Methods: Patients with Lenke 1 AIS undergoing posterior spinal fusion were included. Standing and fulcrum bending radiographs on the coronal and sagittal planes were analyzed at preoperative, immediate, and 2-year postoperative periods. The primary outcome was postoperative hypokyphosis (T5–12 thoracic kyphosis [TK] <20°). Risk factors for postoperative hypokyphosis were identified by multivariate logistic regression, and the optimal cutoff for significant risk factors was determined by receiver operating characteristic analysis. Results: In total, 156 patients were included in the analysis, of which 68 (43.6%) were hypokyphotic at 2-year follow-up. Low T5–12 TK on lateral view fulcrum bending films (immediate postoperative odds ratio [OR], 0.870; 95% confidence interval [CI], 0.826–0.917; 2-year postoperative OR, 0.916; 95% CI, 0.876–0.959; p<0.001) and high convex side implant density (2-year postoperative OR, 1.749; 95% CI, 1.056–2.897; p=0.03) were significant risk factors for postoperative hypokyphosis. Other baseline demographic and surgical factors did not affect postoperative kyphosis correction. The T5–12 TK cutoff on fulcrum bending for 2-year postoperative hypokyphosis was 12.45° (area under the curve, 0.773; 95% CI, 0.661–0.820). Conclusions Fulcrum bending radiography is useful in assessing coronal and sagittal flexibility for preoperative planning. In patients with T5–12 kyphosis <12.5° on lateral view fulcrum bending radiographs, Ponte osteotomies or releases, or a decrease in convex side implant density should be considered to improve kyphosis restoration and reduce the risk of 2-year postoperative hypokyphosis.

Methods: Patients with Lenke 1 AIS undergoing posterior spinal fusion were included. Standing and fulcrum bending radiographs on the coronal and sagittal planes were analyzed at preoperative, immediate, and 2-year postoperative periods. The primary outcome was postoperative hypokyphosis (T5–12 thoracic kyphosis [TK] <20°). Risk factors for postoperative hypokyphosis were identified by multivariate logistic regression, and the optimal cutoff for significant risk factors was determined by receiver operating characteristic analysis. Results: In total, 156 patients were included in the analysis, of which 68 (43.6%) were hypokyphotic at 2-year follow-up. Low T5–12 TK on lateral view fulcrum bending films (immediate postoperative odds ratio [OR], 0.870; 95% confidence interval [CI], 0.826–0.917; 2-year postoperative OR, 0.916; 95% CI, 0.876–0.959; p<0.001) and high convex side implant density (2-year postoperative OR, 1.749; 95% CI, 1.056–2.897; p=0.03) were significant risk factors for postoperative hypokyphosis. Other baseline demographic and surgical factors did not affect postoperative kyphosis correction. The T5–12 TK cutoff on fulcrum bending for 2-year postoperative hypokyphosis was 12.45° (area under the curve, 0.773; 95% CI, 0.661–0.820). Conclusions Fulcrum bending radiography is useful in assessing coronal and sagittal flexibility for preoperative planning. In patients with T5–12 kyphosis <12.5° on lateral view fulcrum bending radiographs, Ponte osteotomies or releases, or a decrease in convex side implant density should be considered to improve kyphosis restoration and reduce the risk of 2-year postoperative hypokyphosis.

Methods: Patients with Lenke 1 AIS undergoing posterior spinal fusion were included. Standing and fulcrum bending radiographs on the coronal and sagittal planes were analyzed at preoperative, immediate, and 2-year postoperative periods. The primary outcome was postoperative hypokyphosis (T5–12 thoracic kyphosis [TK] <20°). Risk factors for postoperative hypokyphosis were identified by multivariate logistic regression, and the optimal cutoff for significant risk factors was determined by receiver operating characteristic analysis. Results: In total, 156 patients were included in the analysis, of which 68 (43.6%) were hypokyphotic at 2-year follow-up. Low T5–12 TK on lateral view fulcrum bending films (immediate postoperative odds ratio [OR], 0.870; 95% confidence interval [CI], 0.826–0.917; 2-year postoperative OR, 0.916; 95% CI, 0.876–0.959; p<0.001) and high convex side implant density (2-year postoperative OR, 1.749; 95% CI, 1.056–2.897; p=0.03) were significant risk factors for postoperative hypokyphosis. Other baseline demographic and surgical factors did not affect postoperative kyphosis correction. The T5–12 TK cutoff on fulcrum bending for 2-year postoperative hypokyphosis was 12.45° (area under the curve, 0.773; 95% CI, 0.661–0.820). Conclusions Fulcrum bending radiography is useful in assessing coronal and sagittal flexibility for preoperative planning. In patients with T5–12 kyphosis <12.5° on lateral view fulcrum bending radiographs, Ponte osteotomies or releases, or a decrease in convex side implant density should be considered to improve kyphosis restoration and reduce the risk of 2-year postoperative hypokyphosis.