Who declines, who maintains? Trajectories of physical function and the role of social determinants of health in adults aging with physical disability

OBJECTIVES: This study sought to explore longitudinal trajectories of physical function in middle-aged and older adults living with long-term physical disability and to evaluate the impact of social determinants of health (SDOH) on physical function over time. METHODS: This study utilized 3 waves of an existing longitudinal survey on aging and disability, collected over a 2-year span. Participants were adults aged 45 and older with physical disability due to spinal cord injury, multiple sclerosis, muscular dystrophy, or post-polio syndrome. Physical function was assessed using the Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function measure. SDOH included health service availability, healthcare provider relationships, financial and physical barriers to healthcare, disability benefits, transportation access, community accessibility, and caregiving availability. Growth mixture modeling was employed to identify distinct physical function trajectory classes, and multinomial logistic regression was used to examine associations between SDOH and trajectory class membership. RESULTS: A total of 1,345 participants were included in the analysis. Four distinct physical function trajectory classes were identified: High-improving, High-declining, Moderate-declining, and Low-declining. Individuals in the Low-declining class were more likely to experience adverse SDOH, such as lower income, greater physical barriers to healthcare, and limited community accessibility. DISCUSSION: These results highlight the importance of unfavorable SDOH, particularly limited access to healthcare and community environments, in contributing to poorer physical health trajectories in people with disabilities. Inaccessible healthcare settings and community environments are not trivial inconveniences, but structural determinants that shape how people with disabilities age, suggesting that inclusive environments are foundational to achieving equity in aging.