Effect of high BMI and overcorrected lordosis distribution index on the risk of proximal junctional kyphosis after age-adjusted sagittal correction in adult spinal deformity.

Abstract

Proximal junctional kyphosis (PJK) continues to develop in up to 23.7% of patients despite optimal sagittal alignment in adult spinal deformity (ASD) surgery. In this study, the authors aimed to identify the risk factors for PJK development in patients with ASD who achieved optimal age-adjusted sagittal correction. Data from a prospectively collected ASD database at the authors' tertiary hospital were retrospectively analyzed. Patients with ASD who underwent fusion from the low thoracic spine (T9-12) to the pelvis with a minimum follow-up duration of 1 year were included. Among them, only patients who achieved optimal sagittal age-adjusted alignment, which was defined as sagittal age-adjusted score (SAAS) between -1 and +1, were analyzed. The lordosis distribution index (LDI) correction statuses were evaluated based on the normative pelvic incidence-adjusted LDI values. PJK was defined as a proximal junctional angle > 20°. Various clinical and radiographic risk factors were compared between the non-PJK and PJK groups. The final study cohort included 148 patients (mean age 67.2 years, 87.8% female, mean BMI 26.1 kg/m2, mean total levels fused 7.5). During the mean follow-up duration of 39.5 months, PJK occurred in 42 patients (28.4%). Multivariate logistic regression analysis showed that high BMI and overcorrected LDI were significant risk factors for PJK development (OR 1.171 [95% CI 1.053-1.302], p = 0.004 for BMI; OR 3.576 [95% CI 1.218-10.504], p = 0.020 for LDI overcorrection). The PJK incidence was significantly higher in the LDI overcorrection group than in the non-LDI overcorrection group (41.4% vs 20.0%, p = 0.005). Despite optimal age-adjusted sagittal correction, PJK developed in a considerable proportion (28.4%) of patients. The associated factors for PJK in this patient group were a high BMI and overcorrected LDI. PJK could be further mitigated by properly managing these risk factors along with optimal sagittal correction.