Radiographic Variability of Pelvic Incidence Following Surgical Correction of Thoracic and Thoracolumbar Scheuermann...

Study DesignRetrospective study.ObjectivesPelvic incidence (PI) is traditionally considered a fixed anatomical parameter; however, postoperative variability has been reported in adult deformity cohorts. Data regarding PI behavior in adolescent Scheuermann's kyphosis (SK), particularly according to deformity subtype and distal fusion level, remain limited. This study aimed to evaluate PI variability in thoracic (TSK) and thoracolumbar (TLSK) SK and to analyze its relationship with spinopelvic parameters.Methods102 consecutive SK patients who underwent single-stage posterior pedicle screw fusion(2015-2021) were retrospectively reviewed; 52 met inclusion criteria (TSK n=30,TLSK n=22). Thirty age-matched healthy controls were included. Radiographic parameters (TK,TLK,GK,LL,CL,PI,PT,SS,SVA,PI-LL mismatch) were measured on standardized standing whole-spine radiographs. Reliability was assessed using ICC and smallest detectable change(SDC95). Intergroup comparisons, correlation, and exploratory multivariate regression analyses were performed.ResultsReliability for PI, PT, and SS was excellent(ICC 0.92-0.97). Preoperatively, TLSK demonstrated lower PI and SS than TSK(p<0.05). At final follow-up(mean 4.6±2.2 years), PI increased significantly in TLSK (ΔPI +6.18°), exceeding SDC95, whereas no significant change was observed in TSK. The intergroup ΔPI difference was 5.22°(p=0.050). Distal fusion(≥L3) was associated with greater ΔPI. ΔPI correlated positively with postoperative PT and SS and negatively with LL. In multivariate analysis, postoperative PT(positive) and LL(negative) remained independently associated with ΔPI (R²=0.345, p=0.001).ConclusionsTLSK patients exhibit lower baseline PI and modest postoperative PI increase compared with TSK. Postoperative PI variability appears related to pelvic posture and lumbar alignment rather than definitive anatomical remodeling. These findings highlight the importance of comprehensive spinopelvic assessment during surgical planning and follow-up of Scheuermann kyphosis.