P106. Normalization of pelvic tilt following corrective adult spinal deformity surgery: Analysis of prevalence, timing, and factors determining occurrence

Abstract

<h3>BACKGROUND CONTEXT</h3> Increasing pelvic tilt (PT) is a primary compensatory mechanism in adult spinal deformity (ASD). By SRS-Schwab criteria, PT >20° is considered pathologic. Some ASD patients improve their PT following ASD correction, while others do not. The driving forces behind this lack of PT-response are not well defined. <h3>PURPOSE</h3> To determine the perioperative characteristics associated with PT normalization after ASD corrective surgery. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>PATIENT SAMPLE</h3> A total of 176 ASD patients. <h3>OUTCOME MEASURES</h3> Patient profile, radiographic parameters, and surgical factors associated with PT normalization. <h3>METHODS</h3> Operative ASD patients fused to S1/pelvis with full preoperative data as well as preoperative (BL), 6-week (6W), 1-year (1Y), and 2-year (2Y) postop PT measurements were included. PT normalization was assessed at 6W and 2-year follow-up. Univariate analyses were used to compare normalized (PTNorm) and non-normalized (NON) patients in terms of demographics, surgical and radiographic descriptors, postoperative alignment, and clinical outcomes. Multivariate regression and ROC curve assessed periop factors predicting 6W PT normalization. Conditional inference tree (CIT) determined thresholds for the continuous variables identified as independent predictors of PT normalization. <h3>RESULTS</h3> There were 176 ASD patients that met inclusion criteria (62.9±10.2years, 80%F, BMI 26.9±4.9 kg/m2, CCI: 1.88), and underwent surgery (levels fused 12.1±3.9, EBL: 1955mL, op time: 402min). At each time point, mean PT was as follows: BL: 25.7º, 6-week: 19.0º, 1-year: 21.2º, and 2-year: 22.3°. Patients classified as having normal PT by SRS-Schwab criteria (PT<20º): BL: 27.8%(n=49), 6W: 52.3%, 1-year: 47.2%, 2-year: 40.9%. Of the 127 patients with non-normal PT at BL, 50 (39.4%) normalized postoperatively by 6 weeks. Few patients normalized in PT after the 6-week mark: 7 by 1-year and another 2 by 2-year postop for a total of 37 2-year PTNorm patients. Sixteen patients with non-normal PT at BL normalized by 6W, but reverted at 2-year. Both 6 weeks and 2 years PTNorm patients had higher levels fused than NON patients (both p<0.05). 6W PTNorm patients were more likely to undergo combined approach(p=0.005). Two-year PTNorm patients were more likely to have undergone VCR(p=0.011). Normalized and non-normalized patients did not differ in BL SRS-Schwab PI-LL and SVA or in GAP proportionality (all p>0.05). Six weeks PTNorm patients were more likely to be overcorrected in PT, PI-LL, and SVA compared to NON patients at 6 weeks postop (all p<0.05). The same held true for 2-year PTNorm patients and 2-year radiographic alignment. Compared to non-normalized patients, both 6 weeks PTNorm patients and 2-year PTNorm patients had lower rates of implant failure and rod fracture (all p<0.05). 6W PTNorm patients had a lower revision rate(p=0.018). Binary logistic regression with CIT identified independent predictors of PT normalization by 6 weeks: undergoing combined approach, UIV at or above T8, levels fused >10, invasiveness score >109, baseline cSVA<41.5°, 6 weeks PI-LL diff ≥21.0°, 6 weeks sacral slope diff ≥7.9°, 6 weeks PT diff ≥7.5°; all p<0.05. Validation of a predictive model for 6 weeks normalized vs non-normalized patients including these factors yielded an AUC of 85.2%. <h3>CONCLUSIONS</h3> PT normalization following ASD correction occurred in almost 40% of patients by 6 weeks postop. Normalization is more likely to occur in patients where reconstruction addresses lumbopelvic mismatch, extends above the apex of the thoracic kyphosis, and has adequate surgical invasiveness to achieve full alignment correction. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.