Dynamic Joint Stiffness of the Knee in Post-Menopausal Women with and without Rheumatoid Arthritis

Abstract

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 (R2). R2 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 (p < 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.