Mortality risk doubles during the year after hip fracture among women aged 65 years and older, then returns to baseline in many women; but this pattern doesn’t apply in all cases, according to a report published online Sept. 26 in Archives of Internal Medicine.

Mortality risk after sustaining a hip fracture differs by patient age, underlying health, and the interval since the injury occurred in this population, said Dr. Erin S. LeBlanc of the center for health research at Kaiser Permanente Northwest Region, Portland, Ore., and her associates.

Previous studies of this issue have had methodological limitations and have yielded inconsistent results. Most have shown increased short-term mortality, but have had mixed findings on long-term mortality. "Our data suggest that previous mixed results ... may have been the result of differences in the underlying age and health status of the population being studied," Dr. LeBlanc and her colleagues said (Arch. Intern. Med. 2011 Sept. 26 [doi:10.1001/archinternmed.2011.447]).

They used data from the SOF (Study of Osteoporotic Fractures) to address these methodological limitations. The subjects were identified before hip fractures occurred, the study design was prospective, and extensive data on comorbidities allowed adjustment for potentially confounding factors.

The SOF subjects were 5,580 community-dwelling women aged 65 and older who resided in Maryland, Minnesota, Oregon, and Pennsylvania at baseline in 1986-1988. This population included 1,116 women who sustained incident hip fractures during a mean follow-up of 14 years, and 4,464 age-matched control subjects without hip fracture.

Mortality risk was highest in the first year after hip fracture. The rate was 16.9% among cases, compared with only 8.4% among controls. This doubling of risk persisted when the analysis was adjusted to account for factors such as total hip bone mineral density.

Moreover, deaths in the control group were evenly spread throughout the year, whereas those in the case group were concentrated within the first 6 months of the year. "In addition, more than half the deaths (99 of 189 [52.4%]) in the first year following hip fracture occurred within the first 3 months for the cases," the investigators said.

When the study subjects were categorized by age (younger than 70 years, 70-79 years, or 80 years and older), the youngest group showed a fivefold rise in mortality risk during the first year after hip fracture (16.3%), compared with women younger than 70 who did not sustain a hip fracture (3.7%).

In contrast, the oldest women showed no increased mortality risk in the year following hip fracture, and the women in the middle group showed an intermediate risk.

In addition, mortality risk remained elevated for years 1-10 among women in the youngest age group, but it was somewhat lower than the mortality risk in the first year. In contrast, mortality risk declined to baseline for the next 10 years among women in the two older age groups.

"We hypothesize that age influences the risk of death after hip fracture by affecting the baseline death rate in the population. Those who are younger ... have a low risk of dying from other causes. Therefore, experiencing a hip fracture may increase their mortality risk compared with nonfracture controls.