A fall in the previous 12 months predicts fracture in the subsequent 5 years in postmenopausal women

Falls in the elderly are common [1] and result in fractures and other serious health consequences [2]. Among subjects aged 65 years or over, falls are the leading cause of injury-related death and hospitalization [3]. Thus, fall-induced injuries result in a substantial economic burden worldwide [4]. Research has shown a history of falls to be associated with a higher probability for future falls and risk of subsequent fractures [5‐9]. In cold climate countries, slipping is a common fall mechanism and results often in injuries (injurious falls) [10]. Thus far, longitudinal studies on how history of falls predicts future fractures have not been determined according to frequency, mechanism (slip/nonslip), or severity (injurious/non-injurious) of the fall [11‐13].

Previously, we have found that falling risks (especially nonslip falls) increased in women with multimorbidity (multiple chronic conditions) [14]. It is probable that due to effects of health disorders, women who have multiple nonslip falls are more unwell and less physically active compared with women with slip falls [15]. Falling events resulting in injury also reflect the overall health condition of the individuals [16]. The aim of the present study was to determine if an overall history of falls (frequency, mechanism, and severity) or its parts are useful predictors of future fracture in postmenopausal women.

The present study shows that a history of falls (especially injurious falls) is an important risk factor for future fracture, in particular for other fractures compared to major osteoporotic fractures among postmenopausal women. To our knowledge, fracture risk (major osteoporotic vs other) according to mechanism (slip/nonslip) and severity (injurious/non-injurious) of previous falls has not been previously examined in a prospective cohort study.

In the present study, the annual fall incidence rate (20%) was less than previously reported (30%) in studies including elderly women aged 65 years or over [1]. The mean age [62.2 years (range 57–66)] of the included study population likely explains the lower incidence rate, as rate of falls increases with increasing age [5, 20]. Slipping was the most common falling mechanism and the proportion of slip falls was clearly higher than in most studies conducted in warmer climates [21]. The long and icy winter season in the cold climate countries leads to frequent outdoor slip falls, which explains their higher occurrence compared to nonslip falls in the present study population [22].The self-reported use of estrogen hormone therapy was higher among women with no fracture and has a significant preventive effect on future fractures. This observation is in alignment with our previous studies from the OSTPRE follow-up [19, 23]. Although, we previously found that the use of estrogen therapy appeared to have a preventive effect on falls in early but not in late menopausal women [24]. It is possible that the effects of hormone therapy on fall risk reduce with age.

By understanding how frequency, mechanism, and severity of previous falls modify the risk of future fractures (major osteoporotic vs other), specific measures for fracture prevention can be developed accordingly [13, 25‐27]. In the present study, we found higher future fracture risk due to previous slip falls (OR = 1.43) compared with previous nonslip falls (OR = 1.35). However, there was no statistically significant difference between the two (slip vs nonslip) risk predictions (Table 2). A plausible explanation for the observed increase in fracture risk prediction due to slip falls could be that women who have had previous slip falls are more physically active and capable of moving outdoors more often than women with a previous history of nonslip falls. These women would have greater exposure to slippery conditions which is a known risk factor for fracture [14, 15].

We observed that previous slip and nonslip falls were associated with other fractures but not major osteoporotic fractures. In addition, the risk of other fractures was considerably greater in relation to previous (injurious) falls. The greater other fractures risk related to previous history of falls (frequency, mechanism, and severity) could indicate that these women are healthier; they may have stronger bones and less risk factors for major osteoporotic fractures. In addition, for individuals considered frail or falls out of the ordinary caused by an unavoidable external cause (such as traffic accident or slipping outside), fracture may be inevitable and, in this sense, the fall per se may not have any significant role on such fractures.

To shed more light on these findings, we analyzed the associations between history of falls (frequency, mechanism, and severity) and site-specific fractures. According to the point estimates, previous falls (especially injurious falls) tended to increase the risk of future fractures of each of the specific sites, in particular the other fractures. However, the associations were often not statistically significant; the relatively small numbers of individual fracture types likely limited the power to detect statistical differences. Adjustment for mobility could have further clarified the findings and remains an idea for further exploration. Also, the classification of fractures into major osteoporotic vs others is not necessarily justified, since the risk for all types of fracture is increased in women with osteoporosis.

Finally, our finding, suggesting that earlier injurious falls is a strong predictor for future fracture especially for other fractures compared with major osteoporotic fractures, could be a good candidate for inclusion in fracture prediction algorithms. The current FRAX (fracture risk prediction model) screening tool includes falls; however, the inclusion of previous injurious falls in particular is likely to improve predictive power [28].

The main strength of our study was its prospective population-based design and the large study population with an overall high response rate. Some limitations are also evident. There may be possible recall biases as falls are based on self-reports [29]. In addition, we classify the mechanism of fall based on the last falling event which might affect future fracture risk estimates. Therefore, further fracture risk studies with more exact fall reporting methods and detailed information on fall mechanism would have needed to confirm the results. In the current study, the self-reported fractures were confirmed via medical reports. The former validation study of self-reported fractures in OSTPRE cohort observed the sensitivity of self-report to detect fracture to be 78% and specificity 96% [30]. So, it is true that some fractures may have been missed, but when a fracture was reported, it had a positive predictive value of 84% truly to be a fracture. Thus, we can assume that there was no severe recall bias involved in the self-reported fracture rates. Even further, there is no reason to believe that self-reporting would have been systematically different between the compared groups meaning that relative risks remain unbiased even though we certainly have lost some power to detect differences and therefore the study results are likely to be rather conservative. This study includes those women who responded to the fall and fracture questionnaires. The incidence of future fractures in non-responders to fall questions was same as in responders suggesting that the fracture risks related to fall history were similar in responders and non-responders. Thus, non-response to fall questions has not severely affected the future fracture risk estimations. Non-response to fracture questions is not biasing our comparisons, but generalizations beyond the population capable of answering the questionnaires should not be made without careful justifications. The current study used the major osteoporotic fracture site criteria established by FRAX and was not aiming to separate fractures due to true status of osteoporosis or trauma energy. This approach was chosen to make our finding more comparable with other similar studies using the same classification criteria. To verify osteoporotic fracture, we would have ultimately needed BMD values, but unfortunately timely BMD measurements were available only for a small fraction of this population-based cohort and detection for truly osteoporotic fractures was impossible. In order to classify women into categories of major osteoporotic and other fractures, we considered any women who had reported at least one fracture in sites of major osteoporotic fractures to belong in major osteoporotic category and women with solely other fractures to belong in other category. So, our approach allowed us to report site-specific fracture risks in a consistent and comparable way. But as it is certainly possible that some women may have more than one fracture event, we recognize that it would be interesting to focus on that aspect in future research but that is out of scope of the current study.

In conclusion, history of falls (especially injurious falls) appeared to be an indicator for subsequent postmenopausal fracture overall. Earlier injurious falls are a stronger predictor for other fractures than for typical major osteoporotic fractures. Early identification of those at a greater risk for future fracture is the key to minimizing the associated health burden. With this knowledge, clinicians could identify those at a greater fracture risk. These findings are relevant in improving screening and prevention strategies for fractures.