Altered biomechanical strategies of the paretic hip and knee joints during a step-up task: a pilot study

Stroke often leads to chronic motor impairments in the paretic lower limb that can constrain lower extremity movement and negatively impact the ability to navigate stairs or curbs. This exploratory study investigated the differences in hip and knee biomechanical strategies during a step-up task between 5 adults with hemiparetic stroke and 5 age-matched adults without stroke. Participants were instructed to step up onto a 4-inch platform, where joint biomechanics were quantified for the hip in the frontal plane and the hip and knee in the sagittal plane. Peak joint kinematics were identified during the leading limb swing phase and peak joint moments and power were identified during the leading limb pull-up phase of stance. Mixed effects regression models estimated fixed effects of limb (3 levels: control dominant, stroke non-paretic, and stroke paretic) on biomechanical outcomes, while a random effect of participant controlled for within-participant correlations. Repeated assessments within participants (approximately 60 trials per lower limb) increased the effective sample size from 10 to between 12.0 to 19.6. Altered biomechanical strategies of the paretic lower limb included reduced flexion angles and increased pelvic obliquity angles during swing, decreased power generation in the hip frontal plane during stance, and decreased moment and power generation in the knee sagittal plane during stance. A strategy of substantial interest was the elevated hip sagittal plane moment and power generation in both stroke limbs. Overall, our findings suggest that chronic motor impairments from stroke can lead to inefficient biomechanical strategies when stepping up.