Determinants of early skeletal relapse after SSRO advancement in high-angle patients with mandibular retrognathia: A retrospective study

Background: Skeletal relapse after mandibular advancement via sagittal split ramus osteotomy (SSRO) remains a major concern in mandibular retrognathia. While advancement magnitude is frequently implicated, the independent contributions of Frankfort mandibular angle (FMA) and concomitant genioplasty remain debated. Methods: This retrospective study included 37 consecutive patients with mandibular retrognathia who underwent SSRO with or without genioplasty (January 2020–December 2024). Lateral cephalograms were obtained preoperatively and at 1 week and 6 months postoperatively. Using the Frankfort horizontal plane and a vertical reference plane through Sella, horizontal and vertical positional changes of B-point, Pogonion, and Menton were measured. Surgical movement was defined as the preoperative to 1-week change; relapse as the 1-week to 6-month change. Multivariate linear regression models included movement magnitude, genioplasty, and preoperative FMA. Exploratory models tested movement × FMA and movement × genioplasty interactions. Results: The cohort was predominantly female (36/37) with a mean age of 28.6 ± 6.4 years and a high mean FMA of 37.0 ± 2.8° Advancement magnitude was the only significant predictor of relapse, at B-point (horizontal and vertical) as well as at Pogonion and Menton (horizontal) (all p < 0.05). Neither FMA nor genioplasty showed independent effects. Interaction terms were not significant; however, visualization suggested a steeper relapse-advancement slope at higher FMA (40° vs 30°). Conclusions: In early follow-up, mandibular advancement magnitude was the primary determinant of skeletal relapse after SSRO for mandibular retrognathia, whereas FMA and genioplasty were not significant independent predictors. However, exploratory visualization suggested a possible advancement–FMA interaction, warranting larger studies to clarify potential effect modification by skeletal pattern.