Ankle motion may predict who will respond to lateral wedge insoles

Lateral wedge insoles are a potential simple treatment for medial knee osteoarthritis (OA) patients by reducing the external knee adduction moment (EKAM). However in some patients, an increase in their EKAM is seen. Understanding the role of the ankle joint complex in the response to lateral wedge insoles is critical in understanding and potentially identifying why some patients respond differently to lateral wedge insoles.

To our knowledge, this is the first study to demonstrate that it is possible to distinguish if an individual is likely to decrease their peak EKAM when wearing lateral wedge insoles.

Predicting and/or identifying if an individual is likely to benefit from an intervention is an important issue. In the present study, we attempted to determine if it is possible to predict those individuals that are likely to respond to lateral wedge insoles (i.e., decrease their peak EKAM; biomechanical responders) compared to those that will not respond (biomechanical non-responders), by using coronal plane ankle/STJ complex biomechanical variables within the control condition. Our findings demonstrated that those individuals that have a greater everted ankle/STJ complex under the control condition were more likely to decrease their peak EKAM under lateral wedge conditions.

This finding may be counter-intuitive given that those individuals that have a more inverted foot could potentially have greater range to rotate their foot into eversion. However, the present findings suggest that those patients with a more everted foot are more likely to be shifting the centre of foot pressure more laterally, thus potentially reducing their EKAM compared to those with a more inverted foot, a finding that is consistent with other past biomechanical studies examining foot posture and knee loading.

Taken together, these findings suggest that those patients with a less everted ankle joint complex under control condition may have restricted frontal plane ankle range of motion, thus when a lateral wedge is inserted into their shoe, the restricted ankle range of motion may not allow the ankle joint complex to evert/pronate sufficiently to alter the load at the knee. However, due to the omission of clinical data, this is only a hypothesis and an area that future research needs to focus on.

Ankle motion influences the external knee adduction moment and may predict who will respond to lateral wedge insoles?: an ancillary analysis from the SILK trial, Chapman GJ, Parkes MJ, Forsythe L, Felson DT, Jones RK. Osteoarthritis Cartilage. 2015 Aug;23(8):1316-22. doi: 10.1016/j.joca.2015.02.164. Epub 2015 Mar 5.

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