Variations in situational risk factors for fractures of the distal forearm, hip, and vertebrae in older women

Falls are a leading cause of injury and death in older adults. Approximately 5% ~ 10% of falls lead to major injuries such as fractures [1], and 90% of all fractures among people aged ≥65 years occur as a result of falls [2, 3]. Women are 50% more likely to have a fall injury and 75% more likely to have a lifetime fracture risk, compared to men [4, 5].

Although individual characteristics, such as age-related changes, a female gender, comorbidities, medications, and low bone mineral density (BMD), have been identified as risk factors for fractures [6], most of these individual characteristics are not modifiable or reliable for predicting fracture risks [1, 7]. On the other hand, situational factors during falls (e.g., circumstances and biomechanics of falls) were found to determine the type and severity of injury [8], and hence, identifying situational risk factors may help focus preventive efforts on falls with higher risks of fractures.

Among older women, the most common fractures are of the distal forearm, hip, and vertebrae [9]. While distal-forearm fractures occur most frequently as a result of a fall on an outstretched hand in healthy and active women with lower BMD [10], few studies have investigated the influence of situational exposures on the risk of other types of fracture, in which conflicting results exist as to whether a distal-forearm fracture is more likely to occur when falling backwards, sideways, or forwards [11‐13]. A hip fracture is considered to be the most devastating consequence of falling in older people [14], and the risk of hip fractures may increase six-fold when falling sideways compared to falling backwards/forwards [15]. The vertebral body is the most common site of fractures, and an existing radiographic vertebral fracture also signals an increased risk of subsequent vertebral fractures and hip fractures [16, 17]. Nonetheless, no study has reported situational risk factors for vertebral fractures, although these factors could explain why most clinical vertebral fractures do not occur in older patients with a diagnosis of osteoporosis [18]. Comparisons of the relative impacts of situational factors on various types of fractures can provide information to more comprehensively describe risk profiles for the three types of fracture and for developing more-precise prevention programs for older people with various risks of a certain type of fracture.

Accordingly, a case-control study was conducted to investigate the effects of situational factors, in addition to individual characteristics, on the most common fractures of the distal forearm, hip, and vertebrae among older women in Taiwan.

Of 1888 eligible women during the study period, 1484 agreed to participate in the study, among whom 203 had sustained a distal forearm fracture, 189 had sustained a vertebral fracture, 375 had sustained a hip fracture, 717 had sustained a soft-tissue injury, and 404 declined to participate or had no relatives or caregivers around to serve as proxies. Proxy respondents were obtained on behalf of 82 patients with a fracture and 39 patients with a soft-tissue injury. Participation rates of older women with distal-forearm fractures, hip fractures, vertebral fractures, and soft-tissue injuries were 83.1, 80.1,75.0, and 77.5%, respectively, and no significant differences in age (75.8 vs. 75.9 years; p = 0.960) or injury type (p = 0.102) between participants and non-participants were detected.

Distributions of sociodemographics and lifestyles, medical characteristics, and functional abilities among the four groups of distal-forearm fracture, hip fracture, vertebral fracture, and soft-tissue injury are shown in Table 1. Among the four groups, significant differences were found in the age at injury, educational level, living arrangement, BMI, regular alcohol consumption, regular exercise, BMD, fall history in the past year, presence of previous fractures since the age of 50 years, number of chronic conditions, medication use, use of sedatives/hypnotics and antidiabetics, visual acuity, use of walking aids, cognitive impairment, depressive symptoms, and fear of falling.

Distributions of situational factors in the three fracture groups and controls are shown in Table 2. Among the four groups, significant differences were detected in the location, mode and direction of the fall, the presence of an uneven floor, and hitting an object and initiating a protective response during the fall. Among these groups, distal-forearm fractures tended to have occurred more frequently during outdoor activities, tripping, and falling forward, and with an uneven floor. Vertebral fractures tended to have occurred more frequently during a step-down, when falling backwards, and with a stable COM. Hip fractures tended to have occurred more frequently during outdoor activities, when leg-weakness occurred, when stepping-down, falling in a sideways direction, and in the absence of a protective response.

Table 3 shows results of the multivariable multinomial logistic regression analysis for distal-forearm fractures, hip fractures, and vertebral fractures compared to soft-tissue injuries. After adjusting for individual characteristics (age, educational level, living arrangement, BMI, BMD, and number of chronic conditions), compared to soft-tissue injuries, distal-forearm fractures were significantly more likely to occur in slips (OR = 11.0; 95% CI = 4.76 ~ 25.4), trips (OR = 3.40; 95% CI = 1.42 ~ 8.17), step-downs (OR = 4.95; 95% CI = 2.15 ~ 11.4) and from sideways falls (OR = 1.73; 95% CI = 1.12 ~ 2.67) and significantly less likely to occur in indoor activities (OR = 0.62; 95% CI = 0.42 ~ 0.90) or from backwards falls (OR = 0.62; 95% CI = 0.41 ~ 0.95). Hip fractures were significantly more likely to occur in step-downs (OR = 1.76; 95% CI = 1.13 ~ 2.75) and from backwards (OR = 3.16; 95% CI = 2.15 ~ 4.64) and sideways falls (OR = 5.56; 95% CI = 3.67 ~ 8.41) and significantly less likely to when hitting an object (OR = 0.26; 95% CI = 0.13 ~ 0.52) or initiating a protective response (OR = 0.58; 95% CI = 0.36 ~ 0.93) during the fall. Vertebral fractures were significantly more likely to occur in slips (OR = 2.42; 95% CI = 1.30 ~ 4.50) and step-downs (OR = 2.53; 95% CI = 1.43 ~ 4.48) and from backwards falls (OR = 2.15; 95% CI = 1.39 ~ 3.32). For model checking, p values of the Hosmer-Lemeshow test ranged from 0.569 to 0.912, indicating no significant differences between observed and predicted values.

Table 4 shows the validation results of the binary logistic regression analyses separately for distal-forearm fractures, hip fractures, and vertebral fractures. With few exceptions (i.e., sideways falls for distal-forearm fractures, step-downs for hip fractures, and slipping for vertebral fractures), most of associations between situational factors and each type of fracture compared to the other two types of fracture, despite being weakened to some extent, were similar to results when soft-tissue injuries were used as the control group. For instance, the adjusted OR of falling backwards changed to 0.46 (95% CI = 0.30 ~ 0.69) for distal-forearm fractures, 2.75 (95% CI = 1.79 ~ 3.97) for hip fractures, and 1.70 (95% CI = 1.12 ~ 2.57) for vertebral fractures.

Previous studies reported that initial distal forearm or vertebral fractures were associated with subsequent fractures of the vertebrae, hip, distal forearm, and other sites, and risks of different fracture types resulted from similar individual characteristics such as an older age and low BMD [16, 17, 25, 26]. This study compared the relative impacts of situational factors during a fall on the three common types of fracture in older women, while controlling for individual characteristics. As a result, large variations in situational risk factors, such as location, mode, and direction of falls, existed among the three fracture types of the distal forearm, vertebrae, and hip in older women.

In contrast to distal-forearm fractures associated with falls in the forward and sideways directions in the study, two studies of older women reported that distal-forearm fractures were more likely to have occurred when they fell backwards or sideways, compared to those with no fracture [11, 12]. One explanation for the differences might be that fall modes that were not evaluated in the two studies could have confounded their findings, since slipping falls are usually concomitant with a backward fall direction. Alternatively, our participants who had lower BMIs than subjects in those two studies (mean BMI: 19.5 vs. 26.0 and 25.9 kg/m²) may have had increased chances to walk with a faster gait speed, thereby providing more opportunities to have a forward loss of balance; overweight and obese older people tend to walk at a slower speed and exhibit poorer functional fitness and mobility compared to those of a normal weight [27, 28]. Furthermore, stepping-down falls in our study were associated with increased risks of all the three types of fractures. It is possible that as the body COM descends to a lower level, failure to transform higher potential energy and control the relevant momentum causes a higher-impact fall with a more-serious injury, particularly during unexpected height changes (e.g., from a street curb or an uneven floor, into a hole, or during stair descent) [29].

Consistent with previous studies [8, 13, 30, 31], hip fractures were strongly associated with falling sideways. Some researchers suggested that people may execute backward rotation during a fall to impact the buttocks or execute forward rotation to impact the outstretched hands to avoid an impact to the hip with an initial sideways fall direction [32]. However, converting a sideways fall into a backwards one should be done with caution because falling backwards has also been linked with the incidence and severity of traumatic brain injuries [33, 34]; moreover, falling backwards also increases the risks of hip and vertebral fractures. Safer landing strategies based on falling directions to reduce fall severity and prevent serious injuries were recently explored in detail [35]. In addition to the fall direction, consequences of falls might also depend on the velocity and force of impact and the protective reaction time [36]. A low-impact sideways fall might result in a minor injury or a wrist fracture, whereas a fast, high-impact sideways fall might result in a hip fracture, particularly for frail older persons who may have too-late compensatory reactions (e.g., stepping and grasping) in response to a loss of balance [37]. Older women not only have lower BMDs but also less effectively provide arm protection reactions in preventing falling to the ground compared to older men [13, 38]. It should also be noted that sufficient muscle strength of the extremities is essential for successfully conducting safe landing strategies and effective compensatory reactions. The association of hitting an object during a fall with hip fractures might reflect competing risks of non-hip injuries and hip fractures during a fall, where, for instance, hitting the arms or hands first might lead to an injury to the forearm but prevent a direct impact to the hip [39].

Although individual characteristics of age and BMD were often reported as strong personal risk factors for older women [40], probably because women have lower vertebral strength and greater declines in strength over time compared to men [41], one-half of all clinical vertebral fractures occur in persons without a diagnosis of osteoporosis [42]. In this study, vertebral fractures occurred most frequently in a backwards direction and the step-down mode, while backwards and step-down falls also exhibited higher risks of vertebral fractures compared to other directions or modes. It is difficult to make comparisons with prior studies because no study has provided situational factors during falls resulting in vertebral fractures, even though some biomechanical studies simulated backward falls to evaluate impact forces on the lumbosacral spine [43].

There are several limitations to this study. First, our participants might not be representative of a population-based sample for the three types of fractures and soft-tissue injuries. Almost all of the new distal-forearm and hip fractures were identified in the ED, while in contrast, a portion of vertebral fractures and soft-tissue injuries might not have been serious or painful enough for an older person to have sought ED services. Nevertheless, our validation analyses in which patients who sustained the other two types of fracture were used as the comparison group produced similar results. Second, the results cannot be generalized to all older fallers, particularly those who are mentally and physically dependent, because not all older fallers come to the ED and some were excluded from the study due to severe cognitive impairment, non-ambulation, or being medically incapacitated. Third, self-reported data on situational factors were difficult to validate, even though our method of immediate assessment at the ED may have reduced memory lapses and recall errors related to time factors to some degree. Differential memory lapses and recall errors between older subjects and proxy respondents might also exist. Fourth, several medications related to risks of falls and fractures (e.g., antipsychotics, antidepressants, antiepileptics, anti-Parkinson drugs, opioids, and proton pump inhibitors) that might have confounded the results were not measured or assessed in the study. Finally, the impact velocity and force which affect the fall severity were not measured, and their distributions might not be the same among the three fracture types.

Despite the benefits of primary fall-prevention programs (e.g., multifactorial interventions and exercise training), individuals who participate in these programs still fall. Our study demonstrated that large variations in situational risk factors, such as location, mode, and direction of the fall, may exist among fractures of the distal forearm, hip, and vertebrae in older women. A combination of personal and situational risk factors may display a more-comprehensive risk profile for each type of fracture, and an intervention that adds training programs on fall safety, such as safe landing strategies and effective compensatory reactions, can be valuable in preventing serious injuries due to a fall.