title: Does higher anchor density result in increased curve correction and improved clinical outcomes in adolescent idiopathic scoliosis?
abstract: METHODS
  Retrospective review of prospectively collected data.
  
  
  OBJECTIVE
  To determine whether anchor density is associated with curve correction and patient-reported outcomes.
  
  
  BACKGROUND
  There is limited information as to whether anchor density affects the results of adolescent idiopathic scoliosis surgery.
  
  
  METHODS
  A total of 952 patients with adolescent idiopathic scoliosis met inclusion criteria (Lenke 1, 2, and 5 curves) with predominantly screw constructs (no. of screws/no. of total anchors >75%). Anchor density was defined as the number of screws, hooks, and wires per level fused, with less than 1.54 considered low density. Analysis of covariance was undertaken to determine association of anchor density with percent curve correction, Scoliosis Research Society (SRS), and Spinal Appearance Questionnaire (SAQ) scores, controlling for flexibility, fusion length, demographics, and surgeon.
  
  
  RESULTS
  High- compared with low-anchor density was associated with increased percent curve correction in Lenke 1 curves at 1 year (69% vs. 66% correction, P = 0.0022), controlling for percent preoperative curve flexibility, length of fusion, and sex (model, P < 0.0001). Similar associations held at 2-year follow-up and for Lenke 2 curves. Decreased thoracic kyphosis was found with increased anchor density for Lenke 1 and 2 curve patterns. There were no associations found between anchor density and Lenke 5 curves. For Lenke 1 curve patterns at 2 years postoperatively, in the high- versus low-anchor density cohorts, there were statistically higher SRS Activity (4.3 vs. 4.2, P = 0.019), Appearance (4.3 vs. 4.1, P = 0.0005), Satisfaction (4.5 vs. 4.3, P = 0.028), and Total scores (4.3 vs. 4.2; P = 0.024). Similarly, the SAQ Appearance score at 1 year similarly was improved in the high-anchor density group (high: 14.1 vs. low: 15.0, P = 0.03) for Lenke 1 curve patterns only.
  
  
  CONCLUSIONS
  For Lenke 1 and 2 curve patterns, improved percent correction of major coronal curve was noted in the high-screw density cohort. Although statistical significance was reached, it is unclear whether screw density resulted in clinically significant differences in patient-reported outcomes.
authors.affiliation: *Mayo Clinic, Rochester, MN †University of Minnesota, Minneapolis, MN; ‡PhDx Systems, Inc., Albuquerque, NM; §Texas Scottish Rite Hospital, Dallas, TX; and ¶Children's Hospital, Boston, MA. A complete list of the members of the Minimize Implants Maximize Outcomes Study Group is given in the "Acknowledgment" section.
authors.forename: A Noelle
authors.initials: AN
authors.lastname: Larson
authors.forename: David W
authors.initials: DW
authors.lastname: Polly
authors.forename: Beverly
authors.initials: B
authors.lastname: Diamond
authors.forename: Charles
authors.initials: C
authors.lastname: Ledonio
authors.forename: B Stephens
authors.initials: BS
authors.lastname: Richards
authors.forename: John B
authors.initials: JB
authors.lastname: Emans
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Sucato
authors.forename: Charles E
authors.initials: CE
authors.lastname: Johnston
mesh_terms: D000293:Adolescent; D000328:Adult; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000601:surgery; D012189:Retrospective Studies; D012600:Scoliosis / Q000601:surgery*; D013123:Spinal Fusion / Q000379:methods; D053441:Suture Anchors; D016896:Treatment Outcome