Effect of vertebral exclusion on TBS and FRAX calculations

Degenerative changes falsely elevate BMD; however, their impact on TBS is unclear. This study examined how spinal degenerative changes affect TBS-adjusted fracture risk (FRAX). In a majority, but not all patients in this sample, TBS decreased after exclusion of vertebrae with degenerative change. Therefore, vertebral exclusion for TBS is suggested.

Spinal degenerative changes elevate DXA-measured BMD, but reports find trabecular bone score (TBS) relatively unaffected. However, we observed patients where degenerative changes elevated both. Consequently, this study explored whether vertebral exclusion impacts TBS and subsequently TBS-adjusted FRAX risk.

Clinical DXA interpretations of one physician were reviewed; those with vertebrae excluded per ISCD guidance were included in this study. BMD and TBS at L1-4 and from post-exclusion vertebrae were collected and used to adjust fracture risk (FRAX).

Of the patients, 102 had vertebrae excluded; their mean (SD) age, BMI, and lowest T-score were 71.6 (9.5) years, 25.4 (4.5) kg/m², and - 2.8 (1.0), respectively. Compared to L1-4, vertebral exclusion lowered (p < 0.0001) mean spine BMD and TBS by 9.5 and 3.1%, respectively. Vertebral exclusion decreased TBS by 0.040, being lower in 83%. In those with lower TBS, the mean adjusted 10-year fracture risk increased (p < 0.0001) by 0.94 and 0.32% for major osteoporotic (MOF) and hip fracture, respectively, in some risk increased by up to 4%. In those with higher TBS, adjusted risk was reduced, MOF - 0.49% and hip - 0.1%.

Vertebral exclusion following ISCD recommendations generally, but not always, lowers TBS. Consequently, the impact on TBS adjusted FRAX risk is variable. In most patients, vertebral exclusion lowers TBS; in some, this could result in a relevant change in calculated fracture risk. It seems reasonable to use TBS values from evaluable vertebrae to adjust FRAX. Further research to determine if vertebral exclusion improves fracture risk prediction is needed.