title: Reoperations after lumbar disc surgery: a population-based study of regional and interspecialty variations.
abstract: METHODS
  A follow-up study using nationwide administrative databases.
  
  
  OBJECTIVE
  To explore rates of reoperation after lumbar disc surgery and their regional and interspecialty variations.
  
  
  BACKGROUND
  In many Western countries, rates of lumbar disc surgery display significant geographic variations suggesting varying treatment criteria among operating surgeons. Few population-based studies have explored the risk of reoperation after disc surgery, and regional or interspecialty variations in the reoperations are unknown.
  
  
  METHODS
  Patients who underwent lumbar spine surgery from January 1, 1987 through December 31, 1995, were identified in the Finnish Hospital Discharge Register. Data on the patients' initial disc operations, subsequent operations, and cause-of-death records were linked using personal identification codes. The Kaplan-Meier method and proportional hazard model were used to analyze risks of reoperation after initial surgery, according to hospital catchment area rates of disc surgery and for neurosurgical and orthopedic patients of university hospitals.
  
  
  RESULTS
  12.3% of 25,359 surgical patients with herniated lumbar discs underwent subsequent lumbar operations corresponding to the cumulative risk of 18.9% in the 9-year follow-up. Reoperation rates increased during the study period with the recent patient cohorts exhibiting risks. The reoperation risk showed a systematic geographic variation: the higher the regional disc surgery rate, the higher the reoperation risk. Overall, neurosurgical patients had a higher reoperation risk than orthopedic patients (relative risk [RR]: 1.57, 95% confidence interval [CI]: 1.17-2.10), but this was not a uniform finding.
  
  
  CONCLUSIONS
  The reoperation risk after disc surgery increased during the study period and was higher in hospital catchment areas with higher overall discectomy rates. The reoperation risks varied among the university hospitals but tended to be higher for neurosurgical rather than for orthopedic patients.
authors.affiliation: National Research and Development Centre for Welfare and Health (STAKES), Health Services Research, Helsinki, Finland. Ilmo.Keskimaki@stakes.fi
authors.forename: I
authors.initials: I
authors.lastname: Keskimäki
authors.forename: S
authors.initials: S
authors.lastname: Seitsalo
authors.forename: H
authors.initials: H
authors.lastname: Osterman
authors.forename: P
authors.initials: P
authors.lastname: Rissanen
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D006761:Hospitals / Q000706:statistics & numerical data; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000453:epidemiology*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008511:Medicine / Q000706:statistics & numerical data*; D008875:Middle Aged; D016016:Proportional Hazards Models; D012042:Registries; D012086:Reoperation / Q000706:statistics & numerical data*; D013038:Specialization