(27) Neurosensory Defects After Sagital Split Osteotomy: A Scoping Review

Abstract: A known and expected outcome of the sagittal split osteotomy (SSO) is a high incidence of inferior alveolar nerve (IAN) injuries and subsequent neurosensory defects (NSD). The reported incidence of IAN injury after SSO varies greatly with many studies quoting incidences ranging from 0%-100%.[1] The relative risk and incidence of NSD after SSO is highly dependent on confounding variables.[2] Many of these confounders represent modifiable variables (i.e. surgeon experience, method of fixation, intraoperative IAN manipulation) while others are non-modifiable (age, gender, magnitude of movement). The literature is chock-full of studies on IAN injury after SSO. However, there has yet to be a study summarizing the available body of literature, assessing its validity and evaluating its merit. Here we conducted a scoping review to assess and critique the available literature for studies examining the incidence of NSD at least one year after SSO.
We preformed searches using Google Scholar, the National Center for Biotechnology Information, and PubMed databases using various medical subject heading (MeSH) terms for articles examining the incidence of NSD in the distribution of the IAN after SSO. Articles included were those published after 1999, in English, involving only the SSO on humans in vivo, without concomitant genioplasty and with at least one year follow up. The returned articles were filtered by the authors at the title, abstract and full text levels. The remaining articles were examined to for the presence of result stratification by confounding variables associated with statistically significant incidence of NSD. Descriptive statistics were employed.
The original search returned 1,435 studies, after the screenings, 49 articles were included in the review. The final articles included 11,031 total nerves. Forty-three articles were prospective (cohort, RCT, ect.) and the other 6 retrospective analyses. The reported incidence of NSD at one year after SSO varies greatly among studies – anywhere from 0% to 90%. The confounding variables most frequently associated with statically significant increase in NSD were age (12), intraoperative nerve manipulation (8), magnitude of movement (6), gender (5), type of movement (5), method of fixation (4), presence of impacted third molars (2), and surgical technique/surgeon experience (2). The incidence of NSD one year after SSO was 22.74 ± 6.48 (95% CI: 16.3 - 29.2).
A NSD in the distribution of the IAN is an expected outcome after SSO. We should tailor our expectations for NSD incidence after SSO based on the presence or absence of certain confounding variables.

References
1. G.K. Essick, C. Phillips, T.A. Turvey, M. Tucker. Facial altered sensation and sensory impairment after orthognathic surgery. Int J Oral Maxillofac Surg, 36 (2007), p. 577
2. J.O. Agbaje, A.S. Salem, I. Lambrichts, et al. Systematic review of the incidence of inferior alveolar nerve injury in bilateral sagittal split osteotomy and the assessment of neurosensory disturbances. Int J Oral Maxillofac Surg, 44 (2015), p. 447