Letter to the Editor Concerning “Trabecular Bone Remodeling as a New Indicator of Osteointegration after Posterior Lumbar Interbody Fusion.” by Segi et al.

To the Editor,

We read with great interest the article by Segi et al ¹ on the use of trabecular bone remodeling (TBR) as a new indicator of osteointegration after posterior lumbar interbody fusion. TBR is a promising clinical finding that can guide early stage bone fusion. However, we have some concerns regarding this study.

First, the authors evaluated TBR only with coronal images. To prove the utility of TBR as a new marker of bone fusion, it is essential that it be confirmed in all cross-sections. We believe that the position of the TBR may cause differences in bone union and bone healing. For example, anteriorly located TBR appears to have a better bone healing rate. We therefore believe it is important to determine the correlation between the location of TBR appearance and pedicle screw loosening.

Second, there was no significant difference in the T-score or preoperative osteoporosis medication use between the Early TBR positive and negative groups. Previous studies have shown that osteoporotic patients show bone fusion failure and delayed fusion.^2,3 We would expect that TBR would be less likely to occur as reactive osteosclerosis in cases with very low bone density or low bone metabolic turnover because the cage would subside. It would be interesting to discover whether the Early TBR positivity rate is lower or whether TBR appearance is delayed in osteoporotic patients (T-score < -2.5 SD) compared to normal controls.

Third, polyetheretherketone (PEEK) has a stiffness comparable to that of cancellous bone, whereas titanium and tantalum are much more stiff than cortical bone. Although the authors suggested that differences in cage architecture affected early TBR positivity, it is possible that the difference in cage stiffness would have occurred as a response to surrounding osteosclerosis, which may explain the difference in early TBR positivity.

Fourth, nonunion is associated with implant-related problems, such as rod breakage, cage subsidence, and screw loosening, which results in clinical symptoms such as back and leg pain. ⁴ Regarding the relationship between TBR and clinical symptoms, the authors reported that the Japanese Orthopaedic Association (JOA) total score showed no difference in the presence or absence of early TBR positivity. We would like to conduct a detailed analysis of the relationship between TBR and back pain, leg pain, and ADL items in the JOA.

Finally, we would like to know the authors' view on TBR, which we consider to be a lumbar spine response equivalent to Spotwelds, which indicates biological fixation of the femoral implant in total hip arthroplasty. ⁵

We believe that TBR will be a useful evaluation method for clinicians. We look forward to the authors’ answers to our questions regarding the development of TBR.

ORCID iD

Masatsugu Tsukamoto https://orcid.org/0000-0003-0688-0451