To determine the effects of modifying stride length (SL) on knee adduction and flexion moments, two markers of knee loading associated with medial-compartment knee osteoarthritis progression. This study also tested if SL modifications, in addition to foot progression angle (FP) and step width (SW) modifications, provide solutions in more subjects for reducing knee adduction moment without increasing knee flexion moment (potentially protecting the joint).
Fourteen healthy subjects (6 female) were enrolled in this preliminary study. Walking trials were collected first without instructions, and then following foot placement instructions for 50 combinations of SL, FP, and SW modifications. Repeated measures analysis of variance was used to detect group-average effects of footprint modifications on maximum knee adduction and flexion moments and on knee adduction moment impulse. Subject-specific dose-responses between footprint modifications and kinetics changes were modeled with linear regressions, and the models were used to identify modification solutions, per subject, for various kinetics change conditions.
Shorter SL significantly decreased the three kinetics measures (p<0.01). Potential solutions for 10% reductions in knee adduction moment maximum and impulse without increasing maximum knee flexion moment were identified for 5 subjects with FP and SW modifications. A significantly higher proportion of subjects had solutions when adding SL modifications (11 subjects, p=0.04).
SL is a valuable parameter to modify, especially in combination with FP and SW modifications, to reduce markers of medial knee loading. Future work is needed to extend these findings to osteoarthritic knees.

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