Lowest instrumented vertebrae selection for selective posterior fusion of moderate thoracolumbar/lumbar idiopathic scoliosis: lower-end vertebra or lower-end vertebra+1?

PURPOSE: To determine fusion necessity to one level below lower-end vertebra (LEV+1) in selective posterior fusion of moderate thoracolumbar/lumbar (TL/L) idiopathic scoliosis.
METHODS: A total of 37 patients with moderate TL/L idiopathic scoliosis (Cobb angle of TL/L curve between 30° and 60°) were identified and three patients with TL/L curve Cobb angle more than 60° were excluded. And the follow-up period was at least 2 years. Lowest instrumented vertebra (LIV) was one level proximal to LEV in three patients, LEV in 22 patients and LEV+1 in 12 patients. The three patients with TL/L Cobb angle more than 60° were all fused to LEV+1. Clinical and various radiographic measurements were collected before surgery, post-surgery and during last follow-up, and analytical comparisons were made between LIV = LEV patients and LIV = LEV+1 patients.
RESULTS: No significant difference was observed regarding clinical and radiographic parameters between LEV group and LEV+1 group preoperatively except LIV disc angle and LIV translation. The correction rate of unfused thoracic curve and TL/L curve was 52.7 and 79.9 % in LEV group and 52.5 and 83.7 % in LEV+1 group at the last follow-up, indicating no significant difference (P = 0.976 and P = 0.415, respectively). Coronal balance and sagittal alignments were also comparable between the two groups. LIV translation was slightly less in LEV+1 group (P = 0.028) at the last follow-up on the basis that LEV+1 was less translated than LEV preoperatively.
CONCLUSIONS: Our analysis almost showed no benefit for fusing to LEV+1 in moderate TL/L idiopathic scoliosis patients undergoing posterior selective fusion with pedicle screws. For patients with TL/L Cobb angle more than 60°, the distal fusion level probably needs to be LEV+1.