Shifting the focus in fracture prevention from osteoporosis to falls

Predictive value of bone density measurementsBone densitometry does not give reliable estimates of a person’s true bone mineral density. The planar scanning principle of dual energy x ray absorptiometry, and assumptions in processing the scan data, can underestimate or overestimate bone mineral density by 20-50%.8 This means that a patient with a bone mineral density T score of −1.5 may have a true value between −3.0 and 0−that is, a range from clear osteoporosis to normal. Thus, not surprisingly, bone mineral density is a poor predictor of fracture in individuals (fig 1⇓). In addition, when different scanners are used on the same patients, the proportion of patients diagnosed with osteoporosis varies from 6% up to 15%.9View larger version: In this window In a new window Fig 1 Femoral neck bone mineral density versus age at time of fall in people who did and did not sustain a hip fracture. Dashed lines show 2 SD less than peak bone mass for women (lower line) and men (upper line). Adapted from Greenspan et al Over 80% of low trauma fractures occur in people who do not have osteoporosis (defined as T score ≤−2.5).11 Even if a T score of −1.5 is used to define osteoporosis, 75% of fractures would still occur in people without osteoporosis.11 Thus, bone mineral density gives general practitioners little indication which patient will sustain a fracture. In addition, changes in bone density in people taking antiresorptive drugs explain only 4-30% of the reduction in risk of vertebral and non-vertebral fractures.12 The fracture index, a simple risk assessment tool based on clinical risk factors (age, previous fracture, mother’s hip fracture occurrence, weight, smoking, and ability to rise from a chair without hands) can predict fractures in postmenopausal women as well as bone mineral density.3 Adding bone mineral density to the index only marginally improves its ability to predict hip or other fractures (fig 2⇓).3 View larger version: In this window In a new window Fig 2 Five year incidence of hip fracture in postmenopausal women by score on fracture index (based on age, previous fracture, mother’s hip fracture occurrence, weight, smoking, and ability to rise from a chair without hands). The two panels illustrate the marginal effect of including bone mineral density on the ability of the index to predict future hip fractures. The finding was similar in other fractures. Adapted from Black et al