During the 26-year study period, 1980-2006, 2752 hip fractures occurred among Olmsted County residents (median age, 83 years; 76% female), excluding four isolated fractures of the greater or lesser trochanter. In accordance with the racial composition of the community (96% white in 1990), 97% of the patients were white. Altogether, 2441 (89%) represented a first-ever hip fracture, including 7 bilateral hip fractures, whereas the remaining 311 represented subsequent events. The overall age- and sex-adjusted (to 2000 U.S. whites) incidence of any hip fracture among Olmsted County residents during the study period was 119 per 100,000 person-years (95% CI, 114-123), including 105 per 100,000 person-years (95% CI, 101-110) for first-ever hip fractures and 13 per 100,000 person-years (95% CI, 12-15) for recurrent events. Incidence rates for all hip fractures and for first hip fractures alone are delineated in for the 5-year period, 1998-2002, the best compromise between recent fracture numerator data and accurate population denominator estimates anchored on the 2000 census.
Annual incidence per 100,000 of first-ever hip fractures and all hip fracture events observed among Olmsted County, Minnesota, residents in 1998-2002, by gender and age-group
However, fracture incidence rates for Rochester residents peaked for women in 1950 and for men in 1975 (). Between 1980 and 2006, first-ever hip fracture incidence in Rochester declined by 1.40%/year in women and was unchanged (0.04%/year) in men, while rates for rural Olmsted County residents fell by 1.26%/year in women and 0.79%/year in men. For Olmsted County as a whole, first fracture rates declined by 1.37%/year among women (p < 0.001) and 0.06%/year among men (p = 0.917) over this period. Comparable changes for all hip fractures since 1980 were -1.42%/year (p < 0.001) and -0.44%/year (p = 0.390) for women and men, respectively. These trends were the result of hip fractures precipitated by moderate trauma (by convention, the equivalent of a fall from standing height or less), which accounted for 86% of all fractures. The overall incidence (both sexes combined) of hip fractures due to severe trauma (e.g., motor vehicle accidents and falls from greater than standing height; 13% of the total) and specific pathological processes (e.g., metastatic malignancy; 1% of the total) changed only by -1.4%/year (p = 0.071) and 5.9%/year (p = 0.302), respectively, between 1980 and 2006.
Age-adjusted incidence (per 100,000 person-years) of first-ever hip fracture among women and men residing in Rochester (1928-2006) or rural Olmsted County (1980-2006), Minnesota, by calendar year.
There were 2434 patients with a first-ever hip fracture (1832 women and 602 men), of whom 219 (186 women and 33 men) experienced 222 recurrent hip fractures in over 10,000 person-years of follow-up (to death in 76% of cases). The average time between the first and second hip fracture was 3.9 years (median 2.7), 4.0 years (median 2.8) in women and 3.4 years (median 2.1) in men. The cumulative incidence of a subsequent one increased steadily by time after the first-ever hip fracture event and, after 20 years, was 29% (32% in women and 18% in men) when follow-up was censored at death (). At 10 years, the figure was 19% (20% in women and 12% in men). However, mortality was high in this population: After one year, 22% had died compared to an expected 9%, and analogous figures after 10 years were 80% and 63%, respectively (p<0.001). Relative survival (observed versus expected) was similar in men (53%) and women (56%) at the 10-year point, and there was no significant change in mortality over calendar time after adjusting for age and sex (p=0.237). also shows results with death taken into account as a competing risk. In this analysis, more reflective of what would actually be observed in practice, the estimated cumulative incidence of a recurrent hip fracture was only 10% at 10 years (11% in women and 6% in men) and 12% after 20 years (13% in women and 7% in men).
Cumulative incidence of a recurrent hip fracture among 2434 Olmsted County, Minnesota, women and men who had a first-ever hip fracture in 1980-2006, with follow-up censored at death or with deaths treated as a competing risk.
Compared to age, sex- and calendar year-specific first hip fracture rates for the population generally, the overall relative risk of a recurrent hip fracture among the 2434 with a first-ever hip fracture was 1.7 (95% CI, 1.5-2.0) and was similar for residents of urban Rochester (SIR, 1.7; 95% CI, 1.5-2.0) and rural Olmsted County (SIR, 1.7; 95% CI, 1.2-2.3). The influence of selected characteristics at baseline (time of the first-ever hip fracture) on recurrent hip fracture risk is delineated in . There it can be seen that the relative risk of another fracture, adjusting for the expected risk of fracture, was lowest in those with a first-ever hip fracture in 2000-2006 in contrast to earlier decades, although this trend was not statistically significant (p=0.080). In addition, recurrent hip fracture risk differed by age (p<0.001) and gender (p=0.011). There seemed to be little effect related to the etiology of the initial fracture (p=0.606), except for a trend toward increased risk in the small number with a pathologic hip fracture at baseline. Finally, the relative risk of a subsequent hip fracture, adjusting for expected hip fractures, seemed equivalent regardless of the type (femur neck, intertrochanteric) of first hip fracture (p=0.244) or the side that was affected (p=0.839). All results were similar when each patient’s individual hips were followed separately (data not shown).
Observed versus expected recurrent hip fractures and standardized incidence ratios (SIR, with 95% confidence interval) among 2434 Olmsted County, Minnesota, residents with a first-ever hip fracture in 1980-2006, by nature of the first hip fracture
However, this analysis obscures important information evident when the first-ever hip fracture type and side are considered together (). Thus, compared to site-specific Olmsted County first fracture rates, it is clear that patients with an initial femur neck fracture are at much greater relative risk of a recurrent femoral neck fracture in the opposite hip than they are of a contralateral intertrochanteric fracture or any recurrent fracture in the same hip. In part, the low risk of an ipsilateral fracture could have been due to the fact that 65% of patients with a first-ever femoral neck fracture had a hip arthroplasty at some point (90% within 3 months of fracture). However, when hips were followed separately and censored at arthroplasty, the result was similar, with an overall relative risk of recurrence in the same hip of just 0.6 (95% CI, 0.2-1.2). Likewise, the patients with an initial intertrochanteric hip fracture were at greatest risk of a recurrent contralateral intertrochanteric fracture (). They also were not at increased risk of any ipsilateral hip fracture recurrence. Only 14% of this group ever had a hip arthroplasty (60% within 3 months of fracture) but, again, when follow-up was censored at arthroplasty, the relative risk of a recurrent fracture in the same hip was only 0.2 (95% CI, 0.1-0.5). For all patients combined, the relative risk of a recurrent hip fracture in the same hip (censored at arthroplasty) was 0.3 (95% CI, 0.2-0.5), and in the opposite hip was 3.2 (95% CI, 2.8-3.7).
Observed versus expected recurrent hip fractures and standardized incidence ratios (SIR, with 95% confidence interval) among 2434 Olmsted County, Minnesota, residents with a first-ever hip fracture in 1980-2006, by hip fracture type and laterality
In a multivariate Andersen-Gill analysis, the only independent predictors of higher hip fracture recurrence were greater age (hazard ratio [HR] per 10-year increase, 1.5; 95% CI, 1.4-1.7) and more recent calendar year of the first-ever hip fracture, which was protective (HR per 10-year increase, 0.8; 95% CI, 0.6-0.9).
In order to determine if the trend to reduced hip fracture recurrence was related to the decline in hip fracture incidence generally, we described the temporal trend in hip fracture recurrence relative to expected hip fractures based on first-ever hip fracture incidence rates in the community (). While the relative risk of recurrence beyond expected seemed to decline after 1997, the overall downward trend did not achieve statistical significance in this analysis (p=0.105).
Observed compared to expected recurrent hip fractures over time among 2434 Olmsted County, Minnesota, residents with a first-ever hip fracture in 1980-2006. (Dotted lines indicate the 95% confidence interval.)