Impact of FRAXplus adjustments vs FRAX on fracture risk classification in the Swiss Osteoporosis Registry

FRAXplus complements the fracture risk assessment tool (FRAX) by incorporating additional risk factors to adjust 10-yr probabilities of major osteoporotic and hip fractures. We aimed to identify which adjustments most strongly influence fracture risk estimates and how they affect risk classification and treatment recommendations in Switzerland. We analyzed data from the Swiss Osteoporosis Registry (2015-2023), which captures all standard FRAX variables plus lumbar spine (LS) BMD, trabecular bone score (TBS), fall history in the previous year, oral glucocorticoid dosages, and the location and recency of prior fractures. Data on hip axis length and duration of type 2 diabetes were not available. A total of 28 708 individuals (88% women; mean age 65.8 ± 11.4 yr) were included, with a median 10-yr probabilities for major osteoporotic fracture (MOF) of 16% (interquartile range [IQR]: 9-24) using standard FRAX and 18% [IQR: 11-28] with FRAXplus adjustments. Most individuals (72%) had higher probabilities with FRAXplus (mean absolute increase: +4.8%), while 27% had lower probabilities (mean absolute decrease: -1.0%). TBS and LS minus FN T-score (LS - FN) influenced nearly all risk estimates, but differences between FRAX and FRAXplus were generally modest. At the individual level, ≥1 fall and recent vertebral or hip fractures produced the largest differences. Applying FRAXplus with Swiss intervention thresholds led to an upward reclassification in 16% of MOF estimates and a downward reclassification in 1%. In summary, FRAXplus adjustments significantly alter fracture risk estimates for most individuals. While LS BMD and TBS affect most probabilities, falls and recent vertebral or hip fractures have the largest absolute impact at the individual level, leading to clinically relevant changes in treatment recommendations according to Swiss guidelines.