Available online 23 May 2023, 101415

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Lumbar spine trabecular bone score (TBS), a texture measure derived from spine dual-energy x-ray absorptiometry (DXA) images, is a bone mineral density (BMD)-independent risk factor for fracture. Lumbar vertebral levels that show structural artifact are excluded from BMD measurement. TBS is relatively unaffected by degenerative artifact, and it is uncertain whether the same exclusions should be applied to TBS reporting. To gain insight into the clinical impact of vertebral exclusion on TBS, we examined the effect of lumbar vertebral exclusions in routine clinical practice on tertile-based TBS categorization and TBS adjusted FRAX-based treatment recommendations. The study population consisted of 71,209 individuals aged 40 years and older with narrow fan-beam spine DXA examinations and retrospectively-derived TBS. During BMD reporting, 34.3% of the scans had one or more vertebral exclusions for structural artifact. When TBS was derived from the same vertebral levels used for BMD reporting, using fixed L1-L4 tertile cutoffs (1.23 and 1.31 from the McCloskey meta-analysis) reclassified 17.9% to a lower and 6.5% to a higher TBS category, with 75.6% unchanged. Reclassification was reduced from 24.4% overall to 17.2% when level-specific tertile cutoffs from the software manufacturer were used. Treatment reclassification based upon FRAX major osteoporotic fracture probability occurred in 2.9% overall, but in 9.6% of those with baseline risk ≥15%. For treatment based upon FRAX hip fracture probability, reclassification occurred in 3.4% overall, but in 10.4% in those with baseline risk ≥2%. In summary, lumbar spine TBS measurements based upon vertebral levels other than L1-L4 can alter the tertile category and treatment recommendations based upon TBS-adjusted FRAX calculation, especially for those close to or exceeding the treatment cut-off. Manufacturer level-specific tertile cut-offs should be used if vertebral exclusions are applied.

Section snippetsINTRODUCTION

Lumbar spine trabecular bone score (TBS), a grey-level texture measure derived from spine dual-energy x-ray absorptiometry (DXA) images, is a BMD-independent risk factor for fracture1. The use of TBS for guiding patient management is supported by guidelines from several organizations2, 3, 4. Lumbar spine bone mineral density (BMD) is also commonly assessed with DXA since vertebral fractures are the most common site for osteoporotic fracture and spine BMD is predictive of low-trauma fractures

Study population

The study cohort consistent of all individuals registered with Manitoba Health age 40 years or older undergoing initial fan-beam DXA examination of the lumbar spine through the Manitoba BMD Program with retrospectively derived TBS. We excluded from further analysis individuals where lumbar spine BMD could not be assessed or was not felt to be reportable due to extreme structural artifact and/or instrumentation, but we retained those with at least two reportable lumbar vertebral levels. We also

Study population

Table 1 summarizes the baseline population characteristics which included 71,209 individuals, mean age 64.0 years (SD 10.7), majority female (89.8%), mean BMI 26.4 kg/m2 (SD 4.4). Mean FRAX scores without TBS were 10.0% (SD 7.0%) for MOF and 2.3% (SD 3.8%} for hip fracture probability. In the majority of the scans (N=46,781, 65.7%) no vertebral exclusions were required. Among the remaining scans with vertebral exclusions (N=24,428, 34.3%), 16.2% reported three vertebral levels (i.e., one

DISCUSSION

Current guidance assumes that TBS has been derived as a mean of all four lumbar vertebrae (L1-L4) and practitioners should be aware that excluding individual vertebral levels can affect TBS values. In general, the more frequently excluded lower lumbar vertebrae (due to a higher prevalence of age-related degenerative disease) results in an over-representation of upper lumbar levels such as L1-L2 resulting in lower TBS values. The opposite is seen when the calculation of TBS is limited to lower

Roles

Authors' roles: conception, design, data analysis, drafting the article (WDL), interpretation of data (All Authors); critically revising the article for important intellectual content (All Authors); final approval of the version to be published (All Authors); and agreement to be accountable for all aspects of the work (All Authors). WDL had full access to all the data in the study and takes the responsibility for the integrity of the data and the accuracy of the data analysis.

Funding

This study had no external funding body.

Disclosures

William Leslie and Heenam Goel declare no conflict of interest.

Neil Binkley: Nothing to declare for the context of this paper; research funding from Radius; consultant Amgen.

Didier Hans: Co-ownership in the TBS patent. Stock options or royalties: Medimaps Group. Research grants: Amgen, Agnovos, GE Healthcare.

Eugene McCloskey: Nothing to declare for the context of this paper; ad hoc consultancies/ speaking honoraria and/or research funding from Amgen, Bayer, General Electric, GSK, Hologic,

Acknowledgments

The authors acknowledge the Manitoba Centre for Health Policy for use of data contained in the Population Health Research Data Repository (HIPC 2016/2017- 29). The results and conclusions are those of the authors and no official endorsement by the Manitoba Centre for Health Policy, Manitoba Health, Healthy Living, and Seniors, or other data providers is intended or should be inferred. This article has been reviewed and approved by the members of the Manitoba Bone Density Program Committee.

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© 2023 The International Society for Clinical Densitometry. Published by Elsevier Inc.