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

Abstract

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.