Contribution of Lumbar Spine BMD to Fracture Risk in Individuals With T‐Score Discordance

ABSTRACT Fracture risk estimates are usually based on femoral neck (FN) BMD. It is unclear how to address T‐score discordance, where lumbar spine (LS) T‐score is lower than FN T‐score. The objective of this work was to examine the impact of LS BMD on fracture risk, in individuals with lower LS T‐score than FN T‐score. Participants aged 60+ years from the Dubbo Osteoporosis Epidemiology Study with LS and FN BMD measured at first visit, and were followed from 1989 to 2014. Five‐hundred and seventy‐three (573) of 2270 women and 131 of 1373 men had lower LS than FN T‐score by ≥0.6 standard deviation (SD) (low‐LS group based on least significant change). In low‐LS women, each 1 SD lower LS T‐score than FN was associated with a 30% increase in fracture risk (hazard ratio [HR] 1.30; 95% CI, 1.11 to 1.45). For low‐LS men there was a 20% nonsignificant increase in fracture risk for each 1 SD lower LS than FN T‐score (HR 1.20; 95% CI, 0.10 to 1.67). Low‐LS women had greater absolute fracture risks than the rest of the women. This increased risk was more apparent for lower levels of FN T‐score and in older age groups. At an FN T‐score of –2, low‐LS women had a 3%, 10%, and 23% higher 5‐year absolute fracture risk than non‐low LS women in the 60 to 69 year, 70 to 79 year, and 80+ years age‐groups, respectively. Furthermore, an osteoporotic LS T‐score increased 5‐year absolute fracture risk for women with normal or osteopenic FN T‐score by 10% to 13%. Men in the low‐LS group had very few fractures; therefore, a meaningful analyses of fracture risk could not be conducted. This study shows the significant contribution of lower LS BMD to fracture risk over and above FN BMD in women. A LS BMD lower than FN BMD should be incorporated into fracture risk calculators at least for women in older age‐groups. © 2015 American Society for Bone and Mineral Research.