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. 2021 Jun 12;239(4):782–787. doi: 10.1111/joa.13482

The relative locations of the supraorbital, infraorbital, and mental foramina: A cadaveric study

Kathylin M Hester 1, Omid B Rahimi 1, Constance L Fry 2, Haley L Nation 1,✉
PMCID: PMC8450472  PMID: 34120334

Abstract

The purpose of this study is to investigate the applicability of the current surgical guideline stating that the main facial foramina that transmit cutaneous nerves to the face (supraorbital notch/foramen, infraorbital foramen, and mental foramen) are equidistant from the midline in European and Hispanic populations. Previous studies suggest this surgical guideline is not applicable for all ethnicities; however, to our knowledge, no data have been published regarding the accuracy of this guideline pertaining to the Hispanic population. An experimental study was performed on 67 cadavers donated to the Human Anatomy Program at UT Health San Antonio. The supraorbital, infraorbital, and mental foramina were dissected and midline structures including the crista galli, internasal suture, anterior nasal spine, and mandibular symphysis were identified. The distance from each foramen to midline was recorded using a digital caliper. For all cadavers/ethnicities studied, the supraorbital, infraorbital, and mental foramina were 25.32 mm, 29.57 mm, and 25.55 mm to the midline, respectively. Thus, the infraorbital foramen is located significantly more lateral compared to the supraorbital (p < 0.0001) and mental foramina (p < 0.0001). After dividing the sample based on ethnicity, this relationship was also true for the European sample and tended to be true for the Hispanic sample. Significant anatomical variations exist in the current surgical guideline stating that the supraorbital foramen, infraorbital foramen, and mental foramen are equidistant from the midline. Clinicians may need to adjust their methodology during surgical procedures of the face in order to optimize patient care.

Keywords: cutaneous innervation, face, facial foramen, infraorbital foramen, mental foramen, supraorbital foramen

This manuscript expands on the clinically practiced guideline suggesting the supraorbital, infraorbital, and mental foramina are equidistant from the midline. It is the first article to examine this anatomical relationship in the Hispanic population. Our data suggests that clinical practitioners should adjust their current anatomical landmarks in this population of patients to improve patient outcomes.

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1. INTRODUCTION

Skeletal landmarks can be used to palpate underlying structures and the relationship between different skeletal landmarks can be used to create surgical guidelines. Knowing where particular skeletal landmarks are located and where they are in relation to one another is critical for surgeons to decrease the risk of injury to vital nerves, arteries, and veins that are traversing them. The commonly held convention is that the supraorbital notch/foramen (SONF), infraorbital foramen (IOF), and mental (MF) foramina are located on the same sagittal plane, thus equidistant from the midline. For the scope of this study, the SONF, IOF, and MF are being collectively referred to as “cutaneous facial foramina” because these foramina transmit nerves that supply general sensation to the skin of the face.

This surgical guideline is used by clinicians who administer nerve blocks to anesthetize the area surrounding these cutaneous facial foramina. Examples of clinicians who may use this guideline includes, but are not limited to, plastic surgeons, ophthalmologists, dentists, and oral maxillofacial surgeons. The guideline works with the assumption that through palpation of the SONF, one can quickly approximate the location of the IOF and MF for nerve blocks during dental or facial procedures and surgeries. The current literature suggests there is sufficient variability between previous publications to warrant a thorough investigation of the SONF, IOF, and MF (Agthong et al., 2005). Even more importantly, there is evidence to suggest there are ethnic variations in the location of the facial foramina (Agthong et al., 2005; Chung et al., 1995; Gupta, 2008; Lim et al., 2016; Zhang et al,l.,l.,l., 2019). Previous reports suggest that race and ethnicity may influence the position of the SONF, IOF, and MF; thus, the current surgical guideline may be specific to certain races and ethnicities. A study of dried skulls of a North‐West Indian population stated that in 80% of the skulls the SONF, IOF, and MF were on the same vertical plane (Gupta, 2008). However, studies analyzing these same foramina in Korean and Sri Lankan populations found that for a majority of subjects studied each foramen was not equidistant from the median plane (Agthong et al., 2005; Chung et al., 1995; Gupta, 2008; Lim et al., 2016). It should be noted that only 38.1% of the Korean sample and 7% of the Sri Lankan sample had SONF, IOF, and MF equidistant from the midline (Chung et al., 1995; Nanayakkara et al., 2016). Thus, within the same Mongoloid race, ethnicity appears to influence the accuracy of this skeletal guideline. To our knowledge, no data have been published regarding the applicability of this surgical guideline to the Hispanic population.

2. MATERIALS AND METHODS

Sixty‐seven adult male and female cadavers donated to the Human Anatomy Program at UT Health San Antonio were used for this study. As a member institution of the State Anatomical Board of the State of Texas, UT Health San Antonio utilizes body donors for education and research and follows accepted national guidelines. No IRB approval was required as the project was deemed not regulated research. (Protocol Number: HSC20180149N).

Cadavers used in this project were previously dissected by dental and medical students over the 2017–2019 academic years. The cadaver population studied consisted of 28 females and 39 males; the average age of all cadavers was 81 (min =52 years, max =98 years). Age, ethnicity, and cause of death were recorded anonymously from family and funeral reports. Only cadavers who were either Hispanic or European were included in the study. Reasons for exclusion from the study were edentulous mandibles and skulls in which the bony landmarks of interest were not intact. The SONF, IOF, and MF had been previously dissected by medical and dental students, but these foramina and adjacent areas were intact and thus further dissected. The crista galli, the internasal suture, the anterior nasal spine, and the mandibular/mental symphysis were identified. Soft tissue surrounding or obscuring these skeletal features were dissected and removed to allow full view of these structures.

In order to establish a visible midline, a string was placed connecting two or more of these aforementioned midline structures, that is, crista galli, internasal suture, anterior nasal spine, and mandibular/mental symphysis. Because the horizontal and vertical diameter of the SONF, IONF, and MF varies, measurements were taken to the center of each foramen. Pins were placed in the center of both the left and right SONF, IONF, and MF. The head of the pin was placed at the same level (height) as the string so that the perpendicular distance from the foramen (represented by the pinhead) to the median plane (as established by the midline structures) was being measured. Measurements were taken using a Mitutoyo Precision digital caliper recording to the nearest hundredth of a millimeter.

3. RESULTS

Measurements of all cadavers studied, regardless of sex, side of the face, and ethnicity, were recorded. The SONF (n = 134) had a mean distance of 25.3 ± 3.9 mm to the midline; the IOF (n = 134) had a mean distance of 29.6 ± 4.4 mm to the midline; and the MF (n = 134) had a mean distance of 25.6 ± 3.0 mm to the midline (Figure 1). The difference in the distances to midline between two foramina was also noted. The variability in the horizontal position of the IOF from the midline compared with the SONF was significant, varying from 0.07 to 19.21 mm. Other studies have demonstrated similar variability (Chrxanovic et al., 2011; Nanayakkara et al., 2016). The lateral deviation of the IOF is significant; in fact, 13.6% of the sample (18/132 sides; bilateral in n = 1 cadaver) had a distance between the SONF to midline and IOF to midline that measured greater than 10 mm. The greatest lateral distance between the SONF and IOF in a single cadaver was 19.21 mm. The variability in the horizontal position of the IOF from the midline compared with the MF ranged from 0.04 to 16.09 mm. This variability between the SOF and MF measurements were within 0.00 to 17.04 mm of each other. Paired sample t tests found a statistically significant difference (p < 0.0001) between the SONF vs. the IOF distances to midline, and a statistically significant difference (p < 0.0001) between the IOF vs. MF distances to midline (Figure 1). There was no statistically significant difference (p = 0.5730) between the SONF vs. MF distance to midline.

FIGURE 1.

FIGURE 1

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Foramina distances to midline for all cadavers

Subgroup analysis of European (n = 128) and Hispanic (n = 6) cadavers was performed (Figure 2). For the European sample (n = 128), there was a statistically significant difference (p < 0.0001) between the distance from the SONF to midline and the IOF to the midline. Likewise, this distance differential was found between the IOF distance to the midline (p < 0.0001) and between the MF distance to the midline. There was no statistically significant difference (p = 0.5730) in the SONF distance to midline versus the MF distance to midline. For the Hispanic sample (n = 6), there was no statistically significant difference between the SONF and the IOF distance to the midline (p < 0.5610), between the IOF and the MF distance to the midline (p = 0.3677), or between the SONF and the MF distance to midline (p = 0.7708).

FIGURE 2.

FIGURE 2

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Foramina distances to midline based on ethnicity

To determine if ethnicity has any influence on the skeletal relationship being studied, an unpaired two‐sample t test compared the cutaneous facial foramina distances between the European (n = 128) and Hispanic (n = 6) samples. There was no statistically significant difference between the European vs. Hispanic sample in regards to the SONF distance to midline (p = 0.9500; 25.33 ± 3.8 mm vs. 25.23 ± 6.0 mm, respectively), IOF distance to midline (p = 0.3244; 29.65 ± 4.3 mm vs. 27.83 ± 5.9 mm, respectively), and MF distance to midline (p = 0.4358; 25.51 ± 2.9 mm vs. 26.49 ± 4.6 mm, respectively). In conclusion, there was no statistically significant difference when comparing cutaneous facial foramina distances between European and Hispanic populations.

A three‐way analysis of variance (ANOVA) with a 95% confidence interval was performed to determine how the three cutaneous facial foramina distances to the midline are affected by location on the left or right side of the face and the sex of the cadaver. Regarding the distance between the SONF, IOF, and the MF and midline, there was no statistical difference between the left and right sides of the body. While there was no difference between sexes for the SONF and MF, there was a small statistically significant difference for the IOF distance to midline (p = 0.0486) between sexes on the right side of the body (R male 30.23 ± 3.9 mm vs. R female 26.55 ± 4.6 mm) but not the left (Figure 3).

FIGURE 3.

FIGURE 3

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Foramina distances to midline for all cadavers based on sex and side of the face

4. DISCUSSION

It is generally accepted that the SONF, IOF, and MF are equidistant to the midline (Miller, 2005). The SONF is palpable clinically as a small depression within the supraorbital rim of the frontal bone; thus, palpation of the supraorbital notch is typically performed to estimate the horizontal location of both the IOF and MF (Beer et al., 1998). This surgical guideline is used by clinicians who administer nerve blocks to anesthetize the area surrounding these cutaneous facial foramina. However, this guideline was not reproduced in the South Texas population in this study; the average distances from these foramina to the midline were 25.3, 29.6, and 25.6 mm, respectively (Figure 4). On average, the IOF (29.6 ± 4.4 mm) is 4.3 mm lateral compared to the SONF (25.3 ± 3.9 mm) and 4.0 mm lateral to the MF (25.6 ± 3.0 mm). When applying an IOF nerve block, a 4.0 mm or 4.3 mm difference may not be clinically significant due to the diffusion properties of the anesthetic. However, the lateral‐most extent of the infraorbital foramen is clinically important. In 13.6% of cadaver sides, the IOF was >10 mm lateral to the SOF and the MF. In one cadaver, the distance was actually 19.21 mm. It is unlikely that anesthetic solutions can diffuse these greater distances. Knowing that a significant proportion of the population (13.6% of sides) has a significant lateral deviation (>10 mm) of the IOF may require clinicians to inject anesthetic more laterally to completely anesthetize the infraorbital nerve.

FIGURE 4.

FIGURE 4

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Traditional vs. proposed model

In addition to a significant lateral deviation of the IOF, other anatomical factors may influence the adequacy of nerve block anesthesia. Previous literature has reported the prevalence of an accessory IOF in 7.4%–47.6% of the population (Canan et al., 1999; Nanayakkara et al., 2016; Polo et al., 2019; Rai et al., 2013; Zhang et al., 2019). Our study did not find any accessory SOF or IOF likely because our study was performed on cadaver heads rather than skulls. It is possible that minute accessory foramina were present but obscured by other tissue. These accessory foramina may also lead to incomplete anesthesia after a nerve block.

Other studies have also found variability in the accuracy of the surgical guideline based on race and ethnicity (Agthong et al., 2005; Chung et al., 1995; Gupta, 2008; Lim et al., 2016; Zhang et al., 2019). For example, a deviation from the accepted standard had been reported in the Asian population. Chung et al., (1995), in a Korean study of cadavers, reported the average distance to midline for the SONF, IOF, and MF was 22.7, 27.2, and 24.4 mm, respectively. Agthong et al., (2005) reported that in a study of Asian skulls, SONF, IOF, and MF distances to midline were 24.4, 34.1, 28.0 mm for the right side and 25.1, 34.3, and 27.8 mm for the left side, respectively. Lastly, Gupta (2008) reported that for a North‐West Indian population (n = 79), the SONF was 23.9 mm from midline, IOF was 28.4 mm, and MF was 25.8 mm. Our finding that the IOF was on average 4.3 mm lateral compared to the SONF and 4.0 mm lateral compared to the MF demonstrates that this variation occurs in the South Texas population of Europeans as well.

When comparing each ethnicity to the surgical guideline, there was a statistically significant difference between the guideline and the European sample. The IOF was significantly more lateral compared to the SONF and MF. However, there was no statistically significant difference between any of the cutaneous facial foramina measurements for the Hispanic sample. This may be explained by our small Hispanic sample size (n = 6) or it may be an ethnic variation; thus, more research on Hispanic individuals should be conducted before any conclusive statements regarding this population can be made.

Lastly, the interaction between side of the face and sex on these cutaneous facial foramina was studied. The side of the face and sex had no effect on the cutaneous facial foramina measurements except for one; the distance from the right IOF to midline in males was slightly (and significantly; p = 0.0486) greater than that of females. This small difference in sexes is likely an anomaly as other publications have shown sex to have no impact on the horizontal location of the IOF (Nanayakkara et al., 2016). Other literature suggests that facial features and foramina positions are greater in males compared to females; our data, however, do not support any major sex‐difference (Chrcanovic et al., 2011). This discrepancy in the literature over the impact of sex on the facial foramina locations may be attributed to different population characteristics.

The authors recognize several limitations to this study, including family‐reported ethnicity in the absence of genetic testing and a low sample size of Hispanic individuals. The Willed Body Program for UT Health San Antonio receives donations from the San Antonio area and within a 100‐mile radius. According to the 2010 US Census, 63.6% of the San Antonio population identifies as Hispanic (U.S. Census Bureau Quick Facts). However, based on family‐reported ethnicities, the Willed Body Program only receives on average three Hispanic cadavers per academic year. The age of the cadavers is an additional limitation of this study. The age of the cadavers in this study ranged from 52 to 98 and the average age was 81 years old. Numerous studies of the aging face have shown increased bone deposition in the forehead and supraorbital rim while bone resorption occurs in the inferior orbital rim and midface (Medelson et al., 2012). It is not clear how these bony changes affect the relative positions of the SONF, IOF, and MF. Some studies have suggested that with age the facial foramina have been noted to move more laterally; thus, age may have affected the measurements taken in this study (Mendelson et al., 2012). Currently, there are no published data on the anatomy of the Hispanic skull. Therefore, despite these limitations of using family‐reported ethnicities, the Hispanic sample size, and the age of the cadavers, the data within this study is significant for the future treatment of this population.

Substantial variation in the facial foramina locations exist between cadavers; this is critically important for clinicians when they perform infraorbital nerve blocks and surgical dissections in reconstructive and aesthetic surgery in the midface. While many studies have demonstrated the IOF lying lateral to the SONF (Agthong et al., 2005; Chrcanovic et., 2011; Chung et al., 1995; Dixit et al., 2014; Gupta, 2008; Nanayakkara et al., 2016; Tezer et al., 2014) to the authors knowledge, this is the first study to demonstrate a lateral deviation of >10 mm in a significant proportion of the population (13.8%). When performing infraorbital nerve blocks clinicians may want to use a greater volume of anesthetic, penetrate the skin more lateral, or use an agent that increases tissue diffusion to reach a greater surface area. This is the first report to investigate the skeletal landmarks and facial foramina locations in the Hispanic population. We found that the assumptions regarding the anatomical location of the IOF, like many other ethnicities, requires modification in the European and Hispanic South Texas population.

AUTHOR CONTRIBUTIONS

Kathylin M. Hester, MS, contributed to the concepts and design of this study and collected, analyzed, and interpreted the data. She also drafted and critically revised the manuscript. Omid B. Rahimi, PhD, contributed to the concepts and design of this study. He assisted in collecting data by gathering family‐reported ethnicities; he also approved this article. Constance L. Fry, MD, contributed to the concepts and design of this study and also approved this article. Haley L. Nation, PhD, contributed to the concepts and design of this study and collected, analyzed, and interpreted the data. Dr. Nation assisted in critical revision of this manuscript and approved the article.

ACKNOWLEDGEMENTS

The authors would like to thank the body donors for their contributions to education and research.

Hester, K.M., Rahimi, O.B., Fry, C.L. & Nation, H.L. (2021) The relative locations of the supraorbital, infraorbital, and mental foramina: A cadaveric study. Journal of Anatomy, 239, 782–787. 10.1111/joa.13482

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author, HLN, upon reasonable request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author, HLN, upon reasonable request.

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