Course of the Bony Canal Associated with High-Positioned Supraorbital Foramina: An Anatomic Study to Facilitate Safe Mobilization of the Supraorbital Nerve

Objective In the dissection of the superior orbital rim, the supraorbital foramen must be released to preserve the supraorbital nerve. The aim of this study was to clarify the spatial dimensions of a high-positioned foramina to allow for the safe performance of this maneuver. Methods We examined 90 orbital sides. In the detected foramina we measured the distance between the superior orbital rim and the inferior margin of the foramen (height), and between the rim and the anterior margin of the opening of the foramen in the orbital roof (depth). To evaluate the inclination of the canal, we calculated the height:depth ratios. Foramina with a height exceeding 2.0 mm were defined as high-positioned and measurements between low- and high-positioned foramina were compared. Results We were able to find 37 foramina in 32 orbital sides; 25 (67.6%) were low-positioned and their height ranged from 0.5-1.9 mm (mean: 1.16 mm); 12 (32.4%) were high-positioned with a height ranged from 2.0-11.9 mm (mean: 4.0 mm). The depth in low- and high-positioned foramina ranged from 0.5-3.2 mm (mean: 1.44 mm) and 0.7-6.5 mm (mean: 2.13 mm), respectively. The height:depth ratio was greater in high-positioned foramina, ranging from 1.03-3.38 (mean: 2.19), than in low-positioned foramina where it ranged from 0.4-2.2 (mean: 0.98). Conclusion The height:depth ratio in high-positioned foramina, an approximate mean value of 2, and the absence of a value less than 1, was considered to indicate a steep canal inclination. To avoid postoperative forehead numbness, anatomic information regarding the course of the bony canal must be considered.