Background/Purpose: The peak external knee adduction moment (KAM) as measured through gait analyses has been associated with severity, progression and pain in medial knee osteoarthritis (OA); thus, biomechanical approaches to knee OA aim to reduce the KAM. We previously reported that flat flexible footwear may reduce the KAM compared to wearing conventional footwear.  However, the characteristics of conventional footwear that influence the magnitude of this reduction remain unclear. Here we evaluate the footwear of participants with knee OA to identify the properties associated with response to a flexible footwear intervention. 

Methods: Participants with medial compartment knee OA were provided with a flexible study shoe (previously described “mobility shoe”) and were asked to bring their own conventional shoes that they used most often for walking activities.  Their own shoes were evaluated for stability/flexibility with the following 3 tests: 1) Sagittal stability: the shoe was held perpendicular to a flat surface with the tip of the toe on the ground and approximately 5 pounds of load was applied vertically on the heel; 2) Torsional stability: the shoe was held parallel to the ground with a hand at the heel and the toe and about 5 pounds of torque was applied;3) Heel counter stability: about 5 pounds of force was applied to the medial and lateral heel counter using the thumb and index finger. With all three tests, the resistance to deformation was classified on a 3-point grading scale (0: rigid, 1:supportive, 2: flexible).  The heel height of the shoes was also measured.  Gait analyses were performed while walking in subjects’ own shoes and the flexible study shoes.  Paired t-tests were used to evaluate overall percent reduction in the KAM with the flexible footwear compared to participants’ own shoes, and the association between reduction in the KAM and measures of their own shoe flexibility/stability was evaluated using Spearman’s coefficient. 

Results:  22 participants (15 women, mean age (SD) of 62±11 yrs) were evaluated.  Overall, the use of the flexible study shoes was associated with a significant 6% reduction in the KAM (2.55±1.00 vs 2.40±1.00 %BW*ht, p=0.007).  The percent reduction demonstrated in the KAM was significantly associated with the sagittal (rho=-0.470, p=0.027), torsional (rho=-0.470, p=0.027), and heel counter stability (rho=-0.551, p=0.008) of the participant’s own shoe, with more rigid footwear being associated with greater KAM reduction.  The assessments for sagittal and torsional stability did not appear to provide unique information since they were strongly correlated (rho = 1.0) with one another.  Interestingly, heel height was not associated the extent of KAM reduction (rho=0.181, p=0.488).  

Conclusion: Footwear has been associated with knee joint loading and choice of footwear may be an important consideration in knee OA.  This study suggests that those wearing more rigid footwear may expect the greatest benefit in medial knee load reduction with transition to flexible footwear and supports the concept that flexibility is an important load-reducing feature of footwear.  Simple protocols to evaluate footwear such as those used in this study may be beneficial in helping patients make choices regarding footwear.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characteristics-of-conventional-footwear-and-their-association-with-reductions-in-knee-loading-with-a-flexible-footwear-intervention/