Letter to the Editor Concerning "Frequency of Change in Assessment from Bony Union to Nonunion after Lumbar Interbody Fusion: A Multicenter Study" by Oba et al.

Letter to the Editor: It was our pleasure to read the article by Oba et al., and we were surprised to find that even with obvious early postoperative bony union, more than a quarter of patients may be in a state of fake union. We agree that careful follow-up is still needed and that weekly teriparatide may be effective in reducing the rate. However, we would like to comment on the authors’ methodology. First, in this study, computed tomography seems to have been performed four times a year, including preoperatively. Considering that this is a very high rate, could the authors have made any effort to reduce the amount of radiation exposure? Second, in addition to bony union, it might have been advisable to evaluate vertebral endplate cysts, which can be a predictor of pseudoarthrosis caused by delayed bone fusion due to micromotion or poor initial fixation. Vertebral endplate cysts are more common, simpler, and easier to evaluate than bony union and may provide new insights on the relationship between the new appearance of cysts and the trend toward increased size and fake union. Third, it is possible that there was no significant difference in the assessment of osteoporosis because the young adult mean (YAM) of the hip was used. Although it might be better to use the YAM of the lumbar spine for the assessment of bone fusion, it should be noted that this YAM is affected by osteophytes and vertebral fractures. Therefore, it would have been better to use the Hounsfield unit of the fixed vertebral body for the evaluation of osteoporosis. Fourth, the results were evaluated with and without osteoporosis drugs, but was there any possibility that the results were altered depending on the contents of the drugs, including bisphosphonate? It is well known that a history of bisphosphonate therapy attenuates the osteogenic effect of teriparatide. Finally, we would like to point out that it may be too early to judge fusion or nonfusion at 6 months postoperatively. Tokuhashi et al. reported that the clear zone around the pedicle screw observed at 6 months postoperatively might show improvement during up to 2 years postoperatively. We would be very interested to know how the fake union increases or decreases at 12 months or 2 years postoperatively. We sincerely hope that the authors will conduct a long-term study.