85 How to identify fallers and non-fallers in people with HSP Introduction Hereditary spastic paraplegia (HSP) comprises a heterogenous group of neurodegenerative disorders. Pure forms of HSP are clinically characterized by progressive bilateral spasticity, muscle weakness, and loss of proprioception of the lower extremities. 1 Due to these symptoms, balance and gait impairments are common, disabling and often result in fear-of-falling, falls, and fall-related injuries. 2, 3 In order to optimally tailor fall prevention interventions, the clinical field is in need of measures that can identify individuals with HSP who exhibit a propensity for falling, and those who do not. Nonetheless, this is a relatively unexplored topic in HSP. Fall risk can be assessed using different constructs: balance confidence is used to assess perception of fall risk through patient-reported outcomes (e.g., the Activitiesspecific Balance Confidence scale (ABC)) 4, 5, whereas objective clinical measures are used to assess general balance capacity (e.g., Mini Balance Evaluations Systems Test (Mini-BEST)) 4, 6 or gait capacity (e.g., self-selected gait speed during the ten-meter walk test) 7. Moreover, biomechanical measures of gait stability (e.g., spatiotemporal gait variability, mediolateral Margin of Stability (MoS), mediolateral Foot Placements Deviation (FPD), and Local Divergence Exponents (LDEs)) can objectify detailed aspects of dynamic balance capacity. 8 The ability of these measures to differentiate between fallers and non-fallers has been reported in various neurological populations. 9-14 Even though the aforementioned studies offer important insights, their potential to discriminate between fallers and non-fallers in people with HSP has not been evaluated. In this study, we evaluated the potential of both clinical and biomechanical balance and gait measures for the fall risk assessment in ambulatory people with pure HSP. To this end, we assessed the different constructs, i.e., subjective balance confidence, objective clinical balance and gait capacity, and biomechanical measures of gait stability. As a first explorative step, we evaluated whether these constructs differed between people with pure HSP and healthy age-matched controls. Second, we divided the HSP cohort into fallers and non-fallers based on their real-life fall incidence and assessed the ability of these constructs to discriminate between fallers and non-fallers among people with HSP. Methods Participants and setting This study was part of the data collection in a randomized clinical trial. 15, 16 Specifically, we obtained fall rates logged by the participants in the fifteen weeks prior to the first assessment. Thirty-three of the 36 participants with pure HSP (age: 48.7±11 years, 73% male) were included in the current study: three participants were excluded 6
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