Biomechanical effects of a semi-rigid knee orthotic during walking in individuals with medial knee osteoarthritis

Background: Medial knee osteoarthritis is associated with increased medial compartment loading during gait.
Valgus unloader knee orthotics are commonly used to reduce medial knee loading, but the biomechanical re-
sponses associated with semi-rigid designs remain unclear.
Research question: After six weeks of use, what effect does the orthotic condition have on first-peak knee
adduction moment (KAM), second-peak KAM, and knee adduction angular impulse (KAAI) during constant-speed
and self-selected-speed walking compared with baseline in individuals with medial knee osteoarthritis?
Methods: Twenty-four participants with Kellgren-Lawrence grade 2–4 completed a within-participant pretest-
–posttest study. Gait was assessed without the orthotic at baseline and while wearing it after six weeks of use
(mean 5.13 h/day), at a constant speed of 1.39 m/s and self-selected speed. In OpenSim, first-peak KAM, second-
peak KAM, and KAAI were calculated. GRF variables were secondary, exploratory outcomes. Conditions were
compared using paired t-tests or Wilcoxon signed-rank tests. Holm-Bonferroni adjustment was applied to the
three KAM-related outcomes within each walking condition.
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Results: During constant-speed walking, first-peak KAM, second-peak KAM, and KAAI were lower with the or-
thotic by 6.9% , (r = 0.44), 6.8% (r = 0.47), and 15.8% (r = 0.51), respectively (Holm-adjusted p = 0.045 for
each). Vertical GRF variables did not differ, whereas the braking-peak magnitude and braking and propulsive
impulses increased. During self-selected-speed, participants walked 15.5% faster in the orthotic condition
(p < 0.001). First- and second-peak KAM did not differ significantly from baseline, whereas KAAI was lower
( 0.030 N⋅m⋅kg⁻¹⋅s, 95% CI 0.050 to 0.010; Holm-adjusted p = 0.014). The first vertical, braking, and
propulsive GRF peaks increased, while vertical impulse decreased.
Significance: Semi-rigid orthotic use was associated with lower KAM-related loading during constant-speed
walking and faster self-selected walking without higher peak KAM. The semi-rigid orthotic may be considered
a possible adjunct to individualized, multicomponent care for individuals with medial knee osteoarthritis.