Midline Mandibulotomy Approach for Oral Cavity and Oropharynx Tumors: Long-Term Experience in a Single Institution

Purpose: To describe our clinical experience with the use of the midline mandibulotomy approach for oral cavity and oropharynx tumors. Methods: Charts were reviewed retrospectively for 67 consecutive patients who underwent mandibulotomies over a 15-year period (2002-2017) as part of their treatment for oral and oropharyngeal malignancies, with an average follow-up of 57.7 months. Results: Sixty-seven patients underwent a mandibulotomy. There were 59 males (88%) with a mean age of 56.9 years and eight females (12%) with a mean age 56.5 years. The approach was a midline mandibulotomy in 50 patients (74.6%), a paramedian mandibulotomy in 10 patients (14.9%), and a posterior mandibulotomy in seven (10.44%: angle 1 (1.5%), body 5 (7.5%), and ramus 1 (1.5%). In the group of patients undergoing median or paramedian mandibulotomies, adequate exposure of the lesion was achieved in all cases with a signicant lower rate of complications (13,4%) (p<0.005) compared to the posterior mandibulotomy group (37,5%) . Conclusions: The results of the study conrm that the anterior mandibulotomy approach provides excellent exposure for oral and oropharyngeal tumors, with a signicant lower complication rate compared to the posterior mandibulotomy approach.


Background
Since its rst description in 1836 by Roux [1], different variations of the midline mandibulotomy approach for tumors of the oral cavity and oropharynx have been used. In the 1980s, based on the studies published by Spiro et al. [2,3], the midline approach was modi ed and lateral and paramedian approaches, with improved theoretical features, were adopted. Subsequent studies have analyzed the advantages and disadvantages of each approach [4][5][6].
In general, mandibular splitting is indicated for tumors of the tonsils, base of the tongue, and the retromolar fat pad, without clinical or radiological ndings of bony invasion, to provide good surgical access to the primary lesion and facilitate en-bloc resection.
This technique can be divided grossly into anterior and lateral/posterior approaches, according to whether the osteotomy is anterior or posterior to the mental foramen. A posterior mandibulotomy has several disadvantages, one of the most important being the higher incidence of osteoradionecrosis, due to the location of the osteotomy in the radiotherapy eld. In addition, the inferior alveolar nerve is often damaged, and this method gives less access than the anterior approach (4). Therefore, it has generally been abandoned. The median mandibulotomy can be further classi ed into the midline mandibulotomy between the two central incisors, and the paramidline mandibulotomy between a lateral incisor and canine.
The median mandibulotomy approach begins by designing the skin incision. Different designs have been used, none of them proven superior to others, however special attention must be taken in the lip-skin mucosal juntion in order to prevent por lip scarring.
We prefer, performing the mandibular symphysis osteotomy with a stair-case desing. A thin-saw blade with abundant irrigation is used to perform the osteotomy. The lingual cortex osteotomy can be completed by means of a chisel or a Piezosurgery Device (Mectron®) to minimize the damage to the sof tissues of the oor of the mouth.
Osteosynthesis is done by two "locking" 2.0 mm miniplates separated one from another at least 2-3 cm.
Reattachement of the genioglossal/genihioid muscles is of outmost importance.

Results
Sixty-seven patients underwent a mandibulotomy approach. There were 59 males (88%) with a mean age of 56.9 years and eight females (12%) with a mean age of 56.5 years.

Discussion
The location of the mandibulotomy in the midline offers some distinct advantages. First, it offers least disruption to the blood supply. Even though the mandibular symphysis normally has an overlapping blood supply from the inferior alveolar, lingual, and facial arteries, operative exposure often interrupts the latter two. A paramedian osteotomy forces reliance on the terminal branches of the inferior alveolar artery crossing the midline [7].
Second, since the osteotomy line is located far from the tumor, the total radiation dose to this location is lower than with lateral approaches, although a potential risk of osteoradionecrosis remains, even with the use of the new intensity modulated radiation therapy (IMRT) systems.
In our center, we try to minimize this risk using basic principles: we treat the patient's oral cavity prophylactically by extracting teeth that might be more likely to develop a postoperative infection, we use a thin saw blade to minimize the bone loss, enhancing the bone contact during osteosynthesis, we use generous irrigation during the osteotomy, and we perform internal rigid xation with at least two 2.0-mm plates, separated by 2 cm in height, with bicortical screws in the lower plate and monocortical screws in the upper one. Furthermore, pre-adapting the plates to the symphyseal region before performing the osteotomy facilitates the posterior osteosynthesis and minimizes the incidence of malocclusions.
We recommend this kind of xation for several reasons. Although some studies, like that of Amin et al. [7], recommend internal rigid xation with just one 2.3-mm plate, clinical and experimental studies examining maxillofacial trauma have demonstrated the ability of two-plate rigid xation at the symphyseal region to counteract the torsion forces generated at this point.
In our series, all the osteotomies were xed with two 2.0-mm titanium plates with at least two holes on each side of the osteotomy. In 56.6% of the cases, the upper plate was xed with monocortical screws and the lower one with bicortical screws. This allows rigid xation with a low risk of damage to the teeth apex. However, over the last 4 years we have made extensive use of plates with a lock system (43%). This also provides a rigid xation, acting as an internal xation device, and it does not require perfect adaptation to the bone.
Good bony apposition is necessary for direct bone healing. Since most of the patients will receive postoperative radiotherapy, it is important to accelerate the healing process as much as possible.
Another risk factor for the development of complications is the use of preoperative radiotherapy. Komisar et al.
[8], reported that a signi cant percentage (71.4%) of the patients who underwent a mandibular osteotomy following radiotherapy developed postoperative complications, seen as osteoradionecrosis or malunion. In such cases, this procedure should be avoided whenever possible. If indispensable, then meticulous preoperative and postoperative management of the oral status is required.
Dubner and Spiro [9], reported a 20% complication rate and Shah et al. [10] reported complications such as bone sepsis, wound sepsis, stulas, delayed union, and cases that required the removal of the wire or xation plate. By contrast, McCann et al. [11] reported that 35% of the patients in whom rigid xation was used after the mandibulotomy developed an immediate postoperative infection, osteoradionecrosis, plate exposure, plate fracture, or non-union.
In our series, the rate of complications (23.8%) was like reported rates, [12], with a greater incidence using the posterior mandibulotomy approach (20.8%).
There is no doubt that the future of oral surgery leads toward minimally invasive approaches such as the use of Robotic Surgery for base of the tongue and oro/hypopharynx tumors, [13] with less morbidity [14] . However, until this technology is not widespread, conventional techniques such as midline mandibulotomy approaches, with "modern-times" re nements, such as those described previously in the article, still have their place in head and neck oncology surgery.

Conclusions
In our experience, a median straight mandibulotomy is a safe, easy procedure with acceptable morbidity. It provides excellent exposure for oral and oropharyngeal tumors, with a low complication rate, signi cantly lower, as shown in our study, compared to the more posterior paramedian or lateral approaches.. A thin saw blade should be used to minimize the bone loss and improve the bone contact. Rigid xation with two 2.0-mm titanium plates with a lock system is highly recommended as it improves bone fragments apposition.
Until minimally invasive Robotic technology is not widespread, conventional techniques such as midline mandibulotomy approaches, with "modern-times" re nements still have their place in head and neck oncology surgery Declarations Ethics approval and consent to participate: The retrospective chart review study was approved by the Ethics Committee of the University Hospital la Paz in 2017.
Consent for publication: Consent for publication was granted by all the patients included in the study.
Availability of data and materials: The datasets used and/or analysed during the current study belong to the Oral and Maxillofacial Surgery Departmente, Universitiy Hospital la Paz (Madrid, Spain). They are available from the corresponding author on reasonable request.
Competing interests. This research received no external funding. The authors declare that they have no competing interests Funding: No funding was granted fro this study. The authors declare no con ict of interest.
All authors have read and agreed to the published version of the manuscript.