Risk-equivalent T-score Adjustment for Using Lumbar Spine Trabecular Bone Score (TBS): the Manitoba BMD Registry

Introduction: The aim of this study is to develop an approach for using TBS in clinical practice based upon a "risk-equivalent" adjustment to the BMD T-score.

Methods: We identified 45,185 women age 40 years and older with baseline spine and hip DXA, TBS, and FRAX probabilities including femoral neck BMD. Incident major osteoporotic fractures (MOF, n = 3925) were identified from population-based health services data (mean follow-up 7.4 years comprising 335,910 person-years). Cox proportional hazards models adjusted for age and BMI were first used to estimate the risk for MOF from BMD T-score alone, then after including TBS and a multiplicative age interaction term. From the parameter estimates, we developed a TBS offset to the BMD T-score based upon change in TBS that would give the same risk as a unit change in BMD T-score for the femoral neck, total hip, and lumbar spine.

Results: All BMD measurements, TBS, and the age interaction term independently predicted MOF (p < 0.001). Measures of risk stratification and model fit were improved for the TBS-adjusted BMD T-score versus the unadjusted BMD T-score (p < 0.001). There was a high level of agreement between MOF probability estimated from TBS-adjusted MOF FRAX probability and FRAX probability using the "risk-equivalent" femoral BMD T-score: MOF probability r = 0.98, slope = 1.02, intercept = - 0.3; hip probability r = 0.95, slope = 1.07, intercept = 0.0.

Conclusions: The BMD-independent effect of lumbar spine TBS on fracture risk can be estimated as a simple offset to the BMD T-score.