Mechanisms of Post-stroke Stiff-Knee Gait: A Narrative Review.

Stiff-Knee gait is a dysfunction commonly observed post-stroke characterized by a decreased swing phase knee flexion angle. Importantly, Stiff-Knee gait can impair walking, ultimately reducing overall activity and participation. Interventions for Stiff-Knee gait have shown mixed results and, combined with more recent observational evidence, suggest that there are other potential causes requiring the need to re-examine its etiology. The aim of this review is to compile and appraise the current state of the science regarding the neurophysiological and biomechanical impairments of individuals post-stroke with Stiff-Knee gait. This narrative review will address the following topics to better understand Stiff-Knee gait: operationally define Stiff-Knee gait and further detail its presentation, describe its potential neurophysiological and biomechanical mechanisms, and synthesize findings. We explore evidence for quadriceps hyperreflexia, abnormal tone, motor incoordination, and impaired propulsion. We conclude that Stiff-Knee gait needs a commonly accepted definition, that more attention needs to be devoted to understanding its mechanisms, and that in prospective designs, larger sample sizes are needed to account for the heterogeneity of the condition.