Study Of The Safe Place For The Retromandibular Transparotidapproach To Adults’ Subcondylar Fractures

ObjectiveThe aim of this study was to determine a relatively safe place between the inferior buccal branch and mandibular marginal branch of facial nerve, provide a reference for the retromandibular transparotid approach to adults’ subcondylar fractures, and to evaluate the safety and effectiveness of this place in clinic.Materials and methodsThis study presumed that plane of schistostoma(POS) located between the inferior buccal branch(IBB) and mandibular marginal branch(MMB) of the facial nerve in the vicinity of the posterior border of mandibular ramus, then measured and observed the positional relationships between plane of schistostoma(POS) and the inferior buccal branch(IBB), plane of schistostoma(POS) and marginal mandibular branch(MMB) on 20 unilateral adults’ cadaver heads. A safe place which located between the inferior buccal branch(IBB) and mandibular marginal branch(MMB) of the facial nerve was determined. After that in clinic, this safe place was applied to surgical treatment of 10 adults’ subcondylar fractures through the retromandibular transparotid approach.In anatomical study, plane of schistostoma(POS) was defined as horizontal plane. The lowest branch of the buccal branches crossing point with the posterior border of mandibular ramus was located as point A. The highest branch of the mandibular marginal branches crossing point with the posterior border of mandibular ramus was located as point B. The intersection of posterior border of mandibular ramus with POS was located as point C. The lowest branch of the buccal branches crossing point with the POS was located as point D.The relationships and distances between point A and POS, point B and POS, point C and point D were recoded and analyzed. According to the result of this study, a relatively safe place which located between the inferior buccal branch and marginal mandibular branch was determined.In clinical study, 10 adult patients with subcondylar fractures were treated with surgical treatment through the retromandibular transparotid approach. According to the safe place determined, the parotid tissue and masseter above the fracture line were opened to expose the fracture line. And open reduction and rigid internal fixations was then performed. The postoperative follow–up visit and curative effect evaluation of all the patients were performed at 1, 3 and 6 month after operations.ResultsIn anatomical study, the cervicofacial division located anteriorly to the posterior border of the mandibular ramus in only one case which was excluded from this study. That was because in this case, both of inferior buccal branch and mandibular marginal branch located anteriorly to the posterior border of the mandibular ramus and had no intersection with it. In the remaining and available 19 cases, point A was all above plane of schistostoma. The point B was below plane of schistostoma in 18 cases and above POS in only one case in which the plane of schistostoma was not between point A and point B. The plane of schistostoma located between point A and point B in 18 cases(90%). 3 cases existed anastomosis of the IBB and MMB in the vicinity of the posterior border of mandibular ramus.The average vertical distance from point A to POS was 9.2874mm(0.21 to 23.94 mm, SD7.21858) with a 95% confidence space(5.8081 to 12.7666mm). The average vertical distance from point B to POS was-7.0984 mm(-21.20 to 5.20 mm,SD5.97193) with a 95% confidence space(-9.9768 to-4.2200mm). The average distance from point C to point D was 14.9613 mm(0.76 to 33.33 mm, SD8.54588) with a 95% confidence space(10.2288 to 19.6939mm).In clinical study, no transient or permanent facial nerve paralysis occurred in the 10 patients. Although one patient suffered the salivary fistula and postoperative hematomas, he was healed by bandaging and intramuscular injection with atropine before meals for a week. The postoperative scars in all patients were not apparent and no patient complained of the scar. Half year postoperatively, all the patients had good recovery of mouth opening and mandibular movements. Their mouth opening was 3.4 to 4.2cm,with an average mouth opening 3.7cm. No occlusal disorder or disturbance of mastication occurred in all patients. CT showed that all the patients had good bone heals.ConclusionIn most cases,plane of schistostoma(POS) locates between the inferior buccal branch(IBB) and marginal mandibular branch(MMB) of the facial nerve in the vicinity of the posterior border of mandibular ramus. At the height of plane of schistostoma, within 1cm anterior to the posterior border of the mandibular ramus is a relatively safe place between MMB and IBB. Surgeons can safely open parotid through this place when operating subcondylar fractures by means of using retromandibular transparotid approach.