ASSOCIATION BETWEEN FOOT PROGRESSION ANGLE AND KNEE ADDUCTION MOMENT IN OSTEOARTHRITIS: A CROSS-SECTIONAL STUDY USING TWO ANALYTICAL TECHNIQUES

Abstract

Determine the association between net external knee adduction moment (KAM) characteristics and foot progression angle (FPA) in asymptomatic individuals and those with moderate and severe osteoarthritis through discrete variable and principal component analysis (PCA).

Fifty-nine asymptomatic (age 52 ± 10 years), fifty-five with moderate knee OA (age 60 ± 9 years) and sixty-one individuals with severe knee OA (age 67 ± 8 years, tested within one week of total knee replacement surgery) participated. Three-dimensional (3D) motion (Optotrak) and ground reaction force (AMTI) data were recorded during gait. Subjects walked at a self-selected velocity. The KAM, calculated using inverse dynamics was time normalised to one complete gait cycle. FPA was calculated using stance phase kinematic gait variables. The discrete variable, peak KAM, was extracted for the interval (30–60%) of the gait cycle. PCA was used to extract the predominant waveform features (Principal Components (PC)) of which PC-Scores were computed for each original waveform. Pearson Product Moment Correlations were calculated for the FPA and both the PC-scores and peak KAM. Alpha of 0.05 used to test significance.

No significant correlations were noted for the groups between peak KAM and the FPA, or for the first PC-Scores (PC1) of which captured the original KAM waveforms overall magnitude and shape. The second PC (PC2) captured the shape and magnitude during the second interval of stance (30–60%) with respect to the first. Correlations of FPA to PC2 were significant for the asymptomatic group(r=−0.40, p=0.002) and the moderate OA group (r=−0.32, p=0.017) but not for the severe group(r=−0.13, p=0.316).

No relationship between FPA and peak KAM was found across the groups using discrete variable analysis despite reports of associations in asymptomatic subjects. The PCA results suggest a toe out FPA was moderately correlated to a decreased KAM during 30–60% of the gait cycle for asymptomatic and moderate OA individuals only. These individuals respond to a toe out progression angle, altering the KAM which directly affects medial knee compartment loading, where those with severe OA do not.