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Purpose: To compare the results of two different instruments made of stainless steel and titanium alloy for correction of single thoracic adolescent idiopathic scoliosis (AIS) using pedicle screw instrumentation. Materials and Methods: A total of 141 patients with single thoracic AIS treated with pedicle screw instrumentation and selective thoracic fusion were retrospectively reviewed after a follow-up of 2 years. The patients had a main thoracic curve of 40° to 75° and were divided into two groups based on instrument materials; S group (stainless steel, n=90) and T group (titanium alloy, n=51). The diameter of the stainless steel rod used was 7.0 mm while that of the titanium alloy rod was 6.35 mm or 6.0 mm. Standing long-cassette radiographic measurements including various coronal and sagittal parameters for the preoperative, early postoperative and 2-year postoperative followup were analyzed. There were no significant differences in the preoperative curve characteristics between the two groups. Results: In the S group, the preoperative main thoracic curve of 51.3°±8.4° was improved to 19.0°±7.6° (63.1% correction) and the lumbar curve of 32.3°±8.4° spontaneously decreased to 12.7°±8.2° (62.9% correction) at 2 years postoperatively. In the T group, the preoperative main thoracic curve of 49.5°±8.4° and the lumbar curve of 30.3°±8.9° was improved to 18.8°±7.4° (62.2% correction) and 11.3°±5.4° (63.3% correction), respectively. The corrections of coronal curves were not statistically different between the two groups (p>0.05). The thoracic kyphosis was changed from 16.8°±8.5° to 24.3°±6.1° in the S group and from 19.6°±11.2° to 26.6°±8.5° in the T group. There were no significant differences in the changes of sagittal curves, coronal and sagittal balances at the 2-year follow-up and the number of fused segments and used screws between the two groups (p>0.05). Conclusion: When conducting surgery for single thoracic AIS using pedicles screw instrumentation, two different instruments made of stainless steel and titanium alloy showed similar corrections for coronal and sagittal curves. [ABSTRACT FROM AUTHOR]