Locating the infraorbital foramen: a precision challenge for the practitioner

The infraorbital foramen (IOF) constitutes a critical anatomical landmark for infraorbital nerve blocks, maxillofacial surgery, and orbital reconstruction. As the emergence point of the infraorbital nerve, its precise localization is imperative to ensure anesthesia efficacy and prevent iatrogenic injuries during procedures on the midface. However, the individual and population-based morphological variability of the IOF often exposes practitioners to unforeseen complications or anesthetic failures.

This osteological study, conducted on 103 adult human dry skulls (representing 206 hemimaxillae), aims to precisely characterize the morphometry, bilateral symmetry, and sexual dimorphism of this region. The authors test the hypothesis that the position of the IOF is closely linked to global craniofacial morphology. The originality of this work lies in the use of standardized positioning indices and diagnostic performance analyses via ROC curves to identify morphometric predictors of accessory infraorbital foramina (AIOF). This research thus aims to provide clinically applicable reference data to secure surgical and anesthetic procedures of the facial skeleton.

Methodology: Millimeter mapping of the infraorbital region

This descriptive anatomical study focused on 103 dry human skulls (representing 206 hemimaxillae) from the collections of Mardin Artuklu University. The team included only specimens with intact maxillary anatomy, infraorbital margins, and alveolar ridges. Sex was determined through rigorous analysis of cranial morphological features, including the mastoid process, glabella, and mental eminence.

The protocol is based on a dual approach: direct measurements using digital calipers (0.01 mm precision) and digital analysis via ImageJ on standardized photographs oriented according to the Frankfort plane. The parameters evaluated include:

• Horizontal (IOF_X) and vertical (IOF_Y) coordinates relative to the Nasion (origin of the reference point).
• The diameters of the foramen and the distances to key clinical landmarks (infraorbital margin and alveolar crest).
• Global craniofacial dimensions: bizygomatic width (Zy–Zy) and upper facial height.
• The calculation of specific proportional indices: lateralization (LI), vertical position (VPI), and alveolar-orbital ratio (AOR).

Statistical analysis incorporated kernel density estimation to visualize the spatial distribution of foramina. A ROC curve analysis was also conducted to identify morphometric predictors of accessory infraorbital foramina (AIOF), identified in 18.4% of hemimaxillae. Intra-observer reliability was validated by a second survey on 20 skulls after a two-week interval.

Bilateral asymmetry and spatial coordinates

Morphometric analysis reveals significant bilateral differences regarding the spatial localization of the infraorbital foramen (IOF). Horizontal (IOF_X) and vertical (IOF_Y) coordinates, as well as the lateralization index (LI) and vertical position index (VPI), show statistically significant variations between the right and left sides. In contrast, no notable bilateral differences were observed for foraminal diameters, IOF-infraorbital rim distance, IOF-alveolar crest distance, or the alveolar-orbital ratio (AOR).

Sexual dimorphism and craniofacial correlations

Sexual dimorphism is marked by larger overall dimensions in male subjects. Male skulls exhibit significantly higher bizygomatic width, upper facial height, and FIO coordinates (horizontal and vertical) than female skulls. Conversely, females display significantly higher vertical position indices (VPI). The study establishes a strong positive correlation between overall craniofacial dimensions and the precise localization of the FIO, suggesting that the nerve's position depends directly on the patient's facial morphology.

Accessory infraorbital foramina (AIOF)

The presence of accessory infraorbital foramina (AIOF) was identified in 18.4% of hemimaxillae, with no side predominance. Analysis shows that the presence of an AIOF modifies the morphology of the main foramen:

• Skulls with IOAF present a significantly smaller vertical diameter of the main IOF.
• The distance between the IOF and the infraorbital rim is shorter in the presence of AIOF.
• The alveolar-orbital ratio (AOR) is significantly higher in these cases.

Predictive performance (ROC Analysis)

ROC (Receiver Operating Characteristic) analysis identified robust morphometric predictors for the presence of accessory foramina. The mean vertical diameter of the IOF demonstrated excellent predictive performance with an area under the curve (AUC) of 0.995. Similarly, the mean IOF-infraorbital margin distance proved to be a reliable predictor with an AUC of 0.950.

Clinical interpretation and anatomical variability

The results of this study on 103 skulls (206 hemimaxillae) demonstrate that the infraorbital foramen (IOF) is not a fixed anatomical constant, but a structure intimately linked to the facial morphotype. The significant positive correlation between craniofacial dimensions and IOF coordinates indicates that the position of the infraorbital nerve is predictable based on bizygomatic width and upper facial height. For the practitioner, this means that the planning of a nerve block or a surgical approach must systematically take into account the patient's global biometrics.

The bilateral asymmetry observed for spatial coordinates and position indices, while foraminal diameters remain symmetrical, suggests that while the size of the neurovascular passage is stable, its location may vary from one side of the face to the other. A major clinical fact emerges from this analysis: the presence of accessory infraorbital foramina (AIF) in 18.4% of cases. The study reveals that these variations are predictable: a reduced vertical diameter of the IOF and increased proximity to the infraorbital margin are robust predictors (AUC > 0.95) of the existence of an AIF, increasing the risk of anesthetic failure or iatrogenic injury.

The study's limitations include the use of dry skulls, which excludes the analysis of soft tissue thickness, and the specific geographical origin of the population. Nevertheless, the use of proportional indices (lateralization, alveolar-orbital ratio) offers a more reliable method than absolute measurements for normalizing individual variations.

Summary of results

This study conducted on 206 hemimaxillae reveals that 18.4% of the specimens present accessory infraorbital foramina (AIOF), the presence of which is highly predictable (AUC 0.995) when the vertical diameter of the main foramen is reduced. The analysis highlights a significant bilateral asymmetry in position indices, as well as marked sexual dimorphism: men present higher spatial coordinates of the foramen, correlated with their larger craniofacial dimensions.

In concrete terms, for the practitioner:

• Anticipating anesthesia failures: If the main foramen has a small diameter or is located very close to the infraorbital rim, suspect the presence of an accessory canal (AIOF) to avoid an incomplete nerve block or iatrogenic injury.
• Individualize the bilateral approach: Never assume perfect symmetry during bilateral interventions; coordinates and lateralization indices vary significantly between the right and left sides of the same patient.
• Adjusting landmarks according to gender: Integrate the fact that the foramen is proportionally lower and more lateralized in men, requiring an adaptation of the angle and depth of insertion during grafting procedures or trauma surgery.

Technical lexicon of the study

Infraorbital foramen (IOF): Terminal opening of the infraorbital canal located on the anterior surface of the maxilla, constituting the exit point of the infraorbital nerve and its accompanying vessels.

Accessory infraorbital foramen (AIOF): Anatomical variants identified in 18.4% of the hemimaxillae in the sample, the presence of which is associated with a smaller vertical diameter of the IOF and a shortened IOF-infraorbital rim distance.

Lateralization Index (LI): Proportional morphometric index used to define the horizontal position of the IOF relative to the bizygomatic width in order to normalize the measurement according to skull size.

Vertical Position Index (VPI): Standardized parameter expressing the vertical localization of the IOF relative to the upper facial height.

Alveolar-orbital ratio (AOR): Calculated index representing the proportional relationship between the IOF-alveolar crest distance and the IOF-infraorbital rim distance.

Kernel Density Estimation (KDE): Quantitative spatial mapping approach used in this study to visualize the anatomical distribution and localization probability of the IOF and accessory foramina.

ROC (Receiver Operating Characteristic) Analysis: Statistical analysis used to evaluate the ability of morphometric parameters (such as mean vertical diameter) to predict the presence of accessory infraorbital foramina.

Information intended for healthcare professionals. This content may contain errors or truncated summaries. We recommend always verifying with the original source article. Delynov disclaims all responsibility regarding the use of this information. This document is not intended for patients or the general public.