title: Risk factors for L5-S1 disk height reduction after lumbar posterolateral floating fusion surgery.
abstract: METHODS
  This is a retrospective study.
  
  
  OBJECTIVE
  To investigate the risk factors for radiographic L5-S1 disk height reduction after lumbar posterolateral floating fusion surgery.
  
  
  BACKGROUND
  We investigated data from 86 patients (45 men) who underwent posterolateral floating fusion surgery from 2007 to 2010. The follow-up was from 2 to 6 years. The mean age of the patients was 65.4 years.
  
  
  METHODS
  L5-S1 disk height was calculated and >2 mm reduction was defined as significant. Age, sex, height, weight, body mass index, number of fused levels, grade of disk degeneration, disk height and diameter, sacrolumbar alignment, alignment of fused level, achievement of union, and proximal adjacent segment disorder at final follow-up were compared. Univariate and multivariate logistic regressions were performed.
  
  
  RESULTS
  L5-S1 disk height reduction occurred in 14 patients (30.2%). The number of fused levels was significantly greater (1.8±0.8 vs. 1.4±0.6) in patients without disk height reduction. Radiology showed a significant change of L1-S1 sacrolumbar alignment after surgery in patients without disk height reduction (0.3±6.6 vs. -4.5±7.6 degrees). The height of the disk posterior to the L5-S1 intervertebral disk before surgery was significantly greater (7.3±2.1 vs. 6.1±2.1 mm) in patients without disk height reduction. In multivariate logistic regression analysis, fusion of >3 levels was a significant risk factor for L5-S1 disk height reduction.
  
  
  CONCLUSIONS
  In posterolateral floating fusion surgery, there was a higher risk of L5-S1 disk height reduction and consequent foraminal stenosis in patients with multiple-level fusion. Surgical methods and fusion levels should be chosen after considering their association with L5-S1 disk height reduction.
authors: *Department of Orthopaedic Surgery, Kitasato University, School of Medicine, Kanagawa †Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba ‡Department of Orthopaedic Surgery, Teikyo University Chiba Medical Center, Chiba, Japan.
authors: Gen
authors: G
authors: Inoue
authors: Masashi
authors: M
authors: Takaso
authors: Masayuki
authors: M
authors: Miyagi
authors: Hiroto
authors: H
authors: Kamoda
authors: Tetsuhiro
authors: T
authors: Ishikawa
authors: Toshiyuki
authors: T
authors: Nakazawa
authors: Takayuki
authors: T
authors: Imura
authors: Masaki
authors: M
authors: Ueno
authors: Wataru
authors: W
authors: Saito
authors: Kentaro
authors: K
authors: Uchida
authors: Tomoaki
authors: T
authors: Toyone
authors: Kazuhisa
authors: K
authors: Takahashi
authors: Seiji
authors: S
authors: Ohtori
mesh_terms: D000368:Aged; D019299:Decompression, Surgical / Q000009:adverse effects / Q000379:methods; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000601:surgery; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000209:etiology; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008161:Lumbosacral Region / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D012447:Sacrum / Q000000981:diagnostic imaging / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects* / Q000379:methods*; D013130:Spinal Stenosis / Q000000981:diagnostic imaging / Q000209:etiology*; D013168:Spondylolisthesis / Q000000981:diagnostic imaging / Q000601:surgery; D016896:Treatment Outcome