Does Pedicle Screw Length Impact Fusion and Perioperative Complications in 1-level Minimally Invasive Lumbar Fusion: A Comparative Cohort Study

Introduction: We sought to demonstrate that patients who underwent single-level minimally invasive transforaminal interbody fusion (misTLIF) with bicortical pedicle screw instrumentation have improved fusion rates with no increase in perioperative complications.

Methods: We retrospectively reviewed consecutive adults who underwent elective misTLIF from 2018-2019. Patients were followed up at 6 months and 1 year. Screw length was determined by vertebral body (VB)% (screw length/anterior-posterior VB length). The positive and negative predictive values (PPV and NPV) for pseudoarthrosis were measured for different VB% thresholds. VB% with the highest PPV and NPV was used as the cut-off. The primary outcome was fusion determined by the Suk Criteria at 150% film magnification. Secondary outcomes were surgical and perioperative complications defined by the Dindo-Clavien classification. We compared groups above and below the VB% cut-off using univariate analysis. Multivariable analysis was used to identify whether the optimal screw length is independently associated with fusion. P values < 0.05 were considered significant.

Results: Three-hundred-sixty-six patients (154 male) were studied. Sixty-four patients were lost to follow up. The optimal cut-off was determined to be ≥3 screws with >85% VB with a PPV, 77.2%, and a NPV, 23.4%. Operative levels ranged T10 to S1 with L4-5 being the commonest (n=214, 58.5%). There was no significant difference in baseline characteristics between patients with ≥3 (n=317) vs. < 3 (n=49) screws >85% VB. Comparing the groups, there was no significant difference in anytime fusion rate between the ≥3 vs. < 3 screws >85% VB groups [90.1% vs. 90.0%, Δ95% CI -0.10 (-12.1 - 8.80), p= 0.988] and complications. We included VB% cut-off, sex and smoking in the multivariable modeling of anytime fusion and demonstrated no significant independent predictor.

Conclusion : Despite the lack of fusion benefits associated with longer pedicle screw placement, it is a safe practice with no increase in complication rate.