title: Cage migration in spondylolisthesis treated with posterior lumbar interbody fusion using BAK cages.
abstract: METHODS
  A retrospective study was conducted to review the complication of cage migration in posterior lumbar interbody fusion (PLIF) with the Bagby and Kuslich method.
  
  
  OBJECTIVE
  To review and analyze cage migration in spondylolytic spondylolisthesis treated with PLIF using paired BAK cages.
  
  
  BACKGROUND
  PLIF with cages has been introduced to treat spondylolisthesis for several years. Theoretically, this technique offers several advantages. BAK system gained popularity rapidly in recent few years. However, most reports focused on clinical effects; only a few studies had been carried out to review complications. As one of the major complications, cage migration into vertebral body or spinal canal may result in severe or disastrous consequence, only a few reports discussed on this issue.
  
  
  METHODS
  From October 1997 to August 2000, 118 patients with spondylolytic spondylolisthesis underwent single-level PLIF using paired BAK cages filled with morselized autogenous bone; 88 of them were followed up for more than 2 years with an average of 3 years and 10 months. The complication of cage migration and its sequelae were reviewed.
  
  
  RESULTS
  Three cases of cage retropulsion and four cases of cage subsidence were found in the current study. The rate of cage migration in patients with no posterior instrumentation was significantly higher compared with that rate in those with posterior instrumentation (16.7% vs. 0%). For patients with no posterior instrumentation, 4 of 8 cases with total facetectomy and 3 of 34 cases with partial facetectomy developed cage migration; the rate of cage migration was 16% for patients with preoperative Grade I olisthesis and 17.6% for those with preoperative Grade II olisthesis (P > 0.05). All patients with cage subsidence lost some degree of lumbar lordosis and disc height, 2 of them finally obtained suboptimal fusion, the other 2 developed pseudarthrosis and received additional posterior instrumentation and intertransverse fusion. Two patients with cage retropulsion developed severe lumbar stenosis and have to remove their dislocated cages. The other one received conservative treatment.
  
  
  CONCLUSIONS
  An 8% rate of cage migration was found in the current study, and 4 of 7 cases with cage migration received revision surgery. Several factors may contribute to the cage migration, including lack of posterior instrumentation and total facetectomy. Revision surgery for cage migration was technically challenging.
authors.affiliation: Department of Orthopaedic Surgery, First Affiliated Hospital of Suzhou University, Suzhou, PRC. chenliang1972@hotmail.com
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.forename: Huilin
authors.initials: H
authors.lastname: Yang
authors.forename: Tiansi
authors.initials: T
authors.lastname: Tang
mesh_terms: D000328:Adult; D016025:Bone Transplantation; D020878:Device Removal; D005260:Female; D005471:Fluoroscopy; D005548:Foreign-Body Migration / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000601:surgery*; D006801:Humans; D015994:Incidence; D016268:Internal Fixators / Q000009:adverse effects*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011542:Pseudarthrosis / Q000209:etiology / Q000601:surgery; D012086:Reoperation; D012189:Retrospective Studies; D013123:Spinal Fusion; D013130:Spinal Stenosis / Q000209:etiology / Q000601:surgery; D013168:Spondylolisthesis / Q000000981:diagnostic imaging / Q000601:surgery*