Does baseline thoracolumbar shape influence patterns of cervical decompensation following surgical adult spinal deformity correction?

Abstract

Adult spinal deformity (ASD) surgery is complex and may lead to postoperative cervical deformity (CD) and/or proximal junctional kyphosis. The Roussouly classification describes four types of baseline thoracolumbar (TL) morphology, which differentially influence surgical outcomes. However, their role in predicting CD remains underexplored. This study aimed to stratify TL-ASD patients by Roussouly types and examine postoperative CD development patterns. The authors included operative ASD patients with no prior fusion and complete radiographic data at baseline, 6 weeks, 1 year, and 2 years. Patients were categorized into Roussouly types 1-4 using baseline pelvic incidence and lumbar lordosis apex. CD was assessed using a point system: cervical sagittal vertical axis (cSVA) of 40-80 mm = 1 point, T1 slope minus cervical lordosis (TSCL) of 15°-20° = 1 point, cSVA > 80 mm = 2 points, and TSCL > 20° = 2 points. CD was defined as a score ≥ 2. Statistical comparisons and multivariate logistic regression were used to assess CD risk across Roussouly types. A total of 546 patients (77% female, mean age 60.9 ± 14.3 years, mean BMI 27.3 ± 5.7 kg/m2, mean Charlson Comorbidity Index score 1.7 ± 1.7) were included. The mean number of fused posterior levels was 10.6 ± 4.5, with a mean estimated blood loss of 1548 ± 1450 mL, mean operative time of 438 ± 180 minutes, and mean length of stay of 7.7 ± 4.2 days. At baseline, 239 (43.8%) patients met CD criteria. The Roussouly distribution was as follows: type 1 (8.4%), type 2 (12.6%), type 3 (47.3%), and type 4 (31.7%). Among 307 patients without baseline CD, 174 (31.9%) developed CD within 2 years: 99 (32.2%) at 6 weeks, 44 (14.3%) at 1 year, and 31 (10.1%) at 2 years. Type 2 patients had higher odds of developing CD at 2 years compared to type 3 patients (OR 2.15, p = 0.019). Type 4 patients had lower odds of developing CD (OR 0.22, p = 0.12). Roussouly type influences the timing and likelihood of CD following ASD correction. Type 1 patients tended to develop CD earlier, while type 2 patients showed delayed onset. Type 4 morphology may be protective against CD.