Identifying Distinct Risk Factors for Early-Onset and Late-Onset PJK in ASD: A Comparative Analysis Across Non-PJK, Early-Onset PJK, and Late-Onset PJK Groups

Study DesignRetrospective cohort study.ObjectivesThe risk factors for proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) are well established, but their association with onset timing remains unclear. This study aims to identify distinct risk factors for early-onset and late-onset PJK.MethodsThis study included 96 ASD patients who underwent corrective surgery (fusion ≥5 levels, UIV: T1-L1, LIV: L5/S1) with ≥2 years of follow-up. Patients were categorized into Non-PJK, Early-Onset PJK (≤6 months), and Late-Onset PJK (>6 months) groups. Clinical characteristics were compared to identify potential risk factors (<i>P</i> < .10). Multinomial logistic regression was used to evaluate the independent effects of these variables on early-onset and late-onset PJK.ResultsAmong 96 patients, 44 (45.8%) developed PJK (31 early-onset, 13 late-onset), and 7 (7.3%) developed PJF, including 6 cases in the Early-Onset group (19.4%, <i>P</i> = .005). After initial screening and addressing multicollinearity, preoperative PI, UIV location, and postoperative PI-LL and L1PA were finally included in regression analysis. Lower thoracic UIV (T7-L1) increased the risk of Early-Onset PJK (OR = 5.27, <i>P</i> = .015). Higher preoperative PI was associated with Late-Onset PJK, with a 9% increased risk per degree (OR = 1.09, <i>P</i> = .027).ConclusionsMost PJK cases occur within 6 months and have a higher risk of PJF. Lower thoracic UIV increases Early-Onset PJK risk, while higher preoperative PI predisposes to Late-Onset PJK. Strategies should focus on preventing Early-Onset PJK in lower thoracic UIV cases and long-term monitoring for Late-Onset PJK in high-PI patients.