JPM | Free Full-Text | The “Can Do, Do Do” Framework Applied to Assess the Association between Physical Capacity, Physical Activity and Prospective Falls, Subsequent Fractures, and Mortality in Patients Visiting the Fracture Liaison Service

The global burden of disease of fractures is high. About 50% of females and 20% of males are estimated to sustain a fracture after their 50th life year [1]. In the European Union, the number of fragility fractures alone (e.g., fractures due to osteoporosis) was estimated to be 4.3 million in 2019, resulting in a total cost of EUR 56.9 billion, and it is expected to rise in the future [2]. Fractures are associated with short- and long-term disability and a decrease in quality of life [2]. Fracture patients have a high imminent risk of falls, subsequent fractures, and mortality [3]. Therefore, adequate and early secondary fall and fracture prevention is essential to lower the risk of subsequent falls, fractures, and mortality post-fracture [4,5]. The Fracture Liaison Service (FLS) is the recommended organizational approach for fracture prevention in terms of (cost-)effectiveness [6,7,8]. At the FLS, personal risk factors are evaluated, including causes of osteoporosis, comorbidities, and medication use. FLS care ideally includes a fall assessment [4].

In FLS patients, approximately 80% of subsequent fractures are fall-related [9]. The majority of falls in older persons occur during mobility tasks, such as walking, and most falls are caused by slips and trips [10,11]. An evaluation of physical performance including mobility tasks is therefore an essential part of fall risk evaluation [12]. The “can do, do do” framework is a recent approach for an integrated assessment of physical performance. It combines two distinct, yet related, domains of physical performance: physical capacity (PC; can do, can’t do) and physical activity (PA; do, do, don’t do) into four quadrant groups [13,14]. PC is objectively measured physical performance; in the “can do, do do” framework, the 6 min walking test (6MWT) is used to test walking ability [13,15]. Impaired walking ability (e.g., abnormalities in gait or balance) has been associated with future falls [12,16,17,18,19] and fractures and post-fracture mortality (in males) [20,21]. PA is defined as “any bodily movement produced by skeletal muscles that results in energy expenditure”, and is measured by an accelerometer [13,22]. PA might protect or expose (due to higher exposure to risk) persons to falls [23,24,25,26]. In fact, some studies found a U-shaped association with both inactive and highly active adults at increased fall risk [26]. The “can do, do do” framework has proven to be a useful and practical tool to identify patient subgroups with distinct clinical characteristics [13,15,27,28]. In patients with COPD, a preserved PC was found to be associated with a lower 6-year mortality risk compared to decreased PC, regardless of PA level [29]. A recent study in patients with a fracture showed that the framework was able to categorize patient groups in terms of fall and fracture risk factors, such as fall history, fear of falling, type of fracture, and osteoporosis [15].

A previous cross-sectional assessment of the “can do, do do” framework showed differences in fall and fracture risk factors between the quadrant groups; patients in the can’t do, don’t do” group were older; presented with more major index fractures; more often had osteoporosis, prevalent vertebral fractures, and comorbidities; scored lower on all physical performance tests; and more often used a walking aid [15]. Contrarily, our study did not show an association with the clinically relevant outcomes of first fall (at three years), first fracture, and mortality (at six years). Our results are also in contrast with studies in the general older population associating poor physical performance (including both PC and PA measures) with future falls [12,25], subsequent fractures [42,43,44], and mortality [39,45,46,47,48]. Studies in fracture populations are fewer in number, but several involving older individuals with hip, radius, or any low-trauma fracture have reported associations between poor PC (using balance and gait measures) and falls [49,50,51,52] and post-fracture mortality in older males [52]. Poor PA has been associated with subsequent fractures in older males [53,54], but not females [55], after fracture. Interestingly, one study reported that males with a recent fracture who sustained a subsequent fracture had higher PA and gait speed measures compared to those who did not sustain a subsequent fracture [52]. This suggests that they may be more likely to engage in risky behavior. However, comparability between the studies in fracture patients is low, as they differ in terms of the age and sex of the included population, index fracture type, timing of the measurement before or after fracture, and measurement method of PC (different performance tests were evaluated) and PA (mostly self-reported with questionnaire) [52,54]. Only one study previously explored the “can do, do do” framework prospectively. Vaes et al. explored mortality risk in the different quadrant groups in patients with COPD [29] and found that patients with preserved PC had significantly lower 6-year mortality risk than those with poor PC (HR = 0.36, 95% CI; 0.14–0.93). In our study, PC (can do vs. can’t do) was associated with mortality in the univariate but not multivariate analysis. However, in the study by Vaes et al. the threshold values were study population driven and not based on pre-determined cutoff scores for poor or normal PC and PA. The lack of association with mortality outcomes in our study might be explained by the low mortality incidence during follow-up. The survival of 95.5% was the same as the 6-year survival of 65-year-olds in the general Dutch population (95.8%) [56], indicating a healthy subset of fracture patients, who generally have an increased mortality risk [3].

The absence of associations in our study might also be attributed to the unequal distribution of participants in the framework that resulted in a small number of participants included in the “can do, don’t do” and “can’t do, don’t do” groups. This was partly due to the low proportion of patients with low PA. The use of predefined cutoff scores for poor and normal PA (39,57]. These are in line with other cutoff scores: 58]; and in community-dwelling older males, those with a history of >2 falls had an average of 24 min MVPA/day compared to 40 min/day in non-fallers [59]. In our study, the assessment of composite endpoints using the quartile distribution (instead of predefined cutoff scores) did not show superior discrimination between groups. Thus, the chosen cutoff scores do not seem to have had a great influence on the absence of an association.

More likely, our study population is too homogeneous, as it consists primarily of individuals who have sustained a fracture and are nearly all “previous fallers”. In 86.5% of our study population, the fracture that led to FLS evaluation was caused by a fall, and this did not vary between quadrant groups. Patients with a recent fracture are at a high risk for subsequent falls and fractures, with 38% of our participants experiencing a fall in the first year and 60% in the first three years, and 21% sustaining a subsequent fracture during six years of follow-up, despite evaluation and treatment according to best practice standards. These incidences did not differ between quadrant groups. Therefore, our study suggests that measures of PC and PA, measured during the FLS visit, do not differentiate enough between patients with a recent fracture to show any association with the clinical outcomes of falls, fractures, and mortality—a conclusion that was also suggested in a previous study assessing physical performance and subsequent fracture risk [52].

To effectively evaluate the likelihood of future fractures, it is crucial to assess fall risk factors, as falls are a significant predictor. A comprehensive review of the World Falls Guidelines emphasized the multifactorial nature of fall prediction and concluded that no single measurement can guarantee a high level of confidence in fall risk assessment for older adults. The review recommended both balance and gait assessments in fall prediction [12,17]. They further underlined that mobility assessment is only one part of fall prediction, and many other factors (e.g., fall-risk-increasing drugs, cardiovascular management, and cognitive function and sensory function decline) are also important [12]. Consequently, fall prediction and prevention is highly personalized. Interventions, including physical performance interventions, need to target multiple domains and need to be tailored to the patients’ needs [12,60,61]. Our study underlines this; even though the “can do, don’t do” framework offers a more complex approach compared to single physical function tests, this framework remains on one hand too “simplistic” to capture the multifactorial causes of falls and fractures. On the other hand, in testing and constructing combined measures, we lose information for a tailor-made, individual evaluation of different physical performance domains and corresponding treatment options. Thus, the categorization into a two-dimensional framework is inadequate to study complex clinical outcomes such as falls, fractures, and death, and a personalized approach based on existing fall and fracture risk factors from international guidelines [4,12] seems preferable.