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目的:探讨Lenke C型青少年特发性脊柱侧凸（adolescent idiopathic scoliosis，AIS）下端固定椎（lowest instrumented vertebra，LIV）终止于腰弯顶椎（apical vertebra of lumbar curve，L-AV）患者发生远端叠加现象（adding-on，AO）的危险因素。方法:73例Lenke C型AIS患者接受后路脊柱融合手术治疗，选择L-AV作为LIV，且术后随访超过2年。根据远端AO发生与否将患者分为AO组和非AO组。影像学测量参数包括胸弯、腰弯Cobb角及侧弯柔韧性，胸弯、腰弯顶椎偏移，L-AV旋转及倾斜角度，冠状面平衡，正位及凹侧bending位X线片Harrington稳定区，凸侧bending位X线片L-AV去旋转及L-AV/AV+1椎间盘开合情况等，采用脊柱侧凸研究会-22问卷（Scoliosis Research Society-22，SRS-22）评估患者临床疗效。对两组患者的影像学参数及临床疗效进行统计学分析。结果:73例AIS患者中AO组23例，非AO组50例。与非AO组相比，AO组患者术前L-AV位置较高，胸弯柔韧性较小，冠状面失平衡并向腰弯凸侧偏移，正位及凹侧bending位X线片Harrington稳定区较小，L-AV/AV+1椎间盘开合情况好的患者较少。Logistic回归分析结果表明，胸弯柔韧性、冠状面平衡、凹侧bending位X线片Harrington稳定区及L-AV/AV+1椎间盘开合情况是发生远端AO与否的重要预测因素。即选择L-AV作为LIV的最佳参数是胸弯柔韧性>40.0%，冠状面平衡77.8%。末次随访时AO组患者的腰弯明显增大，侧凸矫正率降低。但两组患者的SRS-22评分差异无统计学意义。结论:Lenke C型AIS患者如具有良好的胸弯柔韧性、冠状面平衡、L-AV/AV+1椎间盘开合情况，且凹侧bending位X线片Harrington稳定区较大，则LIV可以止于L-AV。“,”Objective:To investigate the radiographic risk factors related to the occurrence of distal adding-on (AO) in posteriorly treated Lenke modifier C adolescent idiopathic scoliosis (AIS) patients with the apical vertebra of the lumbar curve (L-AV) selected as the lowest instrumented vertebra (LIV).Methods:Seventy-three Lenke modifier C AIS patients were analyzed with a minimum of 2-year follow-up after posterior spinal fusion surgery with L-AV selected as LIV. Patients were grouped according to the occurrence of distal AO. Radiographical parameters were measured as follows: Cobb angle, curve flexibility and AV translation of the thoracic curve and lumbar curve, L-AV rotation and tilt, coronal balance, Harrington stable zone on anteroposterior (AP) film and concave bending film, L-AV derotation and L-AV/AV+1 disc opening or closing on convex bending film, etc. The Scoliosis Research Society-22 (SRS-22) score was used to evaluate clinical outcomes. Radiographic and clinical parameters were statistically analyzed between the two groups.Results:There were 23 patients in AO group and 50 patients in non-AO group. Preoperatively, the AO group had proximal L-AV, lower flexibility of the thoracic curve, coronal imbalance shifted to the convex side of the lumbar curve, lower Harrington stable zone on AP film and concave bending film, and less L-AV/AV+1 disc opening on convex bending film compared to non-AO group. The logistic regression revealed that the flexibility of the thoracic curve, coronal balance, Harrington stable zone on concave bending film, and L-AV/AV+1 disc opening or closing on convex bending film were significant predictors of distal AO. Specifically, the flexibility of the thoracic curve >40.0%, coronal balance77.8% might be optimal thresholds for selecting L-AV as LIV. At the final follow-up, AO group had larger lumbar curves and lower correction rates. No difference was found in the SRS-22 between the two groups.Conclusion:For Lenke modifier C AIS patients, LIV might be considered to stop at L-AV if there were good flexibility of the thoracic curves, coronal balance, L-AV/AV+1 disc opening on convex bending film, and large Harrington stable zone on concave bending film.