inferior orbital wall fractures. Further, medial orbital wall fractures were repaired through a medial eyebrow incision. By subperiosteal dissection, orbital implants were inserted below the periosteum. After orbital reconstruction, a forced duction test was conducted to confirm that the implant catches the orbital content. All patients received intravenous antibiotics preoperatively and postoperatively.

Postoperative facial bone CT was routinely performed 3 days after surgery. When ocular symptoms occurred after surgery, the postoperative CT scan was obtained as soon as possible. When there was hematoma with a volume effect or implant migration on the postoperative CT scan, revisional surgery was performed immediately. The follow-up period was 3-12 months; symptoms such as diplopia, limitation of eyeball movement, sensory change, and infection signs were checked, and exophthalmometry measurements were conducted. Revision surgery was performed in patients with prolonged diplopia, eye movement limitation, and prominent enophthalmos.

All statistical analyses were performed using PASW ver. 18.0 (SPSS Inc., Chicago, IL, USA). Fisher's exact test and logistic regression were used for the analyses. A multivariable analysis was performed along with the logistic regression analysis. P<0.05 was considered to be statistically significant.

RESULTS

Four-hundred and thirty-one patients with orbital wall fractures were enrolled in this study during a 12-year period. The average patient age was 31 years; 337 of these patients were male, and 94 were female. Among the 431 cases, 355 cases were pure orbital wall fractures (82.4%), and 76 were combined with zygomatic fractures (17.6%).

Of the 431 patients, reconstruction with silastic sheets was conducted in 129 patients (29.9%). Titanium meshes were used in 238 patients (55.2%), and absorbable meshes were used in 64 patients (14.8%) (Table 1).

Table 1.

Choice of materials

Thirteen patients required revision surgery because of postoperative diplopia, extraocular muscle limitation, enophthalmos, and hematoma. The overall revision rate was 3.0%. Seven patients with silastic sheet implants required revision surgery. The revision rate of the silastic sheet group was 5.4%, and that of the titanium mesh group was 1.7% (Table 2).

Table 2.

Revision rate by materials and fracture size

When the revision rate was classified by fracture size, the revision rate was higher when the fracture size was larger. However, there was no statistically significant difference among the three groups (P=0.693, Fisher's exact test) (Table 2).

When the revision rate was classified by the type of orbital fracture, the revision rate did not differ statistically by fracture type (P=0.573, Fisher's exact test). Two hundreds and seventy-eight patients had an inferior orbital wall fracture, and the revision rate was 3.2% (9/278). One hundred nine patients had a medial orbital wall fracture, and the revision rate was 3.7% (4/109). Forty-four patients had inferior and medial orbital wall fractures simultaneously, and none underwent revision surgery.

Among the 431 patients analyzed, there were 355 pure orbital wall fracture cases, and the revision rate was 3.4% (12/355). Seventy-six cases combined with zygomatic fracture, and the revision rate was 1.3% (1/76). There was no statistically significant difference among these groups (P=0.480, Fisher's exact test).

There was a trend toward surgeons' selecting titanium as the orbital implant material when the fracture was relatively large. There was a statistically significant difference among the three groups in this case (P=0.037, Fisher's exact test; P for trend=0.003) (Table 3).

Table 3.

Materials used according to the fracture size

In the multivariable analysis, fracture size and implant material were included as variables. When the variables were adjusted, the odds of revision after silastic sheet insertion were 3.65 times higher compared with the titanium insertion (P=0.043, odds ratio=3.65; 95% confidence interval, 1.04-12.83) (Table 4). The larger the fracture size was, the higher was the odds ratio, but these findings were not statistically significant.

Table 4.

Relationship between underlying condition of patient and revision rate

The cases of complications that needed re-operation are listed in Table 5. The immediate postoperative complications were diplopia, extraocular muscleslimitation, hematoma, and implant malposition. These complications were resolved with re-operation. A delayed complication that needed revision in most cases was enophthalmos.

Table 5.

Complications that needed re-operation

DISCUSSION

In the case of a large defect, calvarial bone grafts and titanium meshes have been successfully used as orbital implants [6]. In the case of relatively small defects, alloplastic implants have been used effectively. Each alloplastic material has its own advantages and disadvantages. The ideal implant should not increase the operative complication rate; it must be durable, pliable, biocompatible, and cost effective.

Silastic sheets are relatively inexpensive and easily available. However, past studies have pointed out that they have a high complication rate. Problems include infection, migration, and extrusion of the implant, along with intraorbital squamous epithelial cyst formation [7 ,8]. Titanium is very biocompatible and is easily molded and stabilized. However, titanium meshes firmly adhere to the periorbital tissue [9]. This interaction can result in extraocular motility restriction, eyelid retraction, and a difficulty in removing the implant when a second operation is required. Absorbable implants provide sufficient strength for supporting the orbital tissue until the implant resorbs in the body. After new orbital bone formation, an absorbable implant resorbs. Therefore, there are advantages of low risk of extrusion and low risk of late infection. However, exact data regarding the resorption rate and time are not available.

The result of orbital wall reconstruction using silastic sheets is controversial. Morrison et al. [7] conducted a review of 311 patients with silastic implants and found that 41 patients (13.2%) required implant removal. Their reasons for the removal of implants were infection, pain, extrusion, and diplopia. Yun et al. [10] conducted a review of 115 patients reconstructed with silastic sheets. Six patients (4.3%) needed implant removal due to infection, hematoma, displacement, or extrusion, with a mean removal time of 23.3 months. These complications were associated with a delayed inflammation response; therefore, the authors insisted on using alternative materials. On the other hand, Prowse et al. [11] conducted a review of 58 patients with silastic sheets. Of these, 4 patients needed revision due to extrusion and infection, but compared with other groups reconstructed with other materials, there was no significant difference in the revision rate. Therefore, they concluded that reconstruction with silastic sheets can still be used for orbital fracture reconstructions.

Our study analyzed the difference in revision rate when the defect size was less than 300 mm² by orbital materials such as titanium meshes, silastic sheets, and absorbable meshes. We excluded the cases in which the fracture size was more than 300 mm². When the revision rate was analyzed in subgroups of fracture size 0-100 mm², 100-200 mm², 200-300 mm², and 300-400 mm², the revision rate was increased sharply when the fracture size was over 300 mm². When the fracture size was more than 300 mm², the revision rate increased to about 20%. There were 30 cases in which the fracture size was more than 300 mm². 22 out of these 30 cases were reconstructed with titanium meshes. Surgeons tend to select a titanium mesh as an orbital implant when the fracture size is large (P=0.022, Fisher's exact test). Because the selection of titanium mesh dramatically increased when the fracture size was more than 300 mm², the results of the statistical analysis could be confusing. The cause of the high revision rate could be misinterpreted as the use of titanium mesh, but in fact, the high revision rate was due to the severity of the fracture. This in turn increases the revision rate for the cases reconstructed with titanium meshes. The fracture size seems to be the greatest risk factor for revision irrespective of the materials used for reconstruction in the case of large fractures, as per the multivariable analysis. Therefore, we excluded the cases of large fractures (more than 300 mm²).

A limitation of this study is that Medpor was not used in this study, although Medpor implants are among the most widely used implants in orbital reconstruction. Surgeons in our hospital did not selected Medpor because of their personal preferences. We found that the revision rate was higher when the orbital fracture was reconstructed with a silastic sheet than when with any other material even in the case of small defects. Silastic sheets have advantages of low price and cost-effectiveness but have a higher revision rate than that in the case of any other materials. Considering the cost, discomfort, and efforts of secondary revision surgeries, it is appropriate to use alternative materials such as absorbable meshes or titanium meshes instead of silastic sheets.

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