How to select the lowest instrumented vertebra in Lenke type 5 adolescent idiopathic scoliosis patients?

BACKGROUND CONTEXT The lowest instrumented vertebra (LIV) determination in Lenke type 5 Adolescent Idiopathic Scoliosis (AIS) requires a thorough understanding and prediction of the correction force on the LIV from coronal, sagittal, and axial plane. Although many LIV selection criteria have been reported, none of them comprehensively evaluated the multidimensional characteristics of the LIV till now. PURPOSE To develop and evaluate our LIV selection criteria in Lenke type 5 AIS patients using pedicle screw system via posterior approach. STUDY DESIGN A retrospective study. PATIENT SAMPLE All consecutive patients with Lenke 5 curves who were treated with one-stage selective lumbar fusion using complete pedicle screw system in our center from January 2006 to December 2017, with minimum 2-year follow-up. OUTCOME MEASURES Age, gender and Risser grade, fused levels, operating time, intraoperative blood loss, complications, and Scoliosis Research Society (SRS)-22 questionnaires outcome were recorded. Coronal, sagittal, and axial parameters were measured from plain radiographs. METHODS A total of 138 consecutive patients with Lenke 5 curves treated with selective lumbar fusion were retrospectively analyzed, with minimum 2-year follow-up. Our LIV selection criteria include: (1) the most cephalad vertebrae touched by central sacrum vertical line (CSVL); (2) Nash-Moe rotation being equal or less than grade I on the standing AP radiograph; (3) CSVL cross between the two pedicles of LIV on concave bending film; (4) not at the apex of kyphosis. Radiographic data, operative data, perioperative complications and SRS-22 outcomes were collected and analyzed. RESULTS The mean follow-up period was 50.9±24.7 months. The thoracolumbar/lumbar curve was corrected from 46.9°±8.9° before surgery to 5.5°±2.6° at the final follow-up. The C7-CSVL was 19.7±6.2 mm before surgery and 5.2±3.4 mm at the final follow-up. The LIV translation was corrected from 22.3 ±5.4 mm before surgery to 4.8 ± 2.6 mm at the final follow-up, with the correction rate of 78.4%. The LIV tilt was corrected from 21.6 ± 4.4° before surgery to 2.6 ± 2.3° at the final follow up, with the correction rate of 87.9%. Our LIV saved 0.3 level than SRS-last barely touching vertebra, 0.6 level than SRS-last substantially touching vertebra, 0.9 level than neutral vertebra, and 1.4 level than stable vertebra. CONCLUSION The present study indicates using our LIV criteria, our study achieved the correction rate of thoracolumbar/lumbar curve as 88.9%, with the rate of adding on or coronal imbalance as 8.7% (12/138). The criteria may provide important guidance for preoperative decision-making in Lenke 5 AIS patients, and more multicenter prospective studies with larger samples are needed to further validate the findings of this study.