A greater knee adduction moment increases risk of medial tibiofemoral OA progression. Greater toe-out during gait shifts the ground reaction force vector closer to knee center, reducing the adduction moment. We tested whether greater toe-out is associated with lower likelihood of medial OA progression.
Baseline assessments included: kinematic/kinetic gait parameters using an optoelectronic camera system, force platform, and inverse dynamics to calculate 3-D external knee moments; toe-out angle (formed by line connecting heel strike and toe-off plantar surface centers of pressure and forward progression line; knee pain; full-limb alignment. Knee x-rays (semi-flexed) were obtained, baseline and 18 months, with progression as medial joint space grade worsening. With logistic regression, ORs for progression/5%X toe-out were estimated.
In the 56 (59% women, mean age 66.6, BMI 29), baseline toe-out angle was less in knees with than without progression [difference -4.4, 95% CI (-8.5, - 0.3)]. Greater toe-out was associated with reduced likelihood of progression [OR 0.60, 95% CI (0.37, 0.98)]. Adjusting for age, gender, BMI, pain severity, disease severity, OR was 0.62, 95% CI (0.36, 1.06). Adjusting for adduction moment (second peak), OR was 0.72, 95% CI (0.40, 1.28).
OA knees that progressed had less toeing-out than knees without progression. Greater toe-out was associated with a lower likelihood of progression. Adjustment for covariates did not alter the OR, although the 95% CI included 1. Further adjustment for adduction moment did alter the OR, consistent with the possibility that a mechanism of the effect may be via lowering of the adduction moment.