Long-Term Incidence of Adjacent Segmental Pathology After Minimally Invasive vs Open Transforaminal Lumbar Interbody Fusion

Dear Editor,

Thank you for your letter regarding our paper “Long-Term Incidence of Adjacent Segmental Pathology After Minimally Invasive vs. Open Transforaminal Lumbar Interbody Fusion.” We appreciate the insightful comments and would like to address the points raised.

Effect of Endplate Characteristics and Implant Design on Reoperation Rates

Question: Yu et al found that endplate characteristics and implant design are related risk factors for the failure of lumbar interbody fusion (LIF) surgery. Our study did not address the effect of patient endplate characteristics and implant design on reoperation rates.

Answer: We acknowledge the importance of endplate characteristics and implant design in the success of LIF surgery. Our study primarily focused on the comparison of adjacent segmental pathology (ASP) rates between minimally invasive (MI) and open transforaminal lumbar interbody fusion (TLIF) procedures. However, in this study, both surgical methods used the same cage design, and a comparative analysis regarding this was not conducted. Future research should indeed consider incorporating detailed analyses of endplate characteristics and implant designs to provide a more comprehensive understanding of factors influencing reoperation rates.^1–3

Stability of Unilateral vs Bilateral Cage

Question: Lynch et al have shown that a bilateral cage can reduce spine pressure and provide greater stability compared to a unilateral cage, which might increase postoperative ASP risk. Why did our study not consider the differences in the stability of unilateral and bilateral cages?

Answer: The focus of our study was on the overall comparison between MI-TLIF and open TLIF regarding ASP rates. In this study, we used unilateral cages for both MI-TLIF and open TLIF, but ensured sufficient autograft bone packing on the contralateral side to promote stability and union. Thank you for your important comment.^4–6

Drawbacks of MI-TLIF due to Insufficient Visualization

Question: MI-TLIF may have important drawbacks affecting long-term clinical outcomes due to insufficient visualization. Bindal et al found that intraoperative EMG monitoring can achieve safer pedicle cannulation in MI-TLIF.

Answer: We acknowledge the potential limitations of MI-TLIF, including challenges related to visualization. Despite these challenges, our study showed that MI-TLIF had comparable long-term outcomes to open TLIF in terms of ASP rates. In our study, we did not use EMG monitoring during MI-TLIF surgery, yet there were almost no complications related with visualization during or after the surgery. We ensured adequate visualization by using a tubular retractor and microscope during decompression and discectomy procedures. Through this, we believe that EMG monitoring may not be highly effective, as adequate visualization can be achieved during MI-TLIF.^7–9

Additional Points from Our Study

• Radiographic ASP (RASP) and Clinical ASP (CASP): Our study found that the RASP rate was significantly different between MI-TLIF and open TLIF groups at the 5-year follow-up but not at the 10-year follow-up. The CASP rate differed significantly in the first year post-surgery but not at the 10-year follow-up.

• Influence of Cranial Facet Violation: We identified cranial facet violation as a significant factor affecting ASP in both MI-TLIF and open TLIF groups. In the open TLIF group, preoperative adjacent segment disc degeneration was also a significant factor.

• Long-term Outcomes: There was no significant difference in the rate of ASP requiring reoperation between the 2 groups at the 10-year follow-up.