Is injury to the inferior alveolar nerve still common during orthognathic surgery? Manual twist technique for sagittal split ramus osteotomy.

The osteotomy in a bilateral sagittal split ramus osteotomy (BSSRO) is made in close proximity to the inferior alveolar nerve (IAN), so direct damage to the nerve and irreversible neurosensory deficit may result. The aim of this study was to compare the incidence of injury to the nerve when a conventional osteotomy using an osteotome was made, with that after manual twist splitting. We retrospectively reviewed the casenotes of 769 consecutive patients who had bilateral SSRO either alone or with a simultaneous maxillary procedure by a single surgeon from May 2009 - October 2016. Patients were divided into two groups based on the technique used. Those in the first group had conventional split osteotomy using an osteotome and hammer for splitting (conventional group, 736 sides), and in those in the second group the manual twist technique was used (manual group, 802 sides). Patients who sustained Sunderland fifth degree injuries were identified from an existing record of nerve repairs. Fisher's exact test was used to evaluate the significance of the number of injuries to the nerve in each group. Conventional osteotomy and hammer-assisted SSRO resulted in 8/736 (1.1%) injuries to the IAN, whereas the manual twist splitting technique resulted in 1/802 injuries (0.1%). Our results confirm that the manual twist splitting technique significantly reduces the incidence of injury to the IAN, though the overall incidence was low.