Adjusting Trabecular Bone Score (TBS) for Level-Specific Differences Reduces FRAX®-Based Treatment Reclassification in Patients with Vertebral Exclusions: The Manitoba BMD Registry

Effect of excluding fractured or abnormal vertebrae on the trabecular bone score measurement

Brief rationale: The use of L1-L4 vertebrae, without exclusions, has been recommended for trabecular bone score (TBS) measurements.

MAIN RESULT

Excluding abnormal and fractured vertebrae affected the TBS. Significance of the paper: Fracture or degenerative abnormality may not affect TBS. The preferred action may involve including all levels without exclusions.

PURPOSE

The use of L1-L4 vertebrae, without exclusions, has been recommended for trabecular bone score (TBS) measurements. We aimed to investigate the effect of excluding fractured or abnormal vertebrae from TBS.

METHODS

Dual-energy X-ray absorptiometry images of 2767 participants, including 1080 without excluded vertebrae, 556 with fractured vertebrae, and 1131 with abnormal vertebrae showing a 1.0 T-score difference compared to the adjacent vertebrae, were retrospectively reviewed. Differences between TBS measurements with and without fractured or abnormal vertebrae were evaluated.

RESULTS

Among 1080 participants without excluded vertebrae, TBS was 1.234 at L1, 1.296 at L2, 1.308 at L3, and 1.301 at L4. A significantly higher mean TBS was seen after excluding L1, whereas a significantly lower mean TBS was seen after excluding L2-L4. In the 556 participants with fractured vertebrae, excluding the involved level from the TBS calculation led to a significant difference in the total sample, women, ≥ 70 years old, and overweight subgroups. A significantly higher mean TBS was seen after excluding the fractured L1, whereas a significantly lower mean TBS was seen after excluding fractures at L2-L4. Among the 1131 participants with abnormal vertebrae, excluding the involved level from the TBS led to a significant difference in age, sex, and body mass index subgroups. Excluding abnormal L1 and L4 vertebrae led to a significantly higher and lower mean TBS, respectively.

CONCLUSION

Excluding fractured or abnormal vertebrae led to differences in TBS across various subgroups. Regarding the effect of vertebral level exclusion, the observed differences may be attributed to the systematic intervertebral variation, which is unrelated to any effect from fractures or degenerative abnormalities.

Effects of Lumbar Spine Vertebral Fractures on Trabecular Bone Score (TBS): The Manitoba BMD Registry

Trabecular bone score (TBS) is a BMD-independent risk factor for fracture. During BMD reporting, it is standard practice to exclude lumbar vertebral levels affected by structural artifact. It is uncertain whether TBS is affected by lumbar spine fractures. The current study examined the effect of lumbar spine compression fractures on TBS measurements. We identified 656 individuals with vertebral fractures (mean age 75.8 ± 7.9 years, 90.9% female) who had lumbar spine DXA, TBS measurements from L1-L4 and vertebral fracture assessment (VFA) for identifying vertebral fractures. There were 272 cases with lumbar spine fractures and 384 controls with only thoracic spine fractures. L1 TBS and BMD were significantly greater in those with than without lumbar fractures (p< 0.001) but did not significantly differ for other vertebral levels or for L1-L4 combined. TBS and BMD measurements were then renormalized to remove level-specific differences (denoted rTBS and rBMD). The mean difference (all fractured minus all non-fractured vertebrae) was +0.040 (+3.3%) for rTBS and +0.088 g/cm2 (+9.5%) for rBMD (both p <0.001). The largest effect was for L1 with mean difference +0.058 (+4.9%) for rTBS and +0.098 g/cm2 (+10.6%) for rBMD (both p <0.001). The mean difference between fractured and non-fractured levels for rTBS was +0.028 (+2.4%) for grade 1, +0.036 (+3.0%) for grade 2 and +0.059 (+5.0%) for grade 3 fractures; for rBMD +0.051 (+5.5%), +0.076 (+8.2%) and +0.151 (+16.4%) g/cm2, respectively. The impact of excluding lumbar vertebral levels with fracture from the L1-L4 TBS measurement overall was small (-0.011 [-1.0%]; p<0.001) and was also small for grade 3 fractures (-0.020 [-1.7%]; p<0.001). In summary, TBS is mildly increased by VFA-confirmed lumbar vertebral fractures, but the percentage effect is much smaller (less than half) than seen for BMD and minimally affects TBS measured from L1-L4. This would support the use of L1-L4 without exclusions in individuals with lumbar vertebral fractures.

Clinical Use of Trabecular Bone Score: The 2023 ISCD Official Positions

Osteoporosis can currently be diagnosed by applying the WHO classification to bone mineral density (BMD) assessed by dual-energy x-ray absorptiometry (DXA). However, skeletal factors other than BMD contribute to bone strength and fracture risk. Lumbar spine TBS, a grey-level texture measure which is derived from DXA images has been extensively studied, enhances fracture prediction independent of BMD and can be used to adjust fracture probability from FRAX® to improve risk stratification. The purpose of this International Society for Clinical Densitometry task force was to review the existing evidence and develop recommendations to assist clinicians regarding when and how to perform, report and utilize TBS. Our review concluded that TBS is most likely to alter clinical management in patients aged ≥ 40 years who are close to the pharmacologic intervention threshold by FRAX. The TBS value from L1-L4 vertebral levels, without vertebral exclusions, should be used to calculate adjusted FRAX probabilities. L1-L4 vertebral levels can be used in the presence of degenerative changes and lumbar compression fractures. It is recommended not to report TBS if extreme structural or pathological artifacts are present. Monitoring and reporting TBS change is unlikely to be helpful with the current version of the TBS algorithm. The next version of TBS software will include an adjustment based upon directly measured tissue thickness. This is expected to improve performance and address some of the technical factors that affect the current algorithm which may require modifications to these Official Positions as experience is acquired with this new algorithm.

Adjusting Trabecular Bone Score (TBS) for Level-Specific Differences Reduces FRAX®-Based Treatment Reclassification in Patients with Vertebral Exclusions: The Manitoba BMD Registry

Trabecular bone score (TBS) is a FRAX®-independent risk factor for fracture prediction. TBS values increase from cranial to caudal, with the following mean differences between TBSL1-L4 and individual lumbar vertebrae: L1 -0.093, L2 -0.008, L3 +0.055 and L4 +0.046. Excluding vertebral levels can affect FRAX-based treatment recommendations close to the intervention threshold. We examined the effect of adjusting for level-specific TBS differences in individuals with vertebral exclusions due to structural artifact on TBS-adjusted FRAX-based treatment recommendations. We identified 71,209 individuals aged ≥40 years with TBS and FRAX calculations through the Manitoba Bone Density Program. In the 24,428 individuals with vertebral exclusions, adjusting TBS using these level-specific factors agreed with TBSL1-L4 (mean difference -0.001). We compared FRAX-based treatment recommendations for TBSL1-L4 and for non-excluded vertebral levels before and after adjusting for level-specific TBS differences. Among those with baseline major osteoporotic fracture risk ≥15 %, TBS with vertebral exclusions reclassified FRAX-based treatment in 10.6 % of individuals compared with TBSL1-L4, and was reduced to 7.2 % after adjusting for level-specific differences. In 11,131 patients where L1-L2 was used for BMD reporting (the most common exclusion pattern with the largest TBS effect), treatment reclassification was reduced from 13.9 % to 2.4 %, respectively. Among individuals with baseline hip fracture risk ≥2 %, TBS vertebral exclusions reclassified 7.1 % compared with TBSL1-L4, but only 4.5 % after adjusting for level-specific differences. When L1-L2 was used for BMD reporting, treatment reclassification from hip fracture risk was reduced from 9.2 % to 5.2 %. In conclusion, TBS and TBS-adjusted FRAX-based treatment recommendations are affected by vertebral level exclusions for structural artifact. Adjusting for level-specific differences in TBS reduces reclassification in FRAX-based treatment recommendations.

FRAX® Adjustment Using Renormalized Trabecular Bone Score (TBS) from L1 Alone may be Optimal for Fracture Prediction: The Manitoba BMD Registry

Lumbar spine trabecular bone score (TBS) used in conjunction with FRAX® improves 10-year fracture prediction. The derived FRAX risk adjustment is based upon TBS measured from L1-L4, designated TBSL1-L4-FRAX. In prior studies, TBS measurements that include L1 and exclude L4 give better fracture stratification than L1-L4. We compared risk stratification from TBS-adjusted FRAX using TBS derived from different combinations of upper lumbar vertebral levels renormalized for level-specific differences in individuals from the Manitoba Bone Density Program aged >40 years with baseline assessment of TBS and FRAX. TBS measurements for L1-L3, L1-L2 and L1 alone were calculated after renormalization for level-specific differences. Corresponding TBS-adjusted FRAX scores designated TBSL1-L3-FRAX, TBSL1-L2-FRAX and TBSL1-FRAX were compared with TBSL1-L4-FRAX for fracture risk stratification. Incident major osteoporotic fractures (MOF) and hip fractures were assessed. The primary outcome was incremental change in area under the curve (ΔAUC). The study population included 71,209 individuals (mean age 64 years, 89.8% female). Before renormalization, mean TBS for L1-3, L1-L2 and L1 was significantly lower and TBS-adjusted FRAX significantly higher than from using TBSL1-L4. These differences were largely eliminated when TBS was renormalized for level-specific differences. During mean follow-up of 8.7 years 6745 individuals sustained incident MOF and 2039 sustained incident hip fractures. Compared with TBSL1-L4-FRAX, use of FRAX without TBS was associated with lower stratification (ΔAUC = -0.009, p < 0.001). There was progressive improvement in MOF stratification using TBSL1-L3-FRAX (ΔAUC = +0.001, p < 0.001), TBSL1-L2-FRAX (ΔAUC = +0.004, p < 0.001) and TBSL1-FRAX (ΔAUC = +0.005, p < 0.001). TBSL1-FRAX was significantly better than all other combinations for MOF prediction (p < 0.001). Incremental improvement in AUC for hip fracture prediction showed a similar but smaller trend. In conclusion, this single large cohort study found that TBS-adjusted FRAX performance for fracture prediction was improved when limited to the upper lumbar vertebral levels and was best using L1 alone.

Effects of Severe Lumbar Spine Structural Artifact on Trabecular Bone Score (TBS): The Manitoba BMD Registry

Trabecular bone score (TBS) is a bone mineral density (BMD)-independent risk factor for fracture. During DXA analysis and BMD reporting, it is standard practice to exclude lumbar vertebral levels affected by structural artifact. Although TBS is relatively insensitive to degenerative artifact, it is uncertain whether TBS is still useful in the presence extreme structural artifact that precludes reliable spine BMD measurement even after vertebral exclusions. Among individuals aged 40 years and older undergoing baseline DXA assessment from September 2012 to March 2018 we identified three mutually exclusive groups: spine BMD reporting performed without exclusions (Group 1, N=12,865), spine BMD reporting performed with vertebral exclusions (Group 2, N=4867), and spine BMD reporting not performed due to severe structural artifact (Group 3, N=1541). No significant TBS difference was seen for Group 2 versus Group 1 (referent), whereas TBS was significantly greater in Group 3 (+0.041 partially adjusted, +0.043 fully adjusted). When analyzed by the reason for vertebral exclusion, multilevel degenerative changes significantly increased TBS (+0.041 partially adjusted, +0.042 fully adjusted), while instrumentation significantly reduced TBS (-0.059 partially adjusted, -0.051 fully adjusted). Similar results were seen when analyses were restricted to those in Group 3 with a single reason for vertebral exclusions, and when follow up scans were also included. During mean follow-up of 2.5 years there were 802 (4.2 %) individuals with one or more incident fractures. L1-L4 TBS showed significant fracture risk stratification in all groups including Group 3 (P-interaction >0.4). In conclusion, lumbar spine TBS can be reliably measured in the majority of lumbar spine DXA scans, including those with artifact affecting up to two vertebral levels. However, TBS is significantly affected by the presence of extreme structural artifact in the lumbar spine, especially those with multilevel degenerative disc changes and/or instrumentation that precludes reliable BMD reporting.