Endoscopic Medial Rectus Muscle Retraction: Comparison of Techniques to Maximize Endoscopic Exposure of the Medial Orbit

Objective: Endoscopic orbital surgery represents the next frontier in the evolution of endonasal procedures. Access to the medial intraconal space requires the atruamatic retraction of the medial rectus muscle (MRM) although techniques to achieve this vary across the literature. Here, we evaluate each of the reported methods of MRM retraction and quantify the degree of intraconal exposure conferred by each method.

Methods: A total of eight orbits from four cadaver heads were dissected to expose the medial orbits and MRM. In each orbit, the MRM was retracted using four techniques external MRM retraction at the globe insertion point using vessel loop (external group), trans-septal MRM retraction using vessel loop (trans-septal group), retraction of the MRM using vessel loop passed around the choanal (choanal loop group), and a four-handed technique using double ball retraction performed trans-septally by a second surgeon (trans-septal double ball group). The length, height, and area of exposure of the medial intraconal space were quantified and compared using Student t-test.

Results: The average anterior–posterior exposure for the external group, trans-septal group, and trans-septal double ball group was 17.51, 16.59, and 18.01 mm, respectively. The choanal group provided significantly less exposure (12.39 mm, p < 0.05), than the other groups. The average vertical exposure for the trans-septal group, choanal loop group, and trans-septal double ball group was 12.53, 13.05, and 13.57 mm, respectively. The external group provided significantly less exposure (4.51 mm, p < 0.05) than the other groups. The trans-septal and trans-septal double ball group provided the greatest total access by surface area (58.88and 62.94 mm², respectively) as compared with the external and choanal group (34.82 and 43.19 mm², respectively). The total area of exposure between trans-septal group and trans-septal double ball group was not significant. Of note, the exposure provided by the choanal loop technique was suboptimal, as it required the surgeon to work both above and below the muscle.

Conclusion: Retraction of the MRM toward the choanal provided the least length of exposure while external retraction exposed the least height and total area. Whereas there was no difference between the two trans-septal techniques, manual retraction of the MRM by a second surgeon using a double ball allows for dynamic adjustments and enhanced protection of the neurovascular inputs of the medial rectus muscle. The authors therefore advocate a four-handed approach to optimize the surgical corridor.