The Posteroinferior Sub-Parotid Incision (PISP) Approach for Subcondylar Fractures: A Cadaveric Study

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Conclusion: The oral and maxillofacial surgeon is often asked to clinically assess injuries of the face based on both physical and radiographic exam. The purpose of this study was to assess the percentage of ZMC fractures that underwent open vs. closed repair at the University of Iowa Hospitals and Clinics. As a result of the standard use of CT imaging in diagnostic work-up, many facial injuries including ZMC fractures that are diagnosed, never require surgical intervention. Based on the infor- mation gathered approximately 42% of the cases re- viewed underwent surgical treatment and 58% did not with only observation required. Almost 86% of the pa- tients reviewed were male with a mean age of 37. The breakdown for mechanism of injury included 29% motor vehicle crash, 21% assault, 17% falls, 8% motorcycle crash and 25% other. Statement of the Problem: Subcondylar fractures are common in maxillofacial trauma. Their management remains controversial, with proponents for both closed and open treatment depending on the functional and esthetic considerations. Common extraoral approaches for surgical management require dissection through the parotid gland or place the facial nerve and surrounding vascular structures at risk of injury. The objective of this study was to perform a cadaveric study to demonstrate an alternative technique for the open management of subcondylar fractures and identify the anatomical layers and structures encountered in this approach. Materials and Methods: Dissection of cadavers was conducted utilizing the PISP approach, with the anatom- ical layers encountered, the access provided and the relationship of great auricular nerve (GA) and facial nerve trunk (FNT) to common landmarks quantified. These measurements were recorded by 2 separate ex- aminers with a Cen-Tech 6-inch electronic digital cali- per. A measurement from the apex of the mastoid pro- cess to the GA as it crosses the anterior border of the sternocleiodomastoid muscle (SCM) was recorded. Also, the distance of the FNT with the mandible in repose (incisors 1 cm apart at the incisal edges) to the posterior edge of the mandible angle (A) was obtained. A vertical measurement from the most posterior and inferior as- pect of the angle of the mandible to the superior border of the zygomatic arch (B) was also recorded. Methods of Data Analysis: Data collected was re- corded, calculated and analyzed utilizing Excel. A total of 29 embalmed cadavers were dissected. Results of Investigation: A total of 58 sides were dissected, with four being excluded due to previous parotid gland surgery and/or damaged tissue. The PISP approach was performed following Langer's lines, with a 3-cm incision made posterior to the ramus, along the ante- rior border of the SCM and paralleling the angle of the mandible. In all specimens, the superficial layer of the deep cervical fascia was dissected down to the SCM, the GA identified and protected, the tail of the parotid gland iden- tified and reflected antero-superiorly. Superior retraction of the gland and overlying soft tissue allowed proper access to the sub-condylar region in all specimens. The facial nerve was not encountered in any of the dissections. The GA visualized in all specimens provided a dissection guide towards the tail of the parotid and the anterior branch didn't need to be divided to provide surgical access. The GA was found to be at a mean distance of 2.71 cm on the left and 2.99 cm on the right from the apex of the mastoid process. The FNT bifurcation was found to be at a mean distance of 3.92 cm from the posterior angle of the mandible (A). Measurement from the posterior angle to the superior border of the zygo- matic arch (B) showed a mean of 7.23 cm, with the FNT found vertically and posterior to the mandible at an average of 53.7% of this distance. Conclusion: Chossegros first described a retroman- dibular approach for access to the mandible by lifting the tail of the parotid. This cadaveric study shows that the PISP approach provides a safe and easily reproducible approach to the subcondylar region with minimal to no risk to neurovascular structures.