Physical function in older people with rheumatoid arthritis and population controls: a cross-sectional study of self-reported and performance-based measures

To investigate whether the association between age and five measures of physical function differs between older adults with rheumatoid arthritis (RA) and population controls. This cross-sectional analysis of the STudying Ageing in Rheumatoid arthritis (STAR) study included 207 patients with RA and 214 population controls aged 55-85 years. Physical function was assessed by the self-reported Health Assessment Questionnaire-Disability Index (HAQ-DI) and Cochin hand function scale, and three performance measures including handgrip strength, gait speed and the five-times sit-to-stand test (FTSST) in a subgroup (RA: n = 88, controls: n = 108). Multivariable regression models assessed associations between age, group (RA/control), and each measure of physical function, adjusting for sociodemographic and clinical factors. Interactions age*group were tested. No meaningful age*group interactions were observed, except for a small effect on the FTSST. Age correlated weakly with measures of physical function in both groups and was, in multivariable analyses, only modestly associated with worse HAQ-DI (β = 0.01/year; 95%CI: 0.01-0.02), higher Cochin hand disability (worsening 2%/year), lower handgrip strength (β = -0.4 kg/year; 95%CI: -0.6 to -0.2), and a slightly slower gait speed (β = -0.01 m/s/year; 95%CI: -0.02 to -0.01). RA was independently associated with worse HAQ-DI (β = 0.12; 95%CI: 0.04-0.21), 40% higher Cochin scores, and lower handgrip strength (β=-3.2 kg; 95%CI:-6.1 to -0.4), but not with gait speed or FTSST. Fatigue and pain were the main covariables attenuating the association of age or group with physical function. Although older adults with RA experience worse self-reported physical function and lower grip strength, this was similar compared to population controls and suggests generic processes of ageing.