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International Journal of Morphology

On-line version ISSN 0717-9502

Int. J. Morphol. vol.32 no.1 Temuco Mar. 2014

http://dx.doi.org/10.4067/S0717-95022014000100052 

Int. J. Morphol., 32(1):327-333, 2014.

 

Anatomic Study of the Distance Between the Lower Margin of the Mandible and the Marginal Mandibular Branch of the Facial Nerve: A Systematic Review

 

Estudio Anatómico de la Distancia entre el Margen Mandibular y la Rama Marginal Mandibular del Nervio Facial: Una Revisión Sistemática

 

Pedro Christian Aravena*,**; Rodrigo Santibáñez**; Pablo Rubilar**; Christian Espinoza** & Francisco Pérez-Rojas***

* Institute of Anatomy, Histology and Pathology. Faculty of Medicine, Universidad Austral de Chile, Valdivia, Chile.

** School of Dentistry. Faculty of Medicine, Universidad Austral de Chile, Valdivia, Chile.

*** Faculty of Health Sciences. Medicine, Universidad Autónoma de Chile, Talca, Chile.

Correspondence to:


SUMMARY: The marginal mandibular branch of the facial nerve (MMB) has a significant variation in relation to the lower border of the mandible (LBM). That is why it is important to know its topographical description to prevent damage in submandibular surgical procedures. The objective of this study was to determine the distance between the MMB and LBM based on descriptive studies carried out on human corpses and surgical patients. A systematic review of literature in MEDLINE, "Science Citation Index Expanded" of Web of Science (ISI) databases and manual search was performed. The articles with number of samples greater than or equal to 10 facial samples and recording of measurements between the MMB and the LBM or Gonion were selected. From the selected articles, the authors registered year of publication, country of origin, number of samples, sample type (fresh, embalmed body/fixed cadavers or surgical patient), distribution percentage of the MMB in relation to LBM, average and maximum distance between MMB and LBM or Gonion. The results were presented in tables with descriptive statistic. Seventeen articles describing measurements of the distance between MMB and the lower border of the mandible carried out in cadavers and patients were selected. In these articles a total of 1,408 samples were dissected. The maximum distance observed was 4.01 cm (mean±SD 1.64±0.92 cm, Min= 0.69; Max= 4.01). Several reports suggest that an incision 2 cm below the lower border of the mandible would be enough to avoid damage of the MMB. However, according to the maximal distances registered, such an incision might involve risk for the MMB. For this reason, we propose that the MMB of facial nerve should be at least 4 cm below the lower border of the mandible.

KEY WORDS: Anatomy and histology; Facial Nerve; Facial Nerve Injuries; Surgery; Oral; Head and Neck Neoplasms; Review Literature as Topic.


RESUMEN: La rama mandibular marginal del nervio facial (RMM) posee variaciones significativas en su relación con el margen inferior de la mandíbula (MIM), siendo importante su descripción topográfica para evitar su daño en procedimientos quirúrgicos submandibulares. El objetivo fue determinar la distancia RMM y MIM observadas en humanos. Se realizó una revisión sistemática de la literatura en las bases de datos MEDLINE, "Science Citation Index Expanded" de Web of Science (ISI) y una búsqueda manual. Se seleccionaron artículos con análisis de 10 o más muestras y que registraran la distancia entre el RMM y el MIM o Gonion. Se registró autor, países de origen, condición de la muestra, número de muestras, distancias promedio y máximas registradas. Los resultados se analizaron mediante estadística descriptiva y presentada en tablas. Se seleccionaron 17 artículos con mediciones de las distancias entre el RMM y MIM tanto en cadáveres como pacientes. En total, 1,408 muestras fueron disecadas. La distancia máxima registrada fue de 4.01 cm (promedio±DE 1.64±0.92 cm, Min= 0,69; Max= 4,01). Diversos reportes sugieren que una incisión a 2 cm bajo el margen inferior de la mandíbula sería suficiente para evitar el daño al RMM. Sin embargo, con las distancias máximas observadas dicha incisión podría generar un daño. Por lo tanto, esta revisión sugiere la presencia del RMM a lo menos a 4 cm bajo el margen inferior de la mandíbula.

PALABRAS CLAVE: Anatomía; Nervio Facial; Cirugía Oral; Cirugía Maxilofacial; Cuello; Revisión sistemática.


 

INTRODUCTION

The marginal mandibular branch (MMB) originates in the facial nerve and is responsible for providing motor innervation to the circumoral musculature, which is primarily responsible for lip expression (Batra et al., 2010). Due to its location, this branch can be damaged during cervical surgeries and particularly in surgeries confined to the submandibular region (Wang et al., 1991), such as fixation of mandibular angle fractures (Cabrini Gabrielli et al., 2003), parotidectomies (Barry et al., 2007; Mra et al., 1993), submandibular gland excisions (Milton et al., 1986), carotid endarterectomies (Aldoori & Baird, 1988; Assadian et al., 2004), rhytidectomy and liposuction surgery (Liebman et al., 1988). It can be also damaged during the deep dissection of the neck (Nason et al., 2007).

The classical approach in these procedures is to use the Risdon's technique or submandibular approach: an incision of 4-5 cm long and 2 cm below and posterior to the angle of the mandible (Ebenezer & Ramalingam, 2011). The most common cause of paralysis of this nerve is due to iatrogenic damage during surgery in the mandibular or parotid regions (Batra et al.; O`Brien, 2007; Toure et al., 2004; Woltmann et al., 2006). Its damage can cause salivary incontinence and aesthetic impairment due to an alteration in the balance of the musculature around the lower lip, in its lateral, downward and inversion movements (Moffat & Ramsden, 1977). These complications are difficult to correct (Stern, 1992). However, in most cases it may be temporary, with a recovery time that ranges from 3 to 6 months after surgery (Nason et al.).

The high incidence of injury to the MMB may be related to the proportionally greater number of operations in the region of the mandible (Dingman & Grabb, 1962), but also to the lack of an accurate description of the course of this nerve in the anatomical textbooks (Moore, 1985; Williams et al., 1995).

According to Suazo & Manterola (2010), it is possible to evaluate a number of morphological topics through systematic review of the literature. Therefore, the aim of this work was to determine the distance between the MMB and Lower Border of Mandible (LBM) based on descriptive studies carried out on human corpses and surgical patients, and then to propose a suitable length for surgical access of the neck.

MATERIAL AND METHOD

A systematic review of literature was performed according to the PRISMA statement reporting guideline (Moher et al., 2010). Research was carried out taking into consideration anatomical and surgical descriptive studies that recorded the distance between MMB and LBM or Gonion on cadavers or patients. Articles reviewed were published between 1960 and 2013, in English, and available in electronic databases Medline by PubMed (http://www.ncbi.nlm.nih.gov/pubmed/) and "Science Citation Index Expanded" of Web of Science of Thomson Reuters (ISI) database (www.webofknowledge.com) on January 10th, 2014. In addition, a manual search of the biomedical literature available in the Central Library from Universidad Austral de Chile was performed. The search strategy is summarized in Table I.

After collecting the data, according to search strategy, two authors (RS and PR) read the publication's abstracts and titles, discarding papers that did not meet the following search criteria: number of samples greater than or equal to 10 facial samples and recording of measurements between the MMB and the LBM or Gonion.

From the selected articles, the authors registered year of publication, country of origin, number of samples, sample type (fresh, embalmed body/fixed cadavers or surgical patient), distribution percentage of the MMB in relation to LBM, mean and maximum distance between MMB and LBM or Gonion. Furthermore, the degree of bias in the selected articles was presented qualitatively by including the anatomical points upon the measurements that were made.

In those articles where the authors (RS and PR) had discrepancies in the classification/collection of data, a consensus was reached qualitatively by assessing the article by a third author (PA). Consequently, the data found were tabulated and summarized in Table II. The results were analyzed with the statistical software STATA 10.0, using descriptive statistics.

Table I. Keywords and limits used by database.

Table II. Name of authors, country, sample conditions and measurement landmark between
the Marginal Mandibular Branch of Facial Nerve (MMB) and Lower Border of Mandible (LBM) of each articles selected.

RESULTS

Sixty-one articles were obtained from the electronic databases and 3 articles from the manual search of the literature. Those with duplicates in the databases, which did not meet the selection criteria and the articles that lacked full text, were excluded. In total, 17 articles were selected for further analysis (Fig. 1).

These articles were published between 1962 and 2013 and around 50% of them were from Asian origin. The data were collected from 1,121 cadavers and 287 patients. The measurements were made from different anatomical points, being the lowest point of the arc of the nerve the most used. The extreme landmarks were the facial artery and Gonion, anteriorly and posteriorly, respectively. The name of authors, country of origin, sample condition and measurement landmarks used in each report are summarized in Table II.

The average maximum distance between MMB and LBM was 1.5±0.74 cm (min = 0.69; max = 4.01) (Table III).

Fig. 1. Flow chart of literature review and selection criteria.

Table III. Number of samples and distances between MMB and LBM of each articles selected.

DISCUSSION

In this revision, the highest value between the MMB of the LBM was 4.01 cm (Karapinar et al., 2013) and 3 cm was found (Nason et al.; Wang et al.). Most of the researches used attached bodies, but an important number of samples (n=287) were patients (Nason et al.; Balagopal et al., 2012). The selected articles demonstrated, also, the variation of the position and itinerary of the facial nerve according to if the dissection of the neck were conducted in neck extension and neutral position. In addition, they indicated that the measurements on neutral position were the lowest for distances between the MMB and the LBM. Wang et al., have the third largest number of cases studied (n=120) showed an average of 0.95 cm, and 4.34% of the cases have a range between 2.1 and 3 cm. Moreover, an average of 50% was observed regarding the course of the MMB below the LBM. Finally, an average of 50% showed the course of the MMB below the LBM, which has a range that fluctuates from 15% to 100% (Basar et al., 1997).

Possible explanations to the variations of the distances measured by the authors include the position of the head when making the measurement (Nason et al.) and also the state of the cervical tissues, since in fresh corpses samples or living patients with lax connective tissue, the MMB can be found as low as 3-4 cm from the LBM (Moffat & Ramsden) versus fixed corpses samples whose tissues contract and stiffen. There may be differences in the measurements inherent to the volume by dehydration in human corpses (Nason et al.) and edema in surgical patients with greater relevance in those cases showing a traumatic lesion.

Surgical practice has divulged, through texts and surgical atlas, the dissection measures known as the Risdon technique, corresponding to an incision of 2 cm below the LBM (Toure et al.). To achieve this distance the authors propose to mark a projection of one (Dingman & Grabb) or two (Ziarah & Atkinson, 1981; Cranin, 1975; Ellis & Zide, 1995; Potgieter et al., 2005) finger width below the LBM. At the time this review was carried out, we observed other recommendations as varied as making the incision at a distance of at least 1.6 cm from LBM and Gonion (Batra et al.), 2.1cm (Karapinar et al.) and 3 cm or more (Wang et al.; Woltmann et al.; Savary et al., 1997; Kim et al., 2009; Zani et al., 2003).

The limitations of our study were also considered: articles were recovered from only 2 databases Science Citation Index Expanded via Web of Science and MEDLINE only over the decade from 1961 to 2013 year. We excluded reports in languages other than English, as well as studies in which it was impossible to perform a meta-analysis due to the nature of the data. Despite these limitations, the articles analyzed included those in which a direct clinical or anatomical assessment of distance between MMB of the LBM was performed, excluding studies with other points of measurement for to compare the results between reports. However, because of the diverse measurements found, as well as the lack of homogeneity in their definitions and the measurement methods used, the inclusion of other papers, from other databases,in other languages, would produce even more diffuse results.

Although the number of articles and samples studied could provide a clear distance from the MMB to the LBM, the methodology used is not comparable between articles. They differ in their geographical origins, type of samples, sex, variability in the number of collateral branches (Dingman & Grabb; Basar et al.; Savary et al.; Kim et al.; Balagopal et al.) and the anatomic landmarks chosen for the measurements. These are all elements that can generate and increase variations in the results and, therefore, difficulty when comparing them. The different methodologies that were used to obtain the results in these articles and the lack of statistical methods, did not allow scientific analysis to determine a reliable distance. Thus, to understand if the variability of the observed measurements corresponds to the real situation or if it is an artifact of different methodologies, a statistical design is needed.

In view of what has been said so far, the distance parameter (2 cm) based on what has been described by anatomy and surgical textbooks, is ambiguous and can be misleading. Likewise, there are reports that indicate that an incision between 3 to 4 cm below the LBM (Wang et al.; Savary et al.; Kim et al.; Zani et al.), is sufficient to avoid consequent damage to the MMB. Hence, to establish its clinical validity, the surgeon must be extremely careful.

As a conclusion, and based on the data found throughout this systematic review, we propose that the MMB of facial nerve should be at least 4 cm below the lower border of the mandible.

We recommend that an incision of at least 3 cm parallel to the LBM should be made, adding a safety margin higher than 1 cm based of maximum distance looked in report of Karapinar et al. Thus, the concomitant damage that may affect the MMB, causing neurologic sequelae, can be avoided, even if it means increasing the difficulty of the surgical technique.

ACKNOWLEDGMENTS. We are thankful to Miguel Reyes, Carolina Vergara and Günther Preisler for having kindly fully reviewed and comments to this paper. This paper is based on a thesis submitted in partial fulfillment of the requirements for the degree of Bachelor in Dental Surgery in the School of Dentistry of the Universidad Austral de Chile.

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Correspondence to:

Pedro Aravena

Faculty of Medicine
Universidad Austral de Chile
Campus Isla Teja s/n Valdivia
CHILE
Phone: 56-63-221205

Email: paravena@uach.cl

Recibido : 10-06-2013
Aceptado: 23-01-2014