Anatomical study of the location of the antilingula, lingula, and mandibular foramen for vertical ramus osteotomy

Vertical ramus osteotomy (VRO) is widely used for the surgical treatment of mandibular deformity [1]. VRO is an advantageous technique in that it is less likely to damage the inferior alveolar neurovascular bundle (IANB), but if this structure is damaged, it may lead to amputation of the IANB. However, there is also a disadvantage in that osteotomy cannot be performed by directly observing the location of the IANB from the medial side of ramus [2]. For the above reasons, the anatomical location of the IANB was the most important consideration for the surgeon in performing VRO, and long-term studies have been conducted to determine anatomical reference points to prevent damage to the IANB. Many previous studies have identified the mandibular foramen, through which the IANB passes into the mandible, and the protruding anatomical structure that predicts the position of the lingula in front of the mandibular foramen, on the lateral side of the ramus; Yates named it the antilingula [3]. Several studies have since been conducted on the antilingula, lingula, and mandibular foramen [3–13].

Mandibular prognathism is a common maxillofacial deformity especially in East Asian populations, and treatment with VRO is effective in these cases [14]. However, no studies have been reported on direct measurement of such anatomical reference points in the mandibles of East Asian patients. This study attempted to locate the antilingula, lingula, and mandibular foramen by direct measurement of the East Asian mandible in order to reduce the risk of IANB injury, which may occur when performing VRO. Therefore, this study was to promote safe and accurate VRO.

Damage to the IANB during orthognathic surgery on the mandibular ramus is a major complication that can be avoided. To prevent this complication, there have been several attempts to develop novel surgical techniques to avoid damage to the IANB during osteotomy of the lateral side of the ramus, such as VRO, inverted L-osteotomy, and C-shaped osteotomy. In order to identify the theoretical basis of these surgical techniques, there have been many studies to determine the anatomical location of the IANB in the lateral side of ramus [3–6, 8–12].

The antilingula is an elevated part of the lateral side of the ramus that was previously described as a prominence [1], bump [15], or tubercle [16]. Yates et al. [3] referred to this structure as the antilingula and were the first to report a relationship with the mandibular foramen. In subsequent years, research on the antilingula was conducted as an anatomical measurement reference point for mandibular surgery. In a study by Yates et al. [3] using 70 dry mandibles, the antilingula was found in 44%, indefinitely found in 41%, and could not be found in 15%. Yates claimed that the antilingula was a highly variable anatomical landmark, but that the posterior 5~ 10 mm of the antilingula was a statistically safe area. Pogrel et al. [6] found the antilingula in all cases in a study of mandibles in 20 cadavers; in most cases, the lingula was present in the posteroinferior region of the antilingula. Aziz et al. [8] found the antilingula in all cases in a study of mandibles in 18 cadavers. The lingula was present in the anterior, posterior, superior, and inferior regions of the antilingula, but there was “no risk of damaging the neurovascular bundle” during osteotomy in the posterior 5 mm of the antilingula.

Recently, studies investigating Asian populations have also been introduced. In a study by Apinhasmit et al. [9] using 92 dry mandibles, the antilingula was found in 80.4% of the patients, and it was confirmed that the antilingula was primarily present in the anterior-inferior region of the lingula. In a study by Hosapatna et al. [12] using 50 South Indian dry mandibles, it was confirmed that the mandibular foramen existed in the posterosuperior region of the antilingula, in contrast to the findings of previous studies. In the present study, the lingula was present in posterosuperior region of the antilingula. Although the difference in the superior side was 0.54 mm, which was not significant, this was slightly different from previous studies. On the other hand, the mandibular foramen was found to be present in the posteroinferior region of the antilingula. This is a similar pattern with most existing studies.

The East Asian populations have more cases of mandibular prognathism than other races, and VRO can be useful in this case [14]. However, the anatomical studies of the mandibular ramus have been conducted mainly on Caucasian populations, and have been carried out in Southeast Asian, and Indian patients. In contrast, cases of direct measurement of the mandible in East Asian populations are not common. In this respect, the present study is meaningful.

As much as the interest in Antilingula, a controversy was raised. In a study by Reitzik et al. [4], in addition to antilingula, anatomical points termed the “midpoint of the waist of the ascending ramus” (MW) and the “midpoint of a line joining the coronoid process to the gonion” (MCG) were identified. The study reported that the MW was the most useful among the three anatomical points. Martone et al. [5] insisted that no antilingula was present and that the MW was the surgical reference point. Park et al. [11] used three-dimensional CT to study 25 patients with normal class 1 occlusion, 50 patients with mandibular prognathism, and 50 patients with mandibular retrognathism. The antilingula was clinically identifiable in 46.7, 44.4, and 45.3% of cases, and the MW was reported to be an excellent intraoperative reference point. Hogan and Ellis [17] reported that the antilingula is not an anatomical marker associated with the mandibular foramen and is not appropriate as a surgical guide for osteotomy because it is a musculotendinous apparatus. In a study by Monnazzi et al. [10] using 44 dry mandibles, antilingula was not recommended for use as a VRO landmark. In the present study, we found the antilingula in all subjects, but the use of antilingula alone as an anatomical reference point is not believed to prevent damage to the IANB.

There were several considerations when defining the anatomical measurement points in this study. In some studies, the antilingula was not observed, and it was thought that there was difficulty in setting the antilingula [3, 5, 6, 9, 12]. However, our study demonstrated that the antilingula was the most prominent part of the lateral side of the ramus, which was found by both visual and palpation methods, and was observed on both sides of the mandible (40 sites) in 20 cadavers. In the setting of the mandibular foramen, in order to safely preserve the IANB, the measurement point must be set behind the most posterior border of the mandibular foramen. However, the posterior border of the mandibular foramen is not clear. In this study, the accuracy and consistency of the measurements are maintained, as a relatively objective land mark, which is the most inferior point of mandibular foramen. The lingula was relatively clear, and there was no difficulty in setting up the point lingula.

Recently, the development of imaging technology such as CT has aided in confirming and measuring the course of the IANB in the preoperative plan [11, 18, 19]. However, in order for the surgeon to perform exactly the planned operation, it is necessary to know the accurate structure of the mandible to lower the risk of surgery, and information on the anatomical structures that can be directly observed in the surgical field are needed. Because the mandibular foramen and lingula are difficult to visually identify when performing VRO, the structure must be recognized by the surgeon. The antilingula is the most prominent part of the lateral side of the ramus and is easy to observe, even if this region does not define the exact position of the mandibular foramen, it can be highly useful as a reference point for the entire ramus.

According to the results of this study, the surgical safe region, which we propose for safe and accurate surgery in order to prevent damage to the IANB during VRO, is 29% posterior region of the total horizontal length of the ramus, 37% superior region of total height of ramus from sigmoid notch to inferior border. Numerically, this region is posterior region more than 9.02 mm from the posterior border of the ramus and superior region more than 17.86 mm from the sigmoid notch.

The current study used mandibles from only 20 cadavers; therefore, further studies will be needed in the future. Additionally, due to the different anatomical characteristics of each individual, it is important to identify the anatomy of the patient via preoperative imaging to avoid damage during surgery.

Furthermore, when the antilingula alone is used as a reference point, prevention of damage to the IANB cannot be guaranteed. However, the antilingula is still important as a reference point for the surgeon in the surgical field. By locating the antilingula in the ramus, the surgeon may be able to approximate the overall anatomy of the ramus during surgery.