Localization of The Infraorbital Foramen with Reference to Facial Bony Landmarks: The Predictive Method And Its Accuracy

Abstract

The infraorbital nerve (ION) provides sensation around mid‐face and the ION block is used for regional anesthesia in many procedures. Therefore, the location of infraorbital foramen (IOF) and accessory infraorbital foramen (AIOF) where the ION and its branches exit through is important. Although, many studies tried to identify the location of the foramen using facial landmarks, the results varied and some of them were not applicable in practice. This study aims to find the relationship between IOF and AIOF, predict the location of IOF with reference to anterior nasal spine (ANS) and the lowest point of the zygomaticomaxillary junction (Z) which are palpable both in bone and soft tissue surface and assess an accuracy of the proposed predictive method.A total of 216 dry skulls were examined. Specimens with facial distortion were excluded. Live images of skull were analyzed by Leica Application Suite Core V4.12. The anatomical position of IOF and AIOF was observed. The line between ANS and Z (A) was the main reference line. For localization of IOF, the vertical distance from IOF to line A (B) and ratio of the distance from ANS to the intersecting point of line B with line A (D) to distance A (D:A) were measured. Statistical analysis was conducted to analyze the statistical difference between sex and sides with a significance level of 0.05. Accuracy assessment was determined in 15 cadavers. To find the predicted IOF in cadaver, measured from ANS for the length of predicted distance D which was calculated by multiplying the average distance A of cadaver with the average D:A of skulls and then measured above that point for the length of average distance B of skulls. Distance between the predicted IOF to the exact IOF was measured.There were 86 AIOFs in skulls. Most of them located superomedial to IOF except for 3 AIOFs which located in the inferolateral position. The mean distance between IOF and AIOF was 7.47 ± 2.70 mm. The location of IOF was predicted by the mean distance B and the mean ratio D:A which were 15.14 ± 1.99 mm and 63.35 ± 3.9%. No statistically significant difference was found between sex and sides (p>0.05). In cadavers, mean distance error of the predicted IOF was 1.10 ± 1.44 mm lateral and 0.59 ± 1.39 mm inferior to the exact IOF. There were 50% of predicted IOFs which accurately located within the exact IOF. From the results, clinicians can apply this predictive method in performing the ION block by palpating bony prominence of ANS at the uppermost part of philtrum at the level of nostrils and Z at the lowest bony prominence of cheek, then measure about medial two‐thirds of the line between ANS and Z and measure above the line for 15 mm where IOF is suspected to be.The predictive method for localization of IOF by using ANS and Z as reference points has the mean distance error of 1‐2 mm which is small and might not be discriminated by palpation. Moreover, there were 50% of the predicted IOFs locating within the exact IOF.Therefore, this study provides an alternative method for localization of IOF which could be useful in performing more effective and safer ION block. For further consideration, assessing the accuracy of this method in real patients and comparing with the standard method should be considered.