Determination of a safety zone for transbuccal trocar placement: an anatomical study

Abstract

The identification of a safe and accurate technique for facial incisions for transbuccal approaches to the mandibular angle fractures remains a challenge. An alternative method of safely and accurately placing the buccal skin incision is described in this cadaveric study. Thirty-two dissections were performed on 16 bilateral embalmed adult cadaveric heads. In order to identify a safety zone for transbuccal trocar placement, a triangle shaped zone created by three lines was determined. The branches of the facial nerve in this zone were reflected by sharp and blunt dissections. Of 32 sides, marginal mandibular branch was encountered in 1 and marginal mandibular branch and buccal branch of the facial nerve were found in 2 of the predetermined triangle. In 29 of 32 specimens, the marginal mandibular branch was encountered out of the triangle and deep to the platysma muscles. The triangle determined in the present anatomosurgical study presents an easy identifiable and safe zone for trocar placement.

Transbuccal trocar placement is widely used for drill placement and fixation in the reconstruction of mandibular angle fractures and stabilization of the mobilized segments during sagittal split ramus osteotomy procedures. In both cases, a small extra-oral stab incision was given to permit the insertion of a transbuccal canula. Location of the extra-oral stab incision was guided by the location of the fracture line and the position of the facial vessels and facial nerve.

The transbuccal approach is usually advocated because it results in no external scarring and allows direct visualization and conformation of the desired occlusion during placement of the bone plates. Despite the advantages of this approach, it has been suggested that transbuccal trocar technique has limitations. Transbuccal trocar placement is technique sensitive and the surgeon has to be familiar with the armamentarium and be skilled in the use of the trocar canula.

In the literature, there is some controversy about identifying a safe and accurate technique for transbuccal incisions. It has been suggested that the surgeon’s inexperience will lead to additional facial incisions, especially when access is severely limited due to the nature of the masseteric region, and that there is a risk of damaging the facial nerve.

In order to overcome the problems regarding the identification of an ideal safety zone for transbuccal placement, an alternative method of safely and accurately placing the buccal skin incision is described in this cadaveric study.

Material and methods

This study was based on 32 dissections performed on 16 bilateral embalmed adult cadaveric heads from body donation to the Anatomy Department of the Gulhane Military Medical Academy. There were 14 males and 2 females of undetermined age. None of the cadavers had any clinical evidence of previous mandibular or facial trauma, surgery, tumour, or any other maxillofacial pathologic features.

The cadavers were used after obtaining the appropriate consents and approvals. All methods for securing human tissue were humane and complied with the tenets of the Declaration of Helsinki.

In order to identify a safety zone for transbuccal trocar placement, a triangle shaped zone created by the following three lines was determined ( Fig. 1 ). Line 1 (trago-basal line) ran from the tragus to the groove over the body of the mandible at the antero-inferior angle of the masseter (the course of the facial artery on the body of the mandible). Line 2 (cantho-gonial line) ran from the outer canthus to the angle of the mandible (gonion). Line 3 (mandibular line) was the border of the mandible.

Fig. 1
Line 1 (trago-basal line): tragus to the groove over the body of the mandible at the antero-inferior angle of the masseter (the course of the facial artery on the body of the mandible). Line 2 (cantho-gonial): outer canthus to the angle of the mandible. Line 3 (mandibular line): the border of the mandible.

Dissections of the triangles on 32 preserved Caucasian cadaver sides were completed by the two primary investigators (A.G. and C.K.). All measurements were confirmed by both investigators. In preserved cadaver heads with overlying skin, the lines were marked with surgical pens and the overlying skin on the borders of the triangle between these three lines was incised and removed. The nerves in this zone were reflected by sharp and blunt dissections. Undermining was carried on until individualizing the superior and inferior buccal branches and the marginal mandibular branch of the facial nerve. During nerve dissection, the branches were not separated from underlying tissues. The skinless cadaver heads were dissected in the same manner after determination of the triangle.

Results

Of 32 sides, the marginal mandibular branch of the facial nerve (MMBFN) was found in 3 of the predetermined triangles. The course of the MMBFN in each case was as follows. In the first case, the MMBFN entered the triangle through the corner between the trago-basal line and cantho-gonial line, crossed the triangle inferiorly and left it at an angle of 90° to the mandibular line. The buccal branch of the facial nerve (BBFN) was encountered adjacent to the corner between the trago-basal line and the cantho-gonial line ( Fig. 2 ). In the second case, the MMBFN entered the triangle through the inferior third of the cantho-gonial line, and passed out of the triangle through the distal third of the mandibular line ( Fig. 3 ). In the third case, the MMBFN ran parallell to the inferior border of the mandible (Line 3). Two buccal branches entered the triangle through the upper third of the cantho-gonial line passing out of the triangle through the upper third of the trago-basal line and anastomosing with the MMBFN anterior to the triangle ( Fig. 4 ).

Fig. 2
(A) The facial nerve on the right side (lateral view). (B) Marginal mandibular (M) and buccal (white area) branches of the facial nerve in the triangle.

Fig. 3
(A) The facial nerve on the left side (lateral view). (B) Marginal mandibular (M) branch of the facial nervee in the triangle.

Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Determination of a safety zone for transbuccal trocar placement: an anatomical study
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