Disc Wedge and Vertebral Body Tilt Angle Below Lower Instrumented Vertebra After Posterior Correction and Fusion in Patients With a Structural Thoracolumbar/Lumbar Curve

Study Design. A retrospective cohort study. Objective. The purpose of this study was to evaluate the stability of remained lumbar curve by the review of serial changes in 13/14 disc wedge and L4 body tilt angle in patients with idiopathic scoliosis who underwent posterior-only fusion to L3 lower instrumented vertebra (LIV) for the correction of structural thoracolumbar/lumbar (TL/L) curve for a minimum 5-year follow-up. Summary of Background Data. There has been some debate in the selection of L3 or L4 as the LIV for the correction of structural TL/L curve. However, there is a limited information about the changes in disc wedge or vertebral body tilt angles below the L3 LIV. Methods. Forty-seven patients were included (mean age 16 yr 7 mo, follow-up 8 yr 2 mo). The Cobb angle of the TL/L curve, L3/L4 disc wedge angle, L4 tilt angle, trunk shift (TS), and apical vertebral translation (AVT) were compared preoperatively and at postoperative 5 days, 1 month, 6 months, 2 years, and final follow-up. Results. At postoperative 5 days, Cobb angle of the TL/L curve, L4 tilt angle, and AVT were improved, except TS and 13/14 disc wedge angle. The L3/L4 disc wedge and L4 tilt angle were most increased at postoperative 6 months and decreased thereafter. L4 tilt angle, AVT, and TS were improved during postoperative follow-up, except L3/L4 disc wedge angle. Finally, Cobb angle of the TUL curve (11.8 degrees +/- 5.1 degrees, P<0.001), L4 tilt angle (7.6 degrees +/- 4.0 degrees, P< 0.001), AVT (19.2 +/- 9.3 mm, P< 0.001), and TS (-5.0 +/- 10.0 mm, P= 0.041) were improved; however, L3/L4 disc wedge angle (3.3 degrees +/- 2.3 degrees , P=0.442) was not improved compared to the preoperative evaluation. Conclusion. When LIV was selected as the L3, the correction of TL/L curve was maintained in a minimum 5-year follow-up with the improvement of L4 tilt angle, AVT, and TS; however, L3/L4 disc wedge angle may remain.