Category: Applied Functional Science
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Hsu, W-H, Lewis CL, Monaghan GM, Saltzman E. Hamill J, Holt KG. Orthoses posted in both the rearfoot and forefoot reduce moments and angular impulses in the lower extremity joints during walking. Journal of Biomechanics, 2014, 47:2618-2625.

This article looked at the alterations in lower extremity motion during walking produced by a foot orthosis posted medially under both the rearfoot and the forefoot. The authors note that previous research on the mechanical effects of foot orthoses has been equivocal. They propose that some of the variance in research findings might be attributable to insufficient posting under the forefoot – more specifically, a post that would extend beyond the metatarsal heads. The 15 subjects were identified to have a forefoot varus greater than 10 degrees, but without lower extremity pain at the time of the data collection. Subject data was collected at two occasions: at the time of the orthosis fabrication and after having worn the orthoses for one week. The data was collected wearing sandals so that the segments markers could be attached to the foot instead of a shoe allowing investigation of motion of the forefoot.

With regard to foot biomechanics, the orthosis condition showed decreased peak eversion angle of the forefoot and delayed occurrence of the peak eversion. At the ankle, the peak joint inversion moment and the angular impulse were reduced. Slightly different from the author’s expectations, the effects on the knee were “not as strong as predicted,” but “the effects on the hip were remarkable.” This blog will focus on the changes in hip biomechanics with the orthotic intervention. In the frontal plane, the maximum adduction angle as well as the maximum internal abduction joint moment were “significantly reduced.” This demonstrates the efficacy of the medial (frontal plane) correction of the orthoses on frontal plane kinematics and kinetics of the hip.

The findings in the transverse plane are also important because they verify the transformation of frontal plane foot motion into transverse plane hip motion that occurs at the subtalar joint when the foot is on the ground. The maximum internal rotation angle was reduced and the external rotation joint moment and angular impulse were decreased. Because the changes in foot motion occurred along with the changes in hip motion, this signifies that an orthotic intervention at the foot can produce substantial corrections in the hip. The angle of the subtalar joint axis creates this “mechanical truth,” and the relationship works both from the foot to the hip, and from the hip to the foot. This last statement means that transverse plane hip motion will create a frontal plane foot reaction when weight-bearing. 

The results of this study are important because it demonstrated the efficacy of foot orthoses to influence foot/ankle and hip motion with orthotic posting that extends under the medial forefoot in the forefoot varus group. It provides documentation of the frontal and transverse plane motion of the hip during walking, and how it is influence by a foot orthoses. The unexpected finding that the knee motion was less influenced than the hip is consistent with Dr. Gary Gray’s description of the knee as the joint between the foot and hip that “has few places to go and nowhere to hide” from the forces of multi-joint function. 

For the movement practitioner the results suggest (in conjunction with other studies) that correction of excessive motion and reduction of tissue stress requires an orthoses that “matches” the structural foot deformity. More globally, it reminds us of the Principle of Chain Reaction® that forces us to look elsewhere in the kinematic chain to find the cause of patient symptoms and dysfunction. Asymptomatic impairments throughout the body can alter the joint motion and tissue stresses anywhere in the movement chain. Appreciating this fact, expands our list of probable suspects (causes), and at the same time expands the strategies available to correct the impairments, eliminate symptoms, and restore function in our patients and clients.

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