Sagittal Profiles and Their Reciprocal Changes Manifesting in Proximal Junctional Kyphosis Following Deformity Correction in Adolescent Idiopathic Scoliosis

Study Design Retrospective cohort study. Objectives To investigate sagittal profiles including sagittal shape and alignment in relation to proximal junctional kyphosis (PJK) following deformity correction in patients with adolescent idiopathic scoliosis (AIS). Methods A total of 282 AIS patients who underwent deformity correction were categorized into 2 groups according to the presence of PJK at the 2-year follow-up: the PJK group (n = 48) and the non-PJK group (n = 234). Sagittal shape was classified as normal thoracic kyphosis (TK), hypo-TK with/without thoracolumbar kyphosis (TLK), and cervico-thoracic kyphosis. Changes in Roussouly classification and correction relative to the functional T10 pelvic angle target were assessed to evaluate sagittal restoration and its association with PJK. Results The upper instrumented vertebra (UIV) level differed significantly between the 2 groups ( P = 0.002). The mean absolute Δ sagittal vertical axis (SVA) was also greater in the PJK group ( P = 0.008). Regarding sagittal shape, the PJK group was most prevalent in normal TK (43.8%) and cervico-thoracic kyphosis (31.3%), whereas the non-PJK group was most prevalent in hypo-TK without TLK (40.2%) ( P < 0.001). Multivariate logistic regression showed that lower UIV level, cervico-thoracic kyphosis, and greater ΔSVA were significantly associated with PJK. Conclusions UIV level, cervicothoracic kyphotic profile, and greater changes in the SVA were the contributing factors of development of radiographic PJK. In contrast to adult spinal deformity, PJK in AIS rarely causes serious clinical sequelae but instead represents reciprocal changes driven by the original sagittal shape and subsequent alterations in sagittal alignment.