Abstract
Background: People with knee osteoarthritis stand and walk with increased trunk flexion. This altered postural alignment increases hamstring activation, elevating mechanical knee loads during walking. Increased hip flexor stiffness may lead to increased trunk flexion. Therefore, this study compared hip flexor stiffness between healthy individuals and indi-viduals with knee osteoarthritis. This study also sought to understand the biomechanical effect of a simple instruction to reduce trunk flexion by 5 degrees during walking.Methods: Twenty individuals with confirmed knee osteoarthritis and 20 healthy individu-als participated. The Thomas test was used to quantity passive stiffness of the hip flexor muscles and three-dimensional motion analysis used to quantify trunk flexion during nor-mal walking. Using a controlled biofeedback protocol, each participant was then instructed to decrease trunk flexion by 5 degrees.Results: Passive stiffness was greater in the group with knee osteoarthritis (effect size = 1.04). For both groups, there was relatively strong correlation between passive stiff-ness and trunk flexion in walking (r = 0.61-0.72). The instruction to decrease trunk flexion produced only small, non-significant, reductions in hamstring activation during early stance.Conclusions: This is the first study to demonstrate that individuals with knee osteoarthritis exhibit increased passive stiffness of the hip muscles. This increased stiffness appears to be linked to increased trunk flexion and may therefore underlie the increased hamstring acti-vation which is associated with this disease. As simple postural instruction does not appear to reduce hamstring activity, interventions may be required which can improve postural alignment by reducing passive stiffness of the hip muscles.(c) 2023 Published by Elsevier B.V.