To the editor,
We read with great interest the recent article by Jang et al. [
1], who demonstrated progressive Hounsfield unit (HU) decline within the fusion construct (FC) after multilevel lumbar fusion, accompanied by a relative HU increase at the upper instrumented level. Their study is valuable because it provides quantitative imaging evidence that the fused segment is not biologically inert after surgery and that long-term stress redistribution may contribute to measurable disuse-related bone loss within the construct.
In our view, the principal strength of this work lies in identifying a clinically relevant postoperative imaging phenotype. More importantly, it creates an opportunity to move beyond documenting bone loss within the FC and toward clarifying how such changes may inform long-term surgical decision-making.
While Jang et al. [
1] clearly demonstrate the value of serial HU assessment, recent evidence suggests that postoperative mechanical risk may not be fully captured by any single bone quality metric. Because the predictive performance of HU, vertebral bone quality, dual-energy x-ray absorptiometry, and quantitative computed tomography appears to vary according to complication type and spinal region, construct-related bone loss may be more meaningfully interpreted within a multimodal and site-specific framework [
2].
From this perspective, future work should not view the FC as a uniform region. Different parts of the construct are exposed to different mechanical environments, and bone remodeling is therefore unlikely to be evenly distributed. A more clinically relevant approach may be to analyze the construct segment by segment, while also focusing on mechanically critical regions such as the pedicle or screw trajectory, cage-adjacent endplate, and posterior fusion mass. Such a strategy may help identify localized zones of weakness that are more directly relevant to implant removal, revision surgery, and long-term postoperative surveillance [
3-
5].
We also believe that the greatest translational value of this work will come from linking imaging changes to hard clinical endpoints. For the practicing spine surgeon, the key question is not simply whether HU declines within the FC, but whether a given magnitude or pattern of decline predicts cage subsidence, screw loosening, fracture after implant removal, or revision complexity [
2,
6,
7]. If construct-related HU loss can be integrated with complementary bone quality measures to define threshold-based risk, the concept introduced by Jang et al. [
1] could evolve into a clinically actionable tool for postoperative surveillance and surgical planning.
Overall, Jang et al. [
1] should be congratulated for opening an important field of investigation. Their findings may represent not the endpoint of postoperative construct assessment, but the foundation for a broader strategy integrating local remodeling, regional fixation biology, and multimodal bone quality evaluation in spine surgery.
NOTES
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Conflict of Interest
The authors have nothing to disclose.
REFERENCES
- 1. Jang HJ, Kim D, Moon BJ, et al. Disuse bone loss in fusion constructs after multilevel lumbar fusion: a computed tomography Hounsfield unit analysis. Neurospine 2026;23:176-86.
- 2. Shang J, Wang C, Li N, et al. Comparative effectiveness of Hounsfield unit, MRI-based bone quality, dual-energy X-ray absorptiometry T -score, and quantitative computed tomography-measured bone mineral density in predicting cage subsidence and screw loosening post-spinal surgery. Int J Surg 2026;112:5014-24.
- 3. Sakai Y, Takenaka S, Matsuo Y, et al. Hounsfield unit of screw trajectory as a predictor of pedicle screw loosening after single level lumbar interbody fusion. J Orthop Sci 2018;23:734-8.
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- 5. Cho JH, Lau D, Ashayeri K, et al. Association between the bone density of posterior fusion mass and mechanical complications after thoracolumbar three-column osteotomy for adult spinal deformity. Spine (Phila Pa 1976) 2023;48:672-82.
- 6. Kim SK, Chung JY, Seo HY, et al. Vertebral compression fracture within a solid fusion mass without trauma after removal of pedicle screws. Spine J 2016;16:e219-23.
- 7. Pennington Z, Mikula AL, Hamouda A, et al. The influence of bone quality and paraspinal musculature on proximal junctional kyphosis failure mode among patients undergoing lumbopelvic fusion terminating at the thoracolumbar junction. J Neurosurg Spine 2025;43:559-68.
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