Introduction

Globally, falls have become an increasing challenge for the aging population, resulting in a greater risk of hospitalization, loss of independence and mortality (1, 2). With advancing age, the incidence of falls and their negative outcomes are expected to increase. Fear of falling (FOF) is also common among older adults, which may cause fear-related activity restriction (FAR) and result in deficient activity engagement and declined physical function (3). Falls and FOF are closely related and are usually associated with similar factors, which negatively affect the health of older adults (4, 5). Fall-related outcomes imposed a significant burden on older adults. The average cost of a medically treated fall was estimated to be $9780, and fatal and nonfatal fall costs were estimated to be $50 billion in 2015 in the United States (6, 7). Therefore, it is of great importance to identify risk factors for fall-related outcomes among older adults.

Mobility devices, such as canes and walkers can help older adults to improve physical stabilization, reduce the load on the lower limbs and maintain independence (8). Older adults with falls and FOF often use mobility devices to compensate for mobility limitations and prevent fall-related injuries. Although mobility devices are beneficial for fall prevention in older adults, research suggested that mobility device use was associated with a greater risk of falls and FOF (9–12). The use of a walker was found to be associated with recurrent falls (13). Additionally, a longitudinal study of 7,609 participants concluded that the incidence of falls and recurrent falls were not related to the use of mobility devices, but FAR was significantly higher among cane-only users compared with non-users (14). Evidence was still insufficient regarding the causal impacts of mobility device use on fall-related outcomes. To effectively apply mobility devices among older adults, it is imperative to further investigate the association between mobility device use and fall-related outcomes.

Frailty, a reversible geriatric syndrome commonly seen in older adults, is considered a predictor of future falls and FOF (15, 16). Older adults with frailty reported a high prevalence of mobility difficulties and often use mobility devices to deal with difficulties with mobility or daily activities (17). Given the dynamic reversible nature of frailty, it is reasonable to speculate that the relationship between mobility device use and fall-related outcomes may differ during the transition processes of frailty (i.e. improve or worsen). A previous study has shown that frail older adults who used ambulatory assistive devices reported more falls than non-users (18). In addition, assistive device use at the time of a fall was significantly associated with worry about re-injury and limiting one’s activities due to this worry, but this association became insignificant after controlling for frailty variables, indicating that frailty should be considered when determining the relationship between mobility device use and falls (19). However, to our knowledge, little is known about the association between mobility device use and fall-related outcomes according to different frailty statuses (robust, prefrail and frail). Given the challenges of fall-related outcomes and frailty in older adults, investigating the associations between mobility device use and fall-related outcomes by frailty status is necessary to provide appropriate prescriptions for mobility devices and establish effective strategies for fall-related management for the older population.

Therefore, this study aimed to evaluate the longitudinal relationships of mobility device use, falls and FOF according to frailty status by examining 1) whether the number of mobility devices used at Year 1 predicted falls and FOF at Year 2 among robust, pre-frail and frail older adults; and 2) whether the use of canes at Year 1 predicted falls and FOF at Year 2 among robust, pre-frail and frail older adults. We hypothesized that 1) the number of mobility devices used at Year 1 independently predicted falls and FOF at Year 2 after adjusting for falls/FOF, demographics and health-related covariates at Year 1 among robust, pre-frail and frail older adults; and 2) the use of canes at Year 1 independently predicted falls and FOF at Year 2 after adjusting for falls/FOF and other covariates at Year 1 among robust, pre-frail and frail older adults.

Methods

Study sample

We used data from Year 1 (2011) and Year 2 (2012) of the National Health Aging Trends Study (NHATS), a nationally representative longitudinal cohort study of U.S. Medicare beneficiaries aged 65 or older. The data collection has been conducted through in-person interviews since 2011 and then tracked annually to examine the disability trends of older adults in late life (20). In this study, we included a total of 5,896 community-dwelling participants who provided complete data on falls, FOF and FAR, frailty and mobility device use. The blinded for peer review approved the protocol. All participants or their proxy respondents provided written informed consent.

Measures

Assessment of fall-related outcomes

Falls were defined as any fall, slip, or trip in which one loses balance and lands on the floor or ground or at a lower level. Participants were asked whether they had a fall and if they fell more than once in the last 12 months (yes or no). Falls were categorized into 3 groups (no fall, one fall, and recurrent falls).

FOF was assessed by asking participants if they worried about falling in the last month (yes or no). Participants were then asked whether this worry ever limited their activities based on the “yes” response to the previous question. FOF was classified into 3 groups (no FOF, FOF without FAR, and FOF with FAR).

Assessment of mobility device use

Mobility device use was measured by asking participants whether they used any mobility device use in the last month, including the use of a cane, walker, wheelchair (manual, power, electric, or motorized), and/or scooter (yes or no). Categories of mobility device use were created based on the number of devices used in the last month into 3 groups (no device, 1 device, and ≥2 devices). Considering that canes are easy to carry and inexpensive to afford for older adults with mobility and balance problems, participants were additionally classified into 2 groups (cane-only users and non-device users).

Assessment of frailty status

Frailty was assessed by NHATS interview and performance assessments using the physical frailty phenotype paradigm based on 5 criteria: unintentional weight loss, exhaustion, weakness, slow gait and low physical activity (21). Unintentional weight loss was defined as unintentionally losing 10 pounds or more in the last year. Exhaustion was identified as self-reported low energy or being easily exhausted to limit activities. Weakness was assessed by maximum grip strength measured by the dominant hand over 2 trials as being at or below the 20th percentile. Slow gait was determined as gait speed from the best of two timed 3-meter walk tests being at or below the 20th percentile. Low physical activity was defined as self-reported not having taken part in vigorous activities or never walking for exercise in the last month. Participants were grouped into 3 types: those meeting 3 or more criteria were classified as “frail”, 1–2 as “pre-frail”, and none as “robust.

Covariates

Demographic variables included chronological age, gender (female, and male), education (less than high school, high school graduates, some college or vocational school, and bachelor or higher), race/ethnicity (non-Hispanic White, non-Hispanic Black, Indian/Asian/Native/Hawaii, Hispanic, and other) and living arrangement (alone, with spouse/partner only, with others only, with spouse/partner, and with others).

Health-related variables included the following: (1) the number of activities of daily living (ADL) impairments regarding eating, dressing, bathing and toileting; (2) the number of chronic diseases (heart attack, heart disease, high blood pressure, arthritis, osteoporosis, diabetes, lung disease, stroke, cancer) diagnosed by a doctor; (3) dementia or Alzheimer’s disease diagnosed by a doctor; (4) BMI classified into 2 groups (normal with BMI <30 kg/m2, and obesity with a BMI ≥30 kg/m2); (5) depression assessed by the Patient Health Questionnaire (PHQ-2) scale; (6) bothersome pain in the last month; (7) reported hospitalization in the past year; (8) vigorous activities that increased heart rate and made breathing harder in the last month.

Data analysis

Descriptive statistics for demographics, health-related factors and mobility device use are presented with frequencies, percentages, means and standard deviations (SDs). Chi-square test and one-way analysis of variance (ANOVA) were used to assess the differences among groups of participants by frailty status. Multinomial logistic regressions were conducted to evaluate the associations of mobility device use, falls and FOF according to frailty status, with independent variables of interest examined in Model 1 and further adjustments for covariates including demographic and health-related variables in Model 2. The association between mobility device use and falls was examined among participants with no falls at Year 1. The association between mobility device use and FOF was investigated among participants with no FOF at Year 1. To improve the robustness of our results, we excluded the data from proxy respondents to perform sensitivity analyses. Since the missing values on covariate variables were less than 1.0 %, we did not use any techniques to handle the missing data. P value of less than 0.05 was considered to be statistically significant. All statistical analyses were conducted using STATA 15.

Results

In this study, a total of 5,896 community-dwelling older adults were included. The average age of participants was 77.4 years old. Of all the participants, about 58.2% participants were female and 69.6% were non-Hispanic whites. The proportion of robust, pre-frail and frail respondents was 35.9%, 48.7% and 15.4%, respectively. The use of mobility devices varied according to frailty status. The percentage of using at least 1 mobility device was largest among frail participants (69.5%), followed by pre-frail (30.5%) and robust (8.4%) participants. The most used mobility device was a cane and the least used was a scooter, regardless of the frailty status (Table 1).

Table 1 Baseline characteristics of participants stratified by frailty status (N=5,896)
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The number of mobility devices used predicting falls and FOF by frailty status

Table 2 shows the multinomial logistic regression results examining the relationship between the number of mobility devices used at Year 1 and fall-related outcomes at Year 2 according to frailty status. For falls, among robust respondents, the number of mobility devices used was not significantly associated with one fall or recurrent falls. Among pre-frail respondents, using ≥2 mobility devices was significantly related to one fall (RRR=2.08, 95% CI: 1.30–3.33) after adjusting for demographic and health-related covariates. In addition, pre-frailty individuals who used one mobility device and used ≥2 mobility devices were more likely to have recurrent falls (RRR=2.02, 95% CI: 1.30–3.14; RRR=2.92, 95% CI: 1.62–5.25) compared with those without using any mobility devices. The number of mobility devices used was not significantly associated with falls among frail participants.

Table 2 The number of mobility device used at Year 1 predicting fall-related outcomes at Year 2 by frailty status
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For FOF, regardless of the frailty status, the associations were not significant between the number of mobility devices used and FOF without FAR in the adjusted models. For robust individuals, using 1 mobility device was associated with FOF with FAR after controlling for all covariates (RRR=3.58, 95% CI: 1.10–11.65), while using ≥2 mobility devices was not. For pre-frail individuals, those who used one mobility device (RRR=2.13, 95% CI: 1.25–3.63) and used ≥2 mobility devices (RRR=2.84, 95% CI: 1.34–6.02) had a higher risk of having FOF with FAR compared with non-device users. No significant association was observed between the number of devices used and FOF with FAR among frail participants.

Cane use predicting falls and FOF by frailty status

Table 3 shows the results of the association between the use of a cane at Year 1 and fall-related outcomes at Year 2 according to frailty status. For falls, there exists no significant results in the fully adjusted models concerning the association between the only use of a cane and falls among robust and frail participants compared with those who did not use any mobility devices. However, in pre-frail participants, cane-only users had a higher risk of having one fall (RRR=1.57, 95% CI: 1.06–2.32) and recurrent falls (RRR=2.36, 95% CI: 1.48–3.77) rather than non-device users.

Table 3 Cane use at Year 1 predicting fall-related outcomes at Year 2 by frailty status
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For FOF, robust older adults who were cane-only users were 2.18 times and 5.94 times more likely to have FOF without FAR (95% CI: 1.12–4.22) and FOF with FAR (95% CI: 1.80–19.57) than non-device users. Among pre-frail participants, cane-only users were 2.08 times more likely to have FOF with FAR (95% CI: 1.12–3.87) compared with non-device users. No significant association was found between cane use and FOF among frail participants.

Sensitivity analyses excluding proxy respondents supported the robustness of the current findings assessing the association between mobility device use and fall-related outcomes among robust, pre-frail and frail participants (see supplementary material table 1 and table 2).

Discussion

Using a nationally representative sample of community-dwelling older adults, the study examined the longitudinal relationship between mobility device use, falls and FOF by frailty status. We found that frail older adults accounted for the largest percentage of the use of mobility devices. Canes were the most used devices in each frailty group. The adjusted models showed that for robust older adults, using one mobility device was significantly associated with FOF with FAR. For pre-frail older adults, those using ≥2 mobility devices were more likely to have one fall, and those using at least one mobility device had higher risks of recurrent falls and FOF with FAR compared with non-device users. Additionally, robust cane-only users were more likely to have FOF with and without FAR. Pre-frail cane-only users had higher risks of having one fall, recurrent falls as well as FOF with FAR than non-device users.

In this study, the number of mobility devices used was not associated with falls in robust older adults. However, robust participants who used one mobility device had increased risks of developing FOF with FAR compared with non-device users. Besides, robust participants who used only canes had higher odds of having FOF with and without FAR. Possible reasons may explain these results. On one hand, older adults identified as robust were generally younger and had better physical functions than those with pre-frailty or frailty, which contributed to fewer mobility problems and lower falls rate (22, 23). Besides, the limited sample size of robust mobility users may account for insufficient statistical power to identify the longitudinal association between mobility device use and falls for robust older adults. On the other hand, mobility device use among robust participants may be associated with numbers of potential factors. For example, as older adults age, they may gradually perceive a decline in physical function and become worried about falling down (24).

We found that the number of mobility devices used and the only use of canes were significantly associated with falls and FOF among pre-frail participants. Compared with robust older adults, pre-frail older adults may have worse health conditions at Year 1 and experienced fall-related injuries in the past years that contribute to their impaired physical function, falls and FOF at Year 2. However, pre-frail older adults may not have mobility disabilities that require the use of mobility devices to assist with physical activities. Given that the risk factors of falls are complicated and interacted with each other, potential reasons causing fall-related outcomes among pre-frail older adults may be other factors (e.g. chronic diseases) apart from the use of mobility devices, which cannot be determined in the present study (25). In addition, though pre-frail individuals possessed mobility devices for safety reasons to prevent fall-related outcomes, they may use mobility devices inappropriately which ultimately lead to fall-related outcomes. For example, mobility device users may not be using the devices when falling down even if they acknowledged the importance of using mobility devices to prevent falls. Others may incorrectly use the mobility devices (e.g. wrong hand, wrong size, never taught by a physical therapist) which possibly leads to fall-related outcomes (18, 25).

Contrary to the study hypothesis, frail mobility device users seemed not to have greater risks of falls or FOF than nondevice users. It is acknowledged that mobility device is of great importance for fall prevention among older adults. Therefore, the insignificant relationship between mobility device use and fall-related outcomes among frail participants may confirm the effectiveness of mobility devices, indicating that mobility device use can be effective in preventing falls and FOF. However, from another perspective, frail older adults tend to have very little physical activity, and are often sedentary, which limits the risk of falls and FOF by itself (27). Furthermore, the insignificant association may also be explained by the relatively small sample size of frail participants in this study, resulting in inadequate statistical power. Though mobility device use was not significantly associated with falls or FOF among frail older adults in the present study, as one of the most vulnerable populations, great efforts are needed for the development of tailored fall prevention. Frailty is a dynamic process that involves transitions between frailty statuses over time. It is suggested that there were more transitions to greater frailty than to lesser frailty (28). Identification of mobility device use in older adults with frailty is of great significance to inform the development of fall prevention. Studying the relationship between changes in frailty status and the use of assistive devices will also be useful in providing insights for the design of fall prevention programs and ultimately enhance the quality of life for older adults.

Although the current study demonstrated the longitudinal relationship between mobility device use, falls and FOF among older adults by frailty status, the findings of this study need to be viewed with caution. Many factors, including the physical and psychological characteristics of the mobility device users, the assessments and prescriptions of the appropriate mobility devices, the environmental demands and other potential factors may directly or indirectly affect the effectiveness of the mobility device use in preventing falls and FOF. For example, beliefs and attitudes toward mobility device use are vital for fall prevention. It is suggested that most mobility device users fell when they were not using it, even if they believed in the effects of devices to prevent falls (18, 29). Social pressures and perceived stigma could also lead to reduced acceptance or even abandonment of mobility devices (30, 31). Further research may benefit from examining more detailed information on mobility device use to deepen understanding of its relationship with fall-related outcomes among older adults with and without frailty.

Strengths and limitations

To our knowledge, this is the first study to determine the longitudinal relationship between mobility device use, falls and FOF by frailty status based on a nationally representative sample. The longitudinal nature of the study allows us to examine if mobility device use contributes to falls and FOF among older adults according to frailty status. However, several limitations should be acknowledged. Firstly, the study was limited by retrospective self-reports of the main variables and therefore subject to recall bias and potential underreporting. Older adults tend to underreport falls and fall injuries (32). Monthly calendars are recommended to collect fall-related data. Additionally, mobility device use was classified according to the use of cane, walker, wheelchair and scooter. However, given the different applications and characteristics of the mobility devices in different contexts, these four types of devices cannot be generalized as the same, which should be investigated in future research. Lastly, additional information including the cause, frequency and duration of the mobility device use was not identified in the study, which should be addressed in future research to provide insights into fall prevention for high-risk older adults.

Conclusions

In summary, the number of mobility devices used and the only use of canes were significantly associated with falls and FOF among robust and pre-frail older adults. Healthcare professionals should pay special attention to multiple-device users and cane-only users among older adults in the early stage of frailty. Besides, targeted preventive interventions should be developed and implemented to prevent and reduce the risk of fall-related outcomes.