Background/Purpose: Biomechanical factors including excessive knee loading have been shown to be important in the pathophysiology, severity and progression of knee osteoarthritis (OA).  Several biomechanical interventions reduce knee loads by altering foot mechanics, and there is a great deal of interest in better understanding mechanical relationships between the foot and knee.  We have previously shown that barefoot walking in OA is associated with a significant reduction in knee loading compared to conventional footwear.  Here we evaluate the role of foot center of pressure (COP) in predicting the unloading response of the knee when walking barefoot. 

Methods: Participants with radiographic (KL grades ≥ 2) and symptomatic (at least 30mm pain of 100mm scale while walking) medial compartment knee OA underwent gait analyses with their own shoes and while walking barefoot.  For simultaneous COP and 3-D ground reaction force acquisition, a pressure platform (Emed, Novel, Munich, Germany) was mounted onto a force plate (Bertec, Columbus, OH) and the stacked assembly was leveled with the walkway. All capture systems were run at 100 Hz to allow for accurate syncing of stance phase, knee moments, and plantar pressures.  Foot COP was quantified by determining a custom Medial to Lateral Pressure Index (MLPI) while barefoot. The peak knee adduction moment (KAM) was evaluated as a surrogate of medial knee loading.  Linear regression was used to evaluate the relationship between foot COP and percent reductions in the KAM with walking barefoot compared to own shoes.  The relationships between foot COP and other gait parameters and OA severity were also evaluated.

Results: 22 participants (15 women, mean age (SD) of 62±11) were evaluated. 10 had a KL grade of 2 and 12 had a KL grade of 3 at the affected knee.  Barefoot walking was associated with a 15% reduction in the KAM compared to walking with participants own shoes (2.55±1.00 vs 2.17±1.01%BW*ht, p<0.001); notably, the magnitude of reduction of the KAM with barefoot walking was associated with a more medial foot COP after adjusting for speed and stride length (adjusted r²=0.509, p=0.049).  A medialized foot COP was associated with worse KL grade, slower walking speed and shorter strides during gait (r²=0.564, p=0.002).   Radiographic severity explained 9 to 26% of the variance in the foot COP while speed and stride length explained 17 to 47%.  

Conclusion: Foot mechanics are important contributors to knee loading in OA.  There is controversy in the literature regarding the foot COP and how it may relate to various foot-targeted interventions in OA. This study suggests that a more medial foot COP is associated with greater reductions in the KAM during barefoot walking.  Thus, foot COP may help predict knee loading responses to walking barefoot or an intervention that simulates barefoot walking.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/foot-center-of-pressure-in-knee-osteoarthritis-oa-and-its-association-with-knee-load-reduction-with-barefoot-walking/