Distal adding-on phenomenon after selective fusion for idiopathic thoracic scoliosis

English Keywords:Idiopathic scoliosis  Selective fusion  Main thoracic curve  Adding-on

English Abstract:

  【Abstract】 Objectives: To investigate the prevalence of distal adding-on phenomenon after selective fusion in adolescent idiopathic scoliosis(AIS) patients having a main thoracic curve, and to determine its risk factors.Methods: This study retrospectively recruited 110 AIS patients having a main thoracic curve(Lenke type 1A), who underwent one-stage anterior or posterior selective fusion surgery. There were 20 boys and 90 girls, with a mean age of(14.2±2.0) year and a mean thoracic curve of 48.2°±7.8°. All the patients took the standing long-cassette anteroposterior radiographs of spine before surgery, immediately after surgery and at postoperative follow-up. The gender, chronologic age, Risser sign, operative approach, position of stable vertebra(SV) and lowest instrumented vertebra(LIV) and fusion levels were recorded. Cobb angles were measured at initial visit and every time of follow-up after surgery. Then the incidence of distal adding-on phenomenon was calculated, and the risk factors were analyzed. Results: The thoracic curve of the cohort averaged 16.7°±6.1° immediately after surgery and 22.0°±8.5° at final follow-up, respectively. The mean follow-up was 21±5 months. At final follow-up, distal adding-on was observed in 19 patients(17.3%). Compared with the patients without distal adding-on, those with distal adding-on had lower Risser grade (2.1±1.4 versus 3.1±1.3, P=0.002), fewer months since menarche (11.2±14.2 months versus 21.9±18.9 months, P=0.002), more flexible in the compensatory lumbar hemicurve[(97.0±9.1)% versus (90.5±15.5)%, P=0.017], and higher LIV position relative to SV(1.5 vertebrae versus 0.7 vertebra, P=0.003). The incidence of distal adding-on was higher in patients who had lower Risser grade, open triradiate cartilages, or more flexible lumbar hemicurve, or who were at pre-menarche or less than 1 year since menarche, or who were treated with higher location of LIV in relation to SV. According to the results of Logistic regression, LIV-SV≤-2, open triradiate cartilage and more flexible lumbar hemicurve were the independent risk factors contributing to distal adding-on. Conclusions: Selective fusion for thoracic scoliosis has a risk of distal adding-on phenomenon, in which the selection of LIV together with the maturity of growth and the flexibility of the lumbar hemicurve are involved.