The impact of Roussouly sagittal profile changes on postoperative outcomes.

Objective: The aim of this retrospective study was to investigate the relationship between postoperative Roussouly sagittal profile changes and patient outcomes.

Methods: From a prospectively collected, single-center database, the authors reviewed the records of patients with adult spinal deformity (ASD) who had clinical and radiographic data from baseline to 2 years after surgery. The patients were stratified by their Roussouly curve type (current sacral slope-based and "theoretical" pelvic incidence-based types). Means comparison tests (ANOVA and chi-square) were used to assess differences among Roussouly groups. Backstep logistic regression analyses were used to analyze associations between Roussouly sagittal profile changes and patient outcomes, including minimum clinically important differences (MCIDs) in functional metrics.

Results: Five hundred twenty-five patients, 79% of whom were female, were included in this study. The mean age of the cohort was 60.8 ± 14.1 years, BMI was 27.2 ± 5.5 kg/m2, and Charlson Comorbidity Index score was 1.72 ± 1.68. According to the Roussouly classification, 8.3% of patients had a Roussouly type 1 (R1) curve, 53.6% type 2 (R2), 26.3% type 3 (R3), and 11.9% type 4 (R4). Overall, 39% of patients had a changed Roussouly shape postoperatively: 59% had R1, 58.5% R2, 48.1% R3, and 26.7% R4 (p < 0.001). Forty-eight percent of patients matched the theoretical Roussouly type postoperatively (41% R1, 41.5% R2, 51.9% R3, and 73.3% R4, p < 0.001). When controlling for baseline clinical and radiographic differences, the Roussouly type changes associated with a higher risk of proximal junctional kyphosis or proximal junctional failure were as follows: R1 to R2 (OR 2.5, 95% CI 1.1-5.6, p = 0.024), R2 to R4 (OR 2.8, 95% CI 1.1-7.7, p = 0.039), and R3 to R4 (OR 2.3, 95% CI 1.1-4.9, p = 0.033). R4 to R3 switches had the highest mechanical complication risks (OR 3.4, 95% CI 1.2-9.4, p = 0.016). R1 to R2 changes had the highest rate of attaining an MCID in the Oswestry Disability Index at 6 weeks (23.5%, p = 0.004). Roussouly type changes were not associated with differences in the MCID on the refined 22-item Scoliosis Research Society patient outcome questionnaire (SRS-22r) up to 2 years after surgery.

Conclusions: While a significant portion of patients matched their postoperative theoretical Roussouly type, many of those matched at baseline were prone to become unmatched postoperatively. Postoperative Roussouly shape changes influence patient outcomes and should be accounted for when planning ASD surgery.