Characteristics and risk factors for proximal junctional kyphosis in adult spinal deformity after correction surgery: a systematic review and meta-analysis

There are still controversies on characteristics and risk factors for proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) patients. The objective of this study is to explore the characteristics and risk factors for PJK in ASD. A systematic online search in databases including PubMed, EMBASE, Web of Science, and the Cochrane Library was performed to identify eligible studies. OR and weight mean difference with 95% CI were used to evaluate characteristics and risk factors. A total of 31 studies were finally included. ASD patients with PJK had larger proximal junctional angle (PJA), thoracic kyphosis (TK), pelvic incidence minus lumbar lordosis (PI-LL), and sagittal alignment. Age, female gender, and low BMD/osteoporosis were demographic risk factors for PJK. Using hooks at upper instrumented vertebra (UIV) and the selection of UIV above T8 could reduce the occurrence of PJK, while pelvic fixation was significantly associated with increased occurrence of PJK. Preoperative LL, preoperative pelvic tilt (PT), preoperative LL-TK, preoperative PI-LL, preoperative sagittal vertical axis (SVA), preoperative global spine alignment (GSA), postoperative PJA, change in PJA, postoperative TK, change in LL, change in SVA, and postoperative GSA were identified as risk factors for PJK. In conclusion, PJK patients had larger PJA, larger TK, smaller PI-LL, and larger sagittal alignment. Older female ASD patients with low BMD/osteoporosis are more likely to suffer from PJK. We recommend the following: (1) using hooks at UIV; (2) UIV should be chosen above T8, and pelvic fixation should be avoided if possible; (3) ideal correction of sagittal alignment should be performed to prevent the occurrence of PJK.