title: Bad splits in bilateral sagittal split osteotomy: systematic review and meta-analysis of reported risk factors.
abstract: An unfavourable and unanticipated pattern of the bilateral sagittal split osteotomy (BSSO) is generally referred to as a 'bad split'. Patient factors predictive of a bad split reported in the literature are controversial. Suggested risk factors are reviewed in this article. A systematic review was undertaken, yielding a total of 30 studies published between 1971 and 2015 reporting the incidence of bad split and patient age, and/or surgical technique employed, and/or the presence of third molars. These included 22 retrospective cohort studies, six prospective cohort studies, one matched-pair analysis, and one case series. Spearman's rank correlation showed a statistically significant but weak correlation between increasing average age and increasing occurrence of bad splits in 18 studies (ρ=0.229; P<0.01). No comparative studies were found that assessed the incidence of bad split among the different splitting techniques. A meta-analysis pooling the effect sizes of seven cohort studies showed no significant difference in the incidence of bad split between cohorts of patients with third molars present and concomitantly removed during surgery, and patients in whom third molars were removed at least 6 months preoperatively (odds ratio 1.16, 95% confidence interval 0.73-1.85, Z=0.64, P=0.52). In summary, there is no robust evidence to date to show that any risk factor influences the incidence of bad split.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Academic Medical Centre (AMC), Amsterdam, The Netherlands. Electronic address: s.a.steenen@amc.uva.nl.
authors.forename: S A
authors.initials: SA
authors.lastname: Steenen
authors.affiliation: Department of Social Dentistry and Behavioural Sciences, Academic Centre for Dentistry (ACTA) in Amsterdam, University of Amsterdam and VU University, Amsterdam, The Netherlands.
authors.forename: A J
authors.initials: AJ
authors.lastname: van Wijk
authors.affiliation: Department of Oral and Maxillofacial Surgery, Spaarne Gasthuis Haarlem, Academic Medical Centre (AMC), Amsterdam, and Academic Centre for Dentistry (ACTA) in Amsterdam, The Netherlands.
authors.forename: A G
authors.initials: AG
authors.lastname: Becking
mesh_terms: D000367:Age Factors; D006801:Humans; D007431:Intraoperative Complications / Q000453:epidemiology*; D008334:Mandible; D008964:Molar, Third / Q000601:surgery; D059229:Osteotomy, Sagittal Split Ramus / Q000009:adverse effects* / Q000379:methods / Q000706:statistics & numerical data*; D011446:Prospective Studies; D012189:Retrospective Studies; D012307:Risk Factors
keywords: age; bad split; bilateral sagittal split osteotomy; intraoperative complications; mandibular fracture; orthognathic surgery; risk factors; sagittal ramus osteotomy; surgical technique; third molar