Letter to the Editor: Risk Factors Affecting Cage Retropulsion into the Spinal Canal Following Posterior Lumbar Interbody Fusion: Association with Diffuse Idiopathic Skeletal Hyperostosis.

Dear Editor,

We read with great interest the recent study by Kato et al. [1] assessing the risk factors affecting cage retropulsion into the spinal canal following posterior lumbar interbody fusion: association with diffuse idiopathic skeletal hyperostosis. We appreciate the author’s efforts to highlight complications on this crucial topic. However, we wish to put our few queries and want to know the author’s input, so that message from this study is presented with greater clarity.

1. Did the location of cages (anterior/posterior) and undersized/lesser height cages have any effect in your study on cage retropulsion as reported by other authors [2]?

2. Does the rod system used in the study was titanium or polyether ether ketone? What is the author’s recommendation from these two and does it have any effect on outcome [3]?

3. What was the status of interbody fusion after single or double cage, did the number of cages alter the time and quality of fusion, and did the delayed fusion also contribute to delayed retropulsion?

4. Do the authors suggest using a double cage even in poor overall condition patients, as a single cage was associated with more incidences of retropulsion in this study [4]?

5. The same size cage was used in this study at the time of revision surgery. Does the use of a bigger size cage make any difference, as suggested by a few authors [2]?