Surgical treatment of enophthalmos using an endoscope and T-shaped porous polyethylene fabricated with a mirror image

Abstract

Enophthalmos is corrected mostly through reducing the enlarged orbit volume by identifying intact bone edges and spanning the defect with an implant or autogenous graft. Predicting the amount of volume which must be added to correct enophthalmos is not easy using this method, and the outcome may be unsatisfactory. In this study, the authors examined 9 patients in whom enophthalmos was caused by a defect or inadequate surgery of the orbital medial wall. The authors designed an adequately shaped implant by using the mirror image obtained before surgery, and prepared a T-shaped Medpor for each patient in order to maintain the accurate contour of the medial wall and to decrease the enlarged orbital volume. During the surgery, the T-shaped Medpor was inserted while monitoring the posterior portion of the orbital wall. Satisfactory results were obtained for all the patients. Although the new method of implant design developed by the authors in this study is limited to the reconstruction of the medial wall, it is considered useful for the surgical treatment of posttraumatic enophthalmos because it takes into account both the contour and volume of the orbital wall.

Post-traumatic enophthalmos is defined as a discrepancy between the orbital contents and bony volume. Post-traumatic enophthalmos occurs particularly frequently after orbital medial wall injury because the fractured medial wall is vulnerable to damage, but this condition is not easy to diagnose and treat. The medial wall is paper-thin, and it can experience symmetric compression type fractures. Medial orbital wall fractures may be ignored and, as the support structure grows weaker over time, the eyeball can be displaced to the posterior portion. The unique structure of the medial wall makes orbital reconstruction difficult, and the risk of injuring the optic nerve and the eye globe poses an added obstacle.

Enophthalmos is corrected mostly through reducing the enlarged orbit volume by identifying intact bone edges and spanning the defect with an implant or autogenous graft. Predicting the degree of exophthalmos is not easy using this method, and the outcome may be unsatisfactory.

Recently, computer-assisted surgery including stereolithographic modelling, and individually generated titanium meshes for mirrored-reconstruction have been reported to improve the accuracy of fracture reduction and orbital reconstruction.

The authors fabricated T-shaped porous polyethylene (Porex Surgical Inc., Newnan, GA, USA) for 9 post-traumatic enophthalmos patients before surgery by predicting the adequate contour, size and shape of the orbital wall using a mirror image to correct enophthalmos accurately. The authors placed the porous polyethylene in the accurate position for reconstruction, by monitoring the medial wall and the inferior wall with the use of an endoscope during surgery.

The purpose of this study was to evaluate a new method for the correction of post-traumatic enophthalmos.

Materials and methods

9 consecutive patients who were treated at the authors’ hospital from September 2009 to December 2011 were included in this study. All patients provided written informed consent and the institutional ethical committee approved the study. The guidelines of the Declaration of Helsinki were followed in this investigation.

The time between injury and treatment varied from 2 months to 2 years. Patients included 6 men and 3 women, ranging in age from 20 to 45 years, with a mean age of 31 years. The follow-up observation period ranged from 6 to 30 months (average, 18.4 months).

Enophthalmos was caused by a car accident in 4 patients, violence in 4, and a fall in 1. Three patients had an orbital wall fracture that had not been treated and 6 had received surgery at another hospital or at the authors’ hospital. Of the 6 patients who had undergone prior treatment, 4 received surgery for zygoma fracture and the orbital wall and 2 received orbital wall reconstruction.

A computed tomography (CT) scan including axial, coronal and 3 dimensional (3D) bone reconstruction was performed before surgery. An ophthalmologic examination was also performed before surgery.

3D CT was performed, for all patients, and the result was reversed between left and right on a computer by mirroring so that the affected side became the unaffected side and the unaffected side became the affected side. Based on the 3D model Mimics (Materialise’s Interactive Medical Image Control System, Materialise, Belgium) prepared in this manner, titanium mesh (M-TAM) (from Howmedia Leibinger GmbH & Co. KG, Freiburg, Germany) was built according to the contour and size of the medial wall of the unaffected side. Using the shape of the titanium mesh as a guide, the authors prepared a T-shaped Medpor (porous polyethylene) to be used in surgery. Figure 1 depicts the design of the T-shaped Medpor in which the 3 sheets are referred to as A, B and C. Sheet A fits the contour and size of the medial wall, B plays the role of reinforcing support by connecting the medial wall and the inferior wall, and C, overlaps with A, and supports the medial wall and increases the volume effect of implant. Titanium mesh was not used directly in orbital reconstruction, but played the role of a guide in shaping the porous polyethylene because titanium is convenient for preparing shapes in advance.

Fig. 1
T-shaped Medpor design and surgical technique.

Under general anaesthesia, a subciliary incision was made in all patients. The orbicularis oculi muscle was separated and detached up to the inferior orbital rim along the septum. The periosteum of the inferior orbital rim was resected and herniated soft tissue was restored inside the orbit.

An endoscope was used during placement of the porous polyethylene ( Fig. 2 ). This allows the Medpor to be placed accurately on the position to be reconstructed, and optic nerve injury can be prevented by monitoring the posterior portion of the orbital wall. Fixation with screws or sutures was not required.

Fig. 2
(A) Intraoperative endoscopic image. The arrow indicates the medial wall defect. (B) The Medpor was prepared in a T shape using 3 sheets. (C) Orbital wall reconstruction using the T-shaped Medpor. The arrow indicates the medial wall.

Results

The authors measured the degree of enophthalmos from the same zygomaticofrontal process base to the posterior surface of the lens in each orbit, and enophthalmos was the normal distance minus the traumatized eye distance ( Fig. 3 ). The patient who did not properly achieve zygoma reduction was excluded from the study. Enophthalmos was measured by the same examiner using axial CT scans obtained before and after surgery ( Figs 4 and 5 ). All the postoperative CTs were taken at least 1 month after surgery.

Fig. 3
Measurement of the degree of ocular protrusion. The position of each globe was measured from the zygomaticofrontal process baseline to the back of the lens. (A) The degree of enophthalmos was 5.43 mm before surgery. (B) Enophthalmos was improved after surgery.

Fig. 4
Axial CT scans at the same height. (A) Preoperative view, left enophthalmos was 2.61 mm. (B) Postoperative view, enophthalmos was improved.

Fig. 5
(A and B) Photos before surgery showed enophthalmos and hypophthalmos on the left side. (C and D) The photos reveal good facial symmetry and globe projection after surgery.

Before surgery, the mean was 4.04 mm. After surgery, 7 patients had good globe projection (≤1 mm), and 2 patients had mild enophthalmos (≤2 mm) ( Table 1 ). Acceptable results were achieved in all patients, with a decrease in the degree of enophthalmos to less than 2 mm. Late complications did not occur and the results were stable and aesthetically excellent 6–30 months after the surgical procedure ( Fig. 6 ).

Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Surgical treatment of enophthalmos using an endoscope and T-shaped porous polyethylene fabricated with a mirror image
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