Comparison of degree of medial rectus muscle misalignment after medial orbital wall decompression with or without periosteal flap

Purpose To compare the degree of postoperative medial rectus (MR) muscle misalignment in patients who underwent medial orbital wall decompression with or without a periosteal flap along the MR muscle. Methods This retrospective, observational study included 40 sides from 26 patients. The following parameters were measured on axial computed tomographic images taken post- and/or preoperatively: the distance of the anteroposterior line between the posterior lacrimal crest and the junction of the ethmoid and sphenoid sinuses from the most medial point of the medial margin of the MR muscle; the angle created at the point of the MR globe insertion, the most medial point of the MR muscle, and the junction of the ethmoid and sphenoid sinuses; and the MR muscle cross-sectional area. Postoperative changes in the distance (MR muscle shift) and area (MR muscle expansion) were calculated, and MR muscle shift, MR muscle angle, and the rate of MR muscle expansion were compared between the groups with (22 sides) and without (18 sides) a periosteal flap. Results MR muscle shift (P = 0.325), MR muscle angle (P = 0.219), and the rate of MR muscle expansion (P = 0.904) were not significantly different between the groups. Conclusions Preservation of the periosteum along the MR muscle is thought to prevent MR muscle misalignment after medial orbital wall decompression. However, the results of this study indicate that preservation of a periosteal flap may not contribute to lessening MR muscle shift after surgery.