Objective: To determine the causes of hip or wrist fractures.
Design: Case-control analysis nested in a prospective cohort study.
Setting: Four clinical centers in Baltimore, Maryland, Minneapolis, Minnesota, Portland, Oregon, and Monessen, Pennsylvania.
Participants: Non-black women age 65 and older living in the community.
Measurements: We measured bone density, arm strength, and anthropometric characteristics at a baseline examination. Those who subsequently suffered hip (n = 130) or wrist (n = 294) fractures as a result of a fall and a consecutive sample of those who fell without a fracture (n = 467) were interviewed about their falls.
Results: In multivariate analyses, those who suffered hip fractures were more likely to have fallen sideways or straight down (odds ratio 3.3; 95% confidence interval 2.0 to 5.6) and to have landed on or near the hip (32.5; 9.9, 107.1) than women who fell without a fracture. Among women who fell on the hip, those with hip fractures were taller (1.5; 1.2, 2.2 per SD increase), less likely to have landed on a hand (0.3; 0.1 to 0.6) or to break the fall by grabbing or hitting an object (0.4; 0.2, 0.9), had weaker triceps (1.7; 1.2, 2.5 per SD decrease), and were more likely to land on a hard surface (2.8; 1.4, 5.5) than those without fractures. Women with wrist fractures were more likely to have fallen backward (2.2; 1.3, 3.8) and to have landed on a hand (20.4; 11.5, 36.0) than those who fell without a fracture. Among women who fell on the hand, those with wrist fractures were taller (1.4; 1.1, 1.8 per SD increase) and less likely to break the fall by grabbing or hitting an object (0.4; 0.2, 0.7). Among women who fell on their hip or hand, the risk of fracturing that site more than doubled for each standard deviation decrease in bone density at the site of fracture.
Conclusions: The nature of the fall determines the type of fracture, while bone density and factors that increase or attenuate the force of impact of the fall determine whether a fracture will occur when a faller lands on a particular bone. These findings have important implications for prevention of fractures in older women.