Anthropometric Analysis of Infraorbital Foramen in Adult Indian Dry Skull

Introduction

The infra orbital foramen (IOF) is situated on the anterior surface of maxilla about 1cm below the infra orbital margin (IOM) bilaterally. Infra orbital vessels and nerves emerge out through IOF¹. The Infra orbital nerve (ION) is a continuation of maxillary division of trigeminal nerve. It is entirely sensory in nature. It emerges out from IOF after passing through infra orbital canal and appears on the face. It terminates by dividing into palpebral, nasal and labial branches to supply skin over the lower eyelid, conjunctiva, lateral aspect of external surface of nose, upper lip, ala of the nose and the premolar teeth. Infra orbital vessels are branches of maxillary artery which supplies the area surrounding IOF². Large variations in the location of IOF have been reported by many authors with regard to the different landmarks on the skull varying from 4-12mm³. Knowing the exact location of IOF is very important for giving local anesthesia in maxillofacial, plastic surgeries and radio ablative neurotomy procedures⁴. Zygomatic complex fractures are one of the most common facial injuries which involve ION^{5, 6}. In these cases, earlier the surgical intervention, more the recovery of the nerve injury⁷. A major factor that inhibits dentists from using the ION block is the fear of injury to the patient's eye³. Since there are very few studies done on the Indian population, the present study was undertaken.

Materials and Method

Sixty adult dry skulls of unknown sex were collected from the department of Anatomy. Those skulls with damaged foramen or fractures were excluded from the study. All the measurements were done in millimetres using a digital vernier caliper (Mitutoyo Corp, Japan) with an accuracy of up to 0.1 mm.

After placing the skull in anatomical position, the distance between superior parts of the rim of the IOF to IOM (DIM) in sagittal plane was measured (Fig. 1) and the distance between the medial parts of the rim of the IOF to lateral margin of the pyriform aperture (DIP) was measured in the horizontal plane (Fig. 1). All the readings were taken and the mean of the two were calculated on right and left side separately. All the measurements were tabulated and statistically analyzed for significance.

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Fig. 1

Measurements a) Distance between IOM and rim of IOF (A) b) Distance between PA and rim of IOF (B).

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Results

The mean DIM on right side was between 3.2 mm to 10.42 mm and 2.6 mm to 10.1 mm on the left side (Table 1). The mean DIP on right side was between 10.1 mm to 22.7mm and 8.3 mm to 23.1 mm on the left side. There was no statistically significant difference in the mean DIM & DIP between the right and left side.

Discussion

On comparison of mean DIM between the present and previous studies it was observed that the mean DIM was less than all the other studies. The data listed in the table. 2 are done in different regions and populations, like Brazil, India, Thailand, Egypt and different ethnic groups in New York. The studies done on Thai skulls⁸ and different ethnic groups in New York⁴ shows higher value than rest of the others. Our value is comparable with all the studies done in the region of Brazil^{9, 10, 11, 12,} and India^{2, 3, 13, 14} except a study done in southern part of India⁶ which shows higher value compared to our study.

On comparison of the mean DIP of the present study with the previous studies, it was observed that the mean DIP of the present study was higher when compared to the data obtained by Elias MG et al.⁹ and Rajani Singh¹³ and lower when compared to the studies by HS Shaik⁶ and Macedo VC et al¹⁰.

Lokanayaki, 2013 distance between rim IOF and PA, authors have shown quite wide variation ranging from 13 mm to 18 mm (Table. 3). Here the data listed in table. 3 are obtained from different geographical areas like Turkey, Brazil and India. In this our value is 16.67mm which is comparable with one of the Indian study¹⁴.

The present results of this study provide valuable information to assist the maxillofacial surgeon to locating the infraorbital nerves and vessels. This will help to avoid damage to these structures¹⁵. Previous studies of different researchers have shown that distance between rim IOF and IOM are quite variable which are listed in table. 2. There are many surgical procedures are done over the maxilla such as rhinoplasty, Caldwell-Lucoperations, tumor surgery, reduction of the orbitalfloor (blow-out) and malar fractures, and the LeFort I type osteotomies may result in an iatrogenic injury to ION. Even in trigeminal neuralgia of second division knowledge of exact location of ION is essential to inject neurolytic solutions^{16, 17}.

The closest estimation of the location of the IOF should be used when designing access incisions to the orbital floor and rim and planning regional nerve blockade. However presence of multiple IOF should be kept in mind. Study quotes that higher frequency of multiple foramina was noted in Mexicans^{4, 18}.

Nerve localization for this block ideally relies on a landmark-based approach using palpation of the foramina. However, occasionally it can be challenging to identify each foramen by relying on palpation alone. In these cases, many experts search for the foramina by gently probing with a small-gauge needle. Ultrasound imaging is a safe simple non-invasive modality through which soft tissues and nerve structures can be visualized and identified when combined with a thorough knowledge of regional anatomy¹⁹.

Infra orbital nerve blocks are performed in children for management of postoperative pain associated with cleft-lip surgery and endoscopic sinus surgery. The main aspect in determining the placement of the needle is to locate the IOF and to access the nerve through an intraoral route or through a transcutaneous route²⁰.

ION sensory disturbances are diagnosed based on patients¹ symptoms, which includes hyperalgesia or hypoalgesia of the skin. Hyperalgesia was diagnosed in 11.9% of patients and hypoalgesia in 52.5%of patients⁵. Hu SH et al., described the areas supplied by the different branches of ION²¹.

Locating and preserving the infra orbital neurovascular bundle can be difficult with a comminuted fractureof the anterior maxillary wall and inferior orbital rim. The data show only small significant differences between males and females. Therefore, knowledge of the distance from the inferior orbital rim may be valuable in identifying the danger zone of its location during dissection of these fractures as well as during other surgical procedures¹⁵.

Studies conducted in different geographical areas showed a large dispersion and variability in the various distances pertaining to the location of the IOF due to different osteoblastic and osteoclastic activity in different individuals¹³.

Conclusion

Thus, the data obtained in this study is at par with studies conducted by different authors of various geographical areas. So the information derived here in identifying the precise location IOF will help surgeons to reduce the adverse outcome of the surgeries centered on IOF in patients of Indian origin. This information is also useful for morphologists who conduct their research on people of different populations and geographical regions.