Lowest instrumented vertebrae selection in posterior fusion of Lenke 3C/6C adolescent idiopathic scoliosis: L3 versus L4, when LEV is L4.

Abstract

In structural thoracolumbar/lumbar (TL/L) curves, lowest instrumented vertebra is selected mostly as the lower end vertebra (LEV). To save more lumbar mobile segments, fusion may be stopped one level proximal. This study aimed to compare the radiologic and functional outcomes of Lenke type 3C and 6C adolescent idiopathic scoliosis patients according to distal fusion level. 109 patients with Lenke 3C and 6C AIS, which had L4 as LEV and underwent posterior fusion were retrospectively evaluated. Lowest instrumented vertebra (LIV) was selected intraoperatively either as L3 or L4 depending on the disc alignment below LIV. In 49 patiens LIV was L3, while 60 patients were fused to L4. Two groups were compared according to radiologic and clinical outcomes preoperatively and two years postoperatively. Operation times were recorded. Preoperative values of both groups were similar. Regarding postoperative radiographic values, only LIV disc angle was different between groups, which was significantly higher in L3 group at two years follow-up. Coronal or sagittal imbalance was not observed. Surgical times and postoperative clinical outcomes were also similar. In TL/L curves which have L4 as LEV, satisfactory results can be achieved with stopping the fusion at L3, if a proper disc alignment below LIV can be obtained intraoperatively. Higher amount of LIV disc angle in L3 group did not cause coronal and sagittal imbalance. Although clinical outcomes are similar with stopping at L3 or L4, fusion to L3 may be prefered to save one more mobile disc.