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Purpose: In Lenke type 5 and 6 curves, a major thoracolumbar or lumbar curve, the rates of PJK are reported as high as 50%. The purpose of this study was to confirm the rate of PJK, investigate possible risk factors, and evaluate surgical complications and the long-term effects of PJK on patient outcomes., Methods: A retrospective review of multicenter data identified 192 with patients with 2 year and 94 with 5-year follow-up. Included patients had a Lenke type 5 or 6 curve and underwent a selective thoracolumbar or lumbar curve fusion. All radiographs preoperatively and postoperatively (1 year, 2 years, and 5 years) were evaluated. Demographic and radiographic data was analyzed as risk factors for PJK using a multi-variate regression. Outcomes scores and complications were compared between groups., Results: 17 patients (8.9%) developed radiographic PJK; 1 at 1 year, 7 at 2 years, and another 9 at 5 years. All 17 patients had an upper instrumented vertebra (UIV) within 3 levels or less caudal of the thoracic kyphosis apex (the most horizontal vertebra on the sagittal); no patient with a UIV 4 or more levels from the thoracic apex (n = 96) developed PJK (X 2  = 13.03, p < 0.001). In addition, PJA > 8° was found to significantly increase the risk of PJK (p = 0.039). SRS scores were significantly worse for PJK patients at 5 years in the self-image and function (p < 0.01)., Conclusion: In Lenke 5/6 curves, no patient with a UIV 4 or more levels caudal to the thoracic kyphosis apex had PJK up to 5 years postoperatively. PJA greater than 8° was identified as a risk factor for PJK. Patients with radiographic PJK had worse SRS scores 5 years postoperatively., (© 2023. The Author(s), under exclusive licence to Scoliosis Research Society.)