Risk Factors Associated With Revision Microdiscectomy or Subsequent Spinal Fusion Within Two Years of Index Lumbar Microdiscectomy

Study Design. Retrospective review of insurance claims and electronic medical records of a major blended health organization in the eastern United States. Objective. Primary objective was to report rates of revision microdiscectomy and fusion within two years of index lumbar microdiscectomy. Secondary objectives were to identify patient characteristics and comorbidities predictive for revision surgeries. Summary of Background Information. Incidence of disc reherniation after lumbar microdiscectomy ranges from 3% to 18%. Although rates of revision microdiscectomy are well reported, rates of fusion after index microdiscectomy and risk factors for subsequent fusion beyond history of prior discectomy warrants further investigation. Methods. Retrospective review of health insurance claims data for index lumbar microdiscectomy between January 2016, and December 2019. Rates of revision microdiscectomy and fusion within two years were reported, and cohort demographics and Charlson Comorbidity Index (CCI) comorbidities were analyzed using Pearson χ 2 analyses and Fisher exact tests. Time-to-event modeling and multivariate Cox proportional hazards regression assessed for predictors of revision surgery. Results. The full sample consisted of 8158 members. The rate of revision microdiscectomy was 3.5% within one year and 5.5% within two years of index surgery. The rate of fusion was 2.9% within one year and 6.6% within two years of index surgery. Age 40 to 59 ( P <0.001), female sex ( P =0.024), and presence of ≥1 CCI comorbidities ( P <0.001) were significantly associated with time-to-fusion but not revision microdiscectomy. Increasing CCI score was associated with a significantly greater likelihood of need for fusion (CCI=1, HR 1.35, P =0.045; CCI=2, HR 1.85, P <0.001; CCI ≥ 3, HR 2.47, P <0.001). Conclusion. Rates of revision microdiscectomy and fusion within two years of index lumbar microdiscectomy were 5.5% and 6.6%, respectively. Age 40 to 59 years, female sex, and having ≥1 CCI comorbidity, were significantly predictive of time-to-fusion but not revision microdiscectomy. Having at least one comorbidity increased the likelihood of fusion by 80%.