Letter re: Letter to the Editor - Global Spine in Response to Fushimi et al

We read with great interest the recent publication in the Global Spine Journal by Fushimi et al entitled “Transforaminal Lumbar Interbody Fusion with Double Banana Cages: Clinical Evaluation and Finite Element Model Analysis.” The authors conducted a finite element analysis on the use of sequentially nested interbody spacers inserted through a transforaminal corridor to achieve interbody arthrodesis and presented the clinical outcomes of 34 patients. ¹ We agree with the authors on the importance of occupying as much of the interbody space with a cage as possible to minimize the risk of subsidence and increase the rate of arthrodesis.

Nonetheless, we are concerned with the authors’ statement, “This is the first study to biomechanically evaluate TLIF using double banana-shaped cages.” We reported similar findings from our biomechanical analysis of nested semicurved interbody cages in our article entitled, “Biomechanics of nested transforaminal lumbar interbody cages.” ² We reported flexibility and compression testing data that compared nested interbody cages to single interbody cages. The results revealed a significant increase in compressive stiffness and a decrease in the flexibility of the construct while maintaining larger foraminal heights. We also reported that the nested interbody technique increased surface area coverage from 19.4% to 36.6%, diminishing the risk of subsidence.

At the end of their recently published paper in Global Spine Journal, Fushimi et al discuss the technical nuances of the nested approach. The authors aptly point out the technical challenges of the nested interbody technique. In the book, Minimally Invasive Surgery–A Primer. Chapter 4: Minimally Invasive Transforaminal Lumbar Interbody Fusion (TLIF) comprehensively reviews the technical nuances of sequential insertion of nested interbody cages. ³ We invite Fushimi and colleagues to review these resources as they explore the value of nested interbody spacers in TLIF, and we trust they will include these references in future publications examining the nested interbody approach. As the medical literature continues to expand at an exponential rate, concepts and ideas that have been previously published may escape the notice of authors as they prepare their work for publication. What appears to be novel and unpublished has indeed been studied, reviewed, and published. We are reminded of the wisdom found in the book of Ecclesiastes, “What has been will be again, what has been done will be done again; there is nothing new under the sun” (Eccles. 1:9).

We commend Fushimi and colleagues for advancing the transforaminal interbody technique. Their publication contributes to the growing recognition that there is considerable interbody grafting surface area accessible via a transforaminal corridor that our colleagues performing transpsoas approaches have capitalized on for almost 2 decades. As surgeons attempting to optimize patient outcomes and minimize complications, we need to expand into that often unused and neglected space through the transforaminal corridors. The nested interbody technique enables the surgeon to adhere to the principles Cloward espoused in 1953 ⁴ : to fill as much of the interbody space as possible with structural graft.