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Retrospective study.The objective was to investigate the effect of apical pedicle screw placement on surgical outcomes of Lenke 1 adolescent idiopathic scoliosis (AIS).Pedicle screw instrumentation achieves satisfactory correction of scoliosis in thoracic AIS patients, but the effect of apical screw placement is unclear.Lenke 1 AIS patients with all pedicle screw instrumentation between January 2009 and January 2011 were reviewed. According to the presence of apical vertebra instrumentation, 38 patients (group A) were identified without apical screw placement. 25 patients (group B) instrumented with both concave, and convex apical screws and 50 patients (group C) with either concave or convex apical pedicle screw instrumentation were also enrolled according to matched age and Cobb angles. Cobb angle correction, apical vertebral derotation, misplacement of apical screws, functional outcomes, and patient satisfaction were evaluated.Demographic parameters and preoperative Cobb angle, curve flexibility, and apex rotation were similar among the 3 groups (P>0.05). Postoperatively, there was no significant difference regarding the number of fused vertebrae, Cobb angle correction rate, or loss of correction. However, the degree of apical vertebral derotation was significantly lower in group A (17.8%) than in groups B (49.1%) and C (34.3%) (P<0.001). In group B, 6 screws inserted on the concavity and 5 on the convexity of the apex were identified as malpositioned; whereas in group C, 3 on the concavity and 2 on the convexity were malpositioned screws. Self-image and satisfaction were highest for patients in group B.For patients with moderate Lenke 1 AIS (Cobb angle, 50–70 degrees), the insertion of apical pedicle screws did not significantly improve curve correction, but it had a marked positive effect on the derotation of apical vertebrae, subsidence of the rib hump, and patient satisfaction.