Impact of spine-hip discordance on fracture risk assessment and treatment qualification in Canada: the Manitoba BMD registry

In 50,330 women undergoing bone mineral density (BMD) testing, adjusting FRAX® major osteoporotic fracture (MOF) probability for T-score differences between lumbar spine and femoral neck had a small impact on treatment qualification, with only 1.1% reclassified from below to above the 20% MOF intervention threshold.

Purpose: Discordance between lumbar spine and femoral neck T-score measurements are frequently encountered in clinical practice. The FRAX tool accepts femoral neck BMD as an optional input but does not consider lumbar spine BMD, though adjustments based upon T-score difference have been proposed. This analysis was undertaken to examine change in treatment qualification using the lumbar spine T-score adjustment to FRAX assuming an intervention threshold of 20% MOF.

Methods: Women aged > 50 years with baseline FRAX MOF probability computed with femoral neck BMD of ≥ 20% but without previous high-risk fracture or high-risk medication use were identified in the province of Manitoba BMD registry. If lumbar spine T-score was lower than the femoral neck T-score, MOF probability was recalculated, and treatment qualification, reassessed.

Results: The study population consisted of 50,300 women (mean age 64.2 ± 8.6 years). During mean follow-up of 9.5 years, 4550 sustained incident MOF. The baseline mean T-score difference (femoral neck minus lumbar spine) was - 0.2 ± 1.1. Recalculated MOF probability using the T-score difference significantly improved overall net reclassification index for incident MOF prediction (+ 0.017, p < 0.001). A total of 561 (1.1%) of these women were reclassified from below to above 20% MOF probability based upon the T-score difference. No individuals with MOF probability less than 15% were reclassified to the higher risk category. Risk reclassification increased with lower lumbar spine T-score (15.6% reclassification for lumbar spine T-score of - 3.5 or lower, 4.0% of the study population) and larger T-score differences (9.7% reclassification for T-score difference of 2.5 or more, < 1% of the study population).

Conclusions: Very few women showed risk reclassification based upon adjusting FRAX MOF probability for lumbar spine T-score. Reclassification occurred only in those with baseline MOF probability > 15%.