Demographic and Radiographic Predictors of Subsequent Fusion Within 2 Years of Isolated Posterior Lumbar Decompression

INTRODUCTION: Isolated posterior lumbar decompression (PLD) is commonly performed for degenerative indications. However, the various factors that predict revision surgery for subsequent fusion remain poorly understood. To this end, the purpose of the current study was to investigate demographic and lumbar imaging findings at the time of PLD that are associated with subsequent fusion. METHODS: Adult patients who underwent isolated 1-2-level PLD between L3-S1 (2014 to 2020) were retrospectively identified. Subsequent fusion within 2 years was determined. Preoperative lumbar magnetic resonance imaging (MRI) was reviewed for (1) sagittally aligned facet (SAF) joints, (2) facet tropism, (3) facet degeneration, (4) disk height, and (5) Pfirrmann grade. Radiology reports were used to categorize the foraminal stenosis severity. Associations between MRI findings before PLD and the need for revision surgery for fusion were investigated using multivariable logistic regression. RESULTS: Among the 202 PLD patients, 21.3% underwent fusion within 2 years. Patients requiring fusion had a higher Charlson comorbidity index (2.07 ± 2.19 versus 1.30 ± 1.73, P = 0.023). No differences were observed in facet tropism, SAF joints, disk height, or stenosis severity between the subsequent fusion and no fusion groups. Patients who did not undergo fusion had higher average facet degeneration scores (1.90 ± 0.76 versus 1.64 ± 0.71, P = 0.030) and a greater proportion of Pfirrmann grade 5 disks (37.8% versus 18.6%, P = 0.013). Multivariable regression identified CCI as the only independent predictor of subsequent fusion (odds ratio: 1.32, cI, 1.03 to 1.72, P = 0.034). CONCLUSION: This study found that higher CCI at the time of PLD is an independent predictor of requiring fusion within 2 years. Increased lumbar degeneration alone was not associated with a greater risk of fusion. Decreased remaining motion, lower functional demands, or a greater propensity for autofusion may have lowered the need for subsequent fusion among these PLD patients with greater degeneration. Further research is needed to support these results.