TO THE EDITOR: We found the article by Matsukawa et al.1 quite interesting, with its conclusion that the cutoff value of the screw insertion depth for achieving bone fusion using the cortical bone trajectory technique is 40% in the vertebral body, which indicates that using longer screws and inserting them deeper into the vertebral body can achieve both anchor strengthening and load sharing within the vertebral body, leading to successful bone fusion (Matsukawa K, Yanai Y, Fujiyoshi K, et al. Depth of vertebral screw insertion using a cortical bone trajectory technique in lumbar spinal fusion: radiological significance of a long cortical bone trajectory. J Neurosurg Spine. 2021;35[5]:601-606). While we completely agree with this conclusion, we have some concerns regarding the radiographic evaluation.
First, in addition to bone fusion, it may have been good to evaluate vertebral endplate cysts, which can be a predictor of pseudarthrosis caused by delayed bone fusion due to micromotion or poor initial fixation.2 Vertebral endplate cysts are frequent, are simpler and easier to evaluate than bone fusion, and may have provided new insights to compensate for the drawback of the small number of non-bony fusion cases in their study.
Second, although we totally agree with the use of Hounsfield units for osteoporosis assessment, we would like to suggest a different region of interest (ROI). Since the authors evaluated loosening of the pedicle screw, the ROI of the pedicle screw trajectories should be evaluated. In contrast, for evaluating osteoporosis, placement of the trabecular ROI at the anterior-middle vertebral level is recommended over the cephalad or caudal3 to avoid distortion of attenuation measurements due to osteosclerosis around the vertebral endplates or posterior venous plexus.
Finally, as the authors also mentioned, it may have been better to investigate the timing of bone fusion. Initial biomechanical stability via posterior fixation until 6 months after posterior lumbar interbody fusion is essential for obtaining osseointegration at the intervertebral cages.4 Examining the period of bone fusion may provide new findings to confirm the strong initial fixation of this screw insertion technique.
We would like the authors to verify the efficacy of this technique with regard to vertebral endplate cysts, the area of the ROI, and the bony fusion period.
Disclosures
The authors report no conflict of interest.
References
- 1↑
Matsukawa K, Yanai Y, Fujiyoshi K, Kato T, Yato Y. Depth of vertebral screw insertion using a cortical bone trajectory technique in lumbar spinal fusion: radiological significance of a long cortical bone trajectory. J Neurosurg Spine. 2021;35(5):601–606.
- 2↑
Tanida S, Fujibayashi S, Otsuki B, et al. Vertebral endplate cyst as a predictor of nonunion after lumbar interbody fusion: comparison of titanium and polyetheretherketone cages. Spine (Phila Pa 1976).2016;41(20):E1216–E1222.
- 3↑
Lee BJ, Koo HW, Yoon SW, Sohn MJ. Usefulness of trabecular CT attenuation measurement of lumbar spine in predicting osteoporotic compression fracture: is the L4 trabecular region of interest most relevant? Spine. (Phila Pa 1976).2021;46(3):175–183.
- 4↑
Makino T, Takanaka S, Sakai Y, Yoshikawa H, Kaito T. Impact of mechanical stability on the progress of bone on growth on the frame surfaces of a titaniumcoated PEEK cage and a 3D porous titanium alloy cage: in vivo analysis using CT color mapping. Eur Spine J. 2021;30(5):1303–1313.
