title: Spinal Implant Density and Postoperative Lumbar Lordosis as Predictors for the Development of Proximal Junctional Kyphosis in Adult Spinal Deformity.
abstract: OBJECTIVE
  To evaluate spinal implant density and proximal junctional kyphosis (PJK) in adult spinal deformity (ASD).
  
  
  METHODS
  Consecutive patients with ASD receiving ≥5 level fusions were retrospectively analyzed between 2007 and 2010.
  
  
  METHODS
  ASD, elective fusions, minimum 2-year follow-up.
  
  
  METHODS
  age <18 years, neuromuscular or congenital scoliosis, cervical or cervicothoracic fusions, nonelective conditions (infection, tumor, trauma). Instrumented fusions were classified by the Scoliosis Research Society-Schwab ASD classification. Statistical analysis consisted of descriptives (measures of central tendency, dispersion, frequencies), independent Student t tests, χ2, analysis of variance, and logistic regression to determine association of implant density [(number of screws + number of hooks)/surgical levels of fusion] and PJK. Mean and median follow-up was 2.8 and 2.7 years, respectively.
  
  
  RESULTS
  Eighty-three patients (17 male, 66 female) with a mean age of 59.7 years (standard deviation, 10.3) were analyzed. Mean body mass index (BMI) was 29.5 kg/m2(range, 18-56 kg/m2) with mean preoperative Oswestry Disability Index of 48.67 (range, 6-86) and mean preoperative sagittal vertical axis of 8.42. The mean levels fused were 9.95 where 54 surgeries had interbody fusion. PJK prevalence was 21.7%, and pseudoarthrosis was 19.3%. Mean postoperative Oswestry Disability Index was 27.4 (range, 0-74). Independent Student t tests showed that PJK was not significant for age, gender, BMI, rod type, mean postoperative sagittal vertical axis, or Scoliosis Research Society-Schwab ASD classification; but iliac fixation approached significance (P = 0.077). Implant density and postoperative lumbar lordosis (LL) were predictors for PJK (P = 0.018 and 0.045, respectively). Controlling for age, BMI, and gender, postoperative LL (not implant density) continued to show significance in multivariate logistic regression model.
  
  
  CONCLUSIONS
  PJK, although influenced by a multitude of factors, may be statistically related to implant density and LL.
authors.affiliation: Division of Pediatric Neurosurgery, Phoenix Children's Hospital, Phoenix, Arizona, USA. Electronic address: jmcclendon@phoenixchildrens.com.
authors.forename: Jamal
authors.initials: J
authors.lastname: McClendon
authors.affiliation: Department of Neurological Surgery, Brigham and Women's Hospital, Harvard School of Medicine, Boston, Massachusetts, USA.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Smith
authors.affiliation: Department of Neurological Surgery, Northwestern Memorial Hospital, Northwestern Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Sugrue
authors.affiliation: Department of Neurological Surgery, Northwestern Memorial Hospital, Northwestern Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Sara E
authors.initials: SE
authors.lastname: Thompson
authors.affiliation: Howell Allen Clinic, Nashville, Tennessee, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: O'Shaughnessy
authors.affiliation: Department of Neurological Surgery, Northwestern Memorial Hospital, Northwestern Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Tyler R
authors.initials: TR
authors.lastname: Koski
mesh_terms: D000368:Aged; D001863:Bone Screws / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D016268:Internal Fixators / Q000706:statistics & numerical data*; D007738:Kyphosis / Q000453:epidemiology*; D016015:Logistic Models; D008141:Lordosis / Q000453:epidemiology*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000453:epidemiology*; D015995:Prevalence; D012189:Retrospective Studies; D012307:Risk Factors; D013122:Spinal Diseases / Q000601:surgery*; D013123:Spinal Fusion; D013904:Thoracic Vertebrae / Q000601:surgery*
keywords: Adult spinal deformity; Implant density; Lumbar lordosis; Proximal junctional kyphosis