In which patients does lumbar spine trabecular bone score (TBS) have the largest effect?

Background: Lumbar spine TBS, a texture index derived from lumbar spine dual-energy x-ray absorptiometry (DXA) images, enhances fracture prediction. No studies to date have studied a broad range of clinical variables to determine which patients might experience the greatest benefit from the use of TBS.

Methods: Using the Manitoba BMD Registry, we identified 37,176 subjects with baseline DXA, FRAX®-based fracture probability, lumbar spine TBS, and minimum 5 years of observation. Subgroups considered were based on sex, age, body mass index (BMI), prior fracture, chronic obstructive lung disease (COPD), high alcohol use, rheumatoid arthritis (RA), high glucocorticoid use, osteoporotic femoral neck T-score, number of comorbidities, diabetes, secondary osteoporosis, and prior osteoporosis treatment. Non-traumatic major osteoporotic fractures (MOF, n = 3741) and hip fractures (HF, n = 1008) were identified using population-based health services data. We analyzed baseline TBS using analysis of covariance (ANCOVA). FRAX-adjusted hazard ratios (HR) per SD reduction in TBS were estimated and tested for interactions. Categorical net reclassification improvement (NRI) was estimated using fixed FRAX-based intervention cut-offs.

Results: Adjusted baseline TBS was significantly lower (p ≤ 0.001) for women (-4.2%), osteoporotic hip T-score (-4.0%), COPD (-2.8%), diabetes (-2.6%), high alcohol use (-2.3%), prior fracture (-2.2%), glucocorticoid use (-1.5%), RA (-0.9%) and secondary osteoporosis (-0.8%), whereas recent osteoporosis therapy was associated with greater TBS (+1.5%). HRs per SD reduction in TBS for fracture prediction were larger for age < 65 vs 65+ (MOF p-interaction = 0.004, HF p-interaction < 0.001), without vs with prior fracture (MOF p-interaction = 0.003, HF p-interaction = 0.048), without vs with glucocorticoid use (HF p-interaction = 0.029), lower vs higher comorbidity score (HF p-interaction < 0.001), and without vs with osteoporosis treatment (MOF p-interaction = 0.005). NRI for using the TBS adjustment to FRAX in all subjects was 1.2% for MOF (p = 0.002) and 1.7% for HF (p = 0.016). NRI was greater in subjects age < 65 y (MOF:1.7%, HF:5.6%), no prior fracture (HF: 2.4%), non-osteoporotic T-score (HF: 3.0%), and high glucocorticoid use (MOF: 3.9%).

Conclusion: TBS is sensitive to the effects of multiple risk factors for fracture. TBS-adjusted fracture risk assessment resulted in significant improvements for multiple subgroups.