title: Defining the number and type of fixation anchors for optimal main curve correction in posterior surgery for adolescent idiopathic scoliosis.
abstract: The number and type of fixation anchors to use during posterior surgery for adolescent idiopathic scoliosis (AIS) is still debated, and the relationship with curve correction remains unclear.
  
  
  
  This study aimed to determine the number and type of fixation anchors associated with optimal curve correction following posterior surgery for AIS.
  
  
  
  A retrospective study of the relationship between fixation anchors and main curve correction in AIS surgery was carried out.
  
  
  
  A cohort of 137 AIS patients operated from a posterior-only approach using hooks and pedicle screws comprised the study sample.
  
  
  
  Correction of the main scoliotic curve was the outcome measure.
  
  
  
  Implant density (ID) was defined as the number of fixation anchors divided by the number of available anchor sites within the main curve. Pedicle screw ratio (PSR) was defined as the number of pedicle screws divided by the total number of fixation anchors within the main curve. Multiple linear regressions were performed to analyze the influence of ID and PSR on main curve correction, while taking into account age, gender, curve type, preoperative main Cobb angle, main curve reducibility, number of fused levels, and number of levels within the main curve.
  
  
  
  Main coronal curve correction was significantly related only to ID for all patients and for the subgroup of patients with a main thoracic curve. Constructs with an ID ≥70% and <90% provided a correction similar to that obtained with an ID ≥90%. However, main coronal curve correction was inferior for constructs with an ID <70%, when compared with constructs with ID ≥90%. Implant density and PSR were not related to the change in thoracic kyphosis in the multiple linear regressions.
  
  
  
  Implant density is an important predictor of main coronal curve correction in posterior surgery for AIS. Increasing the number of fixation anchors within the main curve-rather than favoring screws over hooks-can lead to better correction in the coronal plane. However, after reaching an ID of ≥70% in the main curve, adding fixation anchors is not likely to result in significantly greater correction of the main curve in the coronal plane.
authors.affiliation: Department of Surgery, Faculty of Medicine, University of Montreal, C.P. 6128, succursale Centre-ville, Montréal, Québec, H3C 3J7, Canada; Department of Surgery, CHU Sainte-Justine, 3175 Côte-Sainte-Catherine, Montréal, Québec, H3T 1C5, Canada; Department of Surgery, Hôpital du Sacré-Coeur de Montreal, 5400 boulevard Gouin Ouest, Montreal, Quebec, H4J 1C5, Canada. Electronic address: macthiong@gmail.com.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Mac-Thiong
authors.affiliation: College of Medicine, University of Saskatchewan, 1121 College Drive, Saskatoon, S7N 0W3, Canada.
authors.forename: Sameh
authors.initials: S
authors.lastname: Ibrahim
authors.affiliation: Department of Surgery, Faculty of Medicine, University of Montreal, C.P. 6128, succursale Centre-ville, Montréal, Québec, H3C 3J7, Canada; Department of Surgery, CHU Sainte-Justine, 3175 Côte-Sainte-Catherine, Montréal, Québec, H3T 1C5, Canada; Department of Surgery, Hôpital du Sacré-Coeur de Montreal, 5400 boulevard Gouin Ouest, Montreal, Quebec, H4J 1C5, Canada.
authors.forename: Stefan
authors.initials: S
authors.lastname: Parent
authors.affiliation: Department of Surgery, Faculty of Medicine, University of Montreal, C.P. 6128, succursale Centre-ville, Montréal, Québec, H3C 3J7, Canada; Department of Surgery, CHU Sainte-Justine, 3175 Côte-Sainte-Catherine, Montréal, Québec, H3T 1C5, Canada.
authors.forename: Hubert
authors.initials: H
authors.lastname: Labelle
mesh_terms: D000293:Adolescent; D001863:Bone Screws / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D011183:Postoperative Complications; D012600:Scoliosis / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*
keywords: Adolescent idiopathic scoliosis; Hooks; Pedicle screws; Spinal deformity; Spinal fusion; Spinal instrumentation; Spine; Surgery