Curve flexibility and maintenance of curve correction in alternate level pedicle screw fixation in adolescent idiopathic thoracic scoliosis

Abstract

INTRODUCTION: Flexibility is an important factor in preoperative planning for adolescent idiopathic scoliosis (AIS). It’s unknown if preoperative flexibility affects maintenance of correction in alternative level screw strategy (ALSS) until biologic stability. METHODS: A prospective study of 49 thoracic AIS-ALSS patients (mean age: 14.5-years; 86% females) was preformed. Radiographic parameters were noted on Fulcum Bending Radiograph (FBR) and standing coronal/sagittal films preoperatively, immediate postoperative and at two-year follow-up. Flexibility, curve correction rate, and fulcrum bending correction index (FBCI) were calculated. RESULTS: The mean preoperative coronal Cobb’s angles were 58.3° on standing x-ray and 21.9° on FBR (mean FBR flexibility 63.2%). The mean curve correction was 15.2° at immediate postoperative (correction rate: 74.1%; FBCI: 123.4%), and maintained at 18.3° at 2-year follow-up (correction rate: 68.4%; FBCI: 112.5%). 61% of the patients had insignificant change (<5°) in coronal alignment (mean change: 1.1°), while the remaining had a mean change of 6.8°. The trunk list did not change significantly (p=0.368), whereas trunk shift improved on last follow-up (p<0.0001). No clinically significant changes were noted in the sagittal profile. While curve flexibility did not predict loss of correction, skeletally mature patients had a 6-fold higher risk of losing curve correction (95% CI:1.3-27.3). CONCLUSION: This study demonstrated satisfactory maintenance of curve correction by low implant density constructs, such as the ALSS. However, skeletal maturity seemed to affect the correction attained. This could be due to a longer standing deformity and less elastic tissue in a mature patient, needing stronger and possibly more fixation points.