Population-based analysis of the relationship of whole bone strength indices and fall-related loads to age- and sex-specific patterns of hip and wrist fractures.
In an age- and sex-stratified population sample (n = 700), we estimated fall-related loads and bone strength indices at the UDR and FN. These load/strength ratios more closely simulated patterns of wrist and hip fractures occurring in the same population than did measurement of vBMD.


BACKGROUND
Areal BMD measurements, although associated with fracture risk, incompletely explain patterns of fragility fractures. Moreover, population-based assessments relating applied loads and whole bone strength to fracture patterns have not been made.


METHODS
Using QCT, we assessed volumetric BMD (vBMD), cross-sectional geometry, and axial (EA) and flexural (EI) rigidities (indices of bone's resistance to compressive and bending loads, respectively) at the ultradistal radius (UDR) and femoral neck (FN) and estimated the loads applied to the wrist and hip during a fall. We used fall load (FL)/bone strength ratios to estimate fracture risk.


RESULTS
vBMD in young adults was similar between sexes. Decreases in vBMD over life were also similar (30% and 28%) at UDR but were somewhat greater (46% and 34%) at FN in women versus men, respectively. In young adults, FL/strength ratios at UDR were 32-51% lower (better) in men than in women and increased (worsened) over life less in men (+4% to +22%) than in women (+20% to +33%). In young adults, FL/strength ratios at FN were only marginally better in men than in women but worsened less over life in men (+22% to +36%) than in women (+40% to +62%).


CONCLUSIONS
The 6:1 female preponderance and the virtual immunity of men for age-related increases in wrist fractures are largely explained by the more favorable FL/strength ratios at UDR in young adult men (because of larger bone size and more favorable geometry) versus women and to maintaining this advantage over life. The 2-fold lower incidence of hip fractures in men versus women is largely explained by age-related increases (worsening) of FL/bone strength ratios that are only one-half of the increases in women. The moderate increases in these ratios with aging are insufficient to explain the >4-fold increase in hip fracture incidence after age 75 in both sexes, suggesting contributions of other factors, especially the well-documented increased frequency of injurious falls among the elderly.
Riggs
B Lawrence
BL
Endocrine Research Unit, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA. Riggs.Lawrence@Mayo.edu
Melton
L Joseph
LJ
Robb
Richard A
RA
Camp
Jon J
JJ
Atkinson
Elizabeth J
EJ
Oberg
Ann L
AL
Rouleau
Peggy A
PA
McCollough
Cynthia H
CH
Khosla
Sundeep
S
Bouxsein
Mary L
ML
D015502:Absorptiometry, Photon; D000058:Accidental Falls; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D005260:Female; D005265:Femoral Neck Fractures / Q000453:epidemiology*; D006615:Hip / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006620:Hip Fractures / Q000000981:diagnostic imaging / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011884:Radius / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011885:Radius Fractures / Q000000981:diagnostic imaging / Q000453:epidemiology*; D012737:Sex Factors; D016474:Weight-Bearing