Risk Factors Associated with Revision Microdiscectomy and/or Subsequent Fusion within 2 Years of Index Lumbar Microdiscectomy

Introduction: Risk factors and rates of reherniation after microdiscectomy requiring revision microdiscectomy are well reported. Although studies report the rate of subsequent fusion, assessment of risk factors for fusion after index microdiscectomy warrants further investigation. Our objective was to report the rates of revision microdiscectomy and subsequent lumbar fusion within 2 years of index lumbar microdiscectomy, as well as risk factors predictive of additional surgery.

Methods: Health insurance claims data was queried for index surgery for disc herniation with microdiscectomy between January 1, 2016, and December 31, 2019. Validation of data was done using the electronic medical records of members that received care at the hospital network connected to the payor. Time-to-event modeling was used to assess predictors of revision microdiscectomy and subsequent lumbar fusion after initial lumbar microdiscectomy.

Results: The full sample consisted of 8,158 members. The rate of revision microdiscectomy was 3.5% within 1 year and 5.5% within 2 years of index surgery. The rate of subsequent lumbar fusion was 2.9% within 1 year and 6.6% within 2 years of index surgery. Ages 40-59 (p < 0.001), female sex (p = 0.024), and members with ≥ 1 Charlson Comorbidity Index (CCI) comorbidities (p < 0.001) were significantly associated with time-to-fusion but not time-to-revision microdiscectomy. Increasing CCI score was associated with a significantly greater likelihood of need for subsequent fusion (CCI score = 1, HR 1.35, p = 0.045; CCI score = 2, HR 1.85, p < 0.001; CCI score ≥ 3, HR 2.47, p < 0.001). Twelve CCI comorbidities, including hemi-/paraplegia, peripheral vascular disease, cerebrovascular disease, and congestive heart failure, were significantly (p < 0.001) associated with time-to-fusion. Only myocardial infarction (p < 0.001), metastatic cancer (p = 0.018), and mild liver disease (p = 0.033) were significantly predictive for time-to-revision microdiscectomy.

Conclusion : Patients undergoing index lumbar microdiscectomy required revision microdiscectomy or subsequent fusion at rates similar to those previously published. Age 40-59 years, female sex, and having ≥ 1 CCI comorbidity, were significantly predictive of time-to-fusion but not time-to-revision microdiscectomy. The presence of at least one comorbidity increased the likelihood of subsequent fusion by 80%.