Using fixed anatomical landmarks to avoid medial rectus injury: a radiographic analysis in patients with and without Graves' disease.

Background: Injury to the medial rectus (MR) is a potentially devastating complication of orbital and sinus surgery. Precise knowledge of the MR relative to the lamina papyracea (LP) is important during endoscopic surgery for both Graves' ophthalmopathy and inflammatory disease. The objective of this study is to determine the location of the MR in relation to easily identified and frequently encountered intranasal landmarks in patients with and without Graves' disease.
Methods: High-resolution computed tomography scans were analyzed in 100 controls and 63 patients with Graves' disease. The MR position was recorded relative to the maxillary sinus ostium (MSO), anterior ethmoid artery (AEA), and posterior ethmoid artery (PEA)/horizontal basal lamella (BL). Clinically relevant variables recorded at each level included the Keros stage, AEA position, MR height, and distance of the MR to orbital floor, skull base, and LP.
Results: The mean distances between the MR and LP were statistically different for both groups. Controls at the MSO, AEA, and PEA/BL were 2.92, 1.69, and 1.06mm; for Graves' patients measurements at these sites were 2.12, 1.20, and 0.029mm. When comparing the two groups, each of these distances were statistically significant (p<0.02). There was no difference in ethmoid cavity width (p>0.05) between controls (9.66mm) and Graves' patients (9.70mm). Sex, age, and skull base depth were not statistically significant factors.
Conclusion: This study illustrates the position of the MR from the perspective of an endoscopic surgeon utilizing fixed intranasal landmarks. Knowledge of the position of MR is critical to safely perform decompression surgery and when operating adjacent to the LP during endoscopic surgery.
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