Spine Fragility Fracture Prediction Using TBS and BMD in Postmenopausal Women: A Bayesian Approach

The trabecular bone score (TBS) estimates bone microarchitecture and can be used to evaluate the risk of osteoporotic fractures independently of bone mineral density (BMD). In this retrospective case-control study, we tested and compared the ability of TBS and lumbar spine BMD (LS-BMD) to predict vertebral fragility fractures. The inclusion criteria were female sex, age range 50-90 years, menopause, and clinical risk factors for osteoporosis. Patients with secondary osteoporosis were excluded. LS-BMD and TBS were measured at the L1-L4 vertebral level. The ability of the two diagnostic systems in predicting vertebral fragility fractures was assessed by combining LS-BMD and TBS according to the Bayesian "OR rule" (the diagnosis is negative only for those negative for both tests, and it is positive for those who were positive for at least one test) or to the "AND rule" (the diagnosis is positive only for those positive to both tests and is negative for those negative for at least one test). Of the 992 postmenopausal women included, 86 had a documented vertebral fragility fracture. At the cutoff value used in the present study, the TBS and LS-BMD showed a similar diagnostic ability to predict vertebral fragility fractures, having positive predictive values (PPV) of, respectively, 13.19% and 13.24%. Negative predictive values (NPV) were, respectively, 95.40% and 94.95%. Compared to that of each single diagnostic system, the "OR-rule" significantly increased the NPV to 97.89%, while no statistically significant differences were found by using the "AND-rule". In conclusion, the present study highlights the possibility that combining LS-BMD and TBS could improve their predictive ability in diagnosing vertebral fragility fractures, and that there is a significant probability of absence of fractures in women who test negative to both diagnostic systems.