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

Abstract

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.