title: Correction of moderate (<70 degrees) Lenke 1A and 2A curve patterns: comparison of hybrid and all-pedicle screw systems at 2-year follow-up.
abstract: BACKGROUND
  Multiple reports have demonstrated the superiority of all-pedicle screw constructs, over hybrid and hook constructs, for severe sagittal and coronal deformities (>70 degrees) and have made anterior spinal releasing unnecessary for almost all spinal deformities. However, for lesser deformities, specifically coronal deformities <70 degrees, published studies have not been able to consistently demonstrate clinical superiority of all-pedicle screw constructs over hook or hybrid constructs.
  
  
  METHODS
  A prospective, multicenter database on AIS identified patients with <70 degrees main thoracic (MT) curves surgically treated with a posterior spinal fusion. Inclusion criteria were: Lenke 1A and 2A curve patterns, neurologically normal, primary surgery only, and at least 13 years of age at surgery or be Risser 3 or greater and a construct consisting of all-pedicle screws (PS) or hybrid instrumentation. Minimum follow-up was 2 years postoperative. Patients were excluded if surgeries included any releases (laminectomies, ligament releases, or osteotomies), which may increase curve flexibility.
  
  
  RESULTS
  A total of 101 patients satisfied the criteria for inclusion: PS (n=53) and hybrid (n=48). Preoperative patient data, preoperative curve characteristics, and operative data were similar between the 2 groups. Postoperative thoracic coronal Cobb demonstrated PS had better proximal thoracic (PT) and MT correction, MT Cobb correction % and correction index than hybrid. Interestingly there were no differences in correction index/fixation point between the 2 groups, indicating PS constructs achieved better correction due, at least in part, to the greater number of spine fixation points. Lower instrumented vertebrae tilt and rotational correction was better in the PS group than hybrid. At 2-year follow-up PS had better absolute forced expiratory volume in 1 second values, trunk shift, and total scoliosis appearance questionnaire than hybrids. T5-T12 sagittal alignment was unchanged at 2-year follow-up for PS versus increased kyphosis in hybrids.
  
  
  CONCLUSIONS
  All-pedicle screw systems had better coronal correction, lower instrumented vertebrae tilt, MT scoliometer measurements and scoliosis appearance questionnaire total measures than hybrid constructs. The improved coronal correction in the PS group is likely due, in part, to the higher number of spine fixation points than used in the hybrid groups.
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St Louis, MO, USA. luhmanns@wustl.edu
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Luhmann
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Lenke
authors.forename: Mark
authors.initials: M
authors.lastname: Erickson
authors.forename: Keith H
authors.initials: KH
authors.lastname: Bridwell
authors.forename: B Stephens
authors.initials: BS
authors.lastname: Richards
mesh_terms: D000293:Adolescent; D001863:Bone Screws; D016208:Databases, Factual; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume; D006801:Humans; D016268:Internal Fixators; D008297:Male; D011446:Prospective Studies; D012600:Scoliosis / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D011795:Surveys and Questionnaires; D013904:Thoracic Vertebrae / Q000601:surgery*; D016896:Treatment Outcome