| Summary: | This study compared rheumatoid arthritis (RA) post-menopausal women with pathological involvement of the lower limb joints and age-matched post-menopausal women without RA regarding the dynamic joint stiffness (DJS) of knee during the stance phase of gait. Eighteen RA women and eighteen age-matched women were selected. Gait assessed through a three-dimensional motion analysis system synchronized with a force plate. Subjects walked barefoot at self-selected speed, and 14 valid trials were collected (comprising 7 left and 7 right foot-steps on force plate). The “moment of force—angle” plot of knee in sagittal plane was determined. The stance phase was split into three sub-phases: first knee flexion sub-phase (1st KFS); knee extension sub-phase (KES); second knee flexion sub-phase (2nd KFS). A linear model represented each sub-phase and DJS calculated by the slope. Model fitting was assessed through the coefficient of determination (R<sup>2</sup>). R<sup>2</sup> values for both groups were higher than 0.8 during 1st KFS and KES but not during 2nd KFS. RA women yielded a higher DJS value during 2nd KFS (<i>p</i> < 0.01). Concerning the other sub-phases, no differences were observed between groups. The findings suggested the splitting methodology used could be modelled by a linear “moment of force—angle” relationship, namely, during 1st KFS and KES. During 2nd KFS, RA women yielded a stiffer behavior.
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