Abstract
ObjectiveBiomechanical effects of laterally wedged insoles are assessed by reduction in the knee adduction moment. However, the degree of reduction may vary depending on the reference frame with which it is calculated. The purpose of this study was to clarify the effect of reference frame on the reduction in the knee adduction moment by laterally wedged insoles.MethodsTwenty-nine healthy participants performed gait trials with a laterally wedged insole and with a flat insole as a control. The knee adduction moment, including the first and second peaks and the angular impulse, were calculated using four different reference frames: the femoral frame, tibial frame, laboratory frame and the Joint Coordinate System.ResultsThere were significant effects of reference frame on the knee adduction moment first and second peaks (P < 0.001 for both variables), while the effect was not significant for the angular impulse (P = 0.84). No significant interaction between the gait condition and reference frame was found in either of the knee adduction moment variables (P = 0.99 for all variables), indicating that the effects of laterally wedged insole on the knee adduction moments were similar across the four reference frames. On the other hand, the average percent changes ranged from 9% to 16% for the first peak, from 16% to 18% for the second peak and from 17% to 21% for the angular impulse when using the different reference frames.ConclusionThe effects of laterally wedged insole on the reduction in the knee adduction moment were similar across the reference frames. On the other hand, Researchers need to recognize that when the percent change was used as the parameter of the efficacy of laterally wedged insole, the choice of reference frame may influence the interpretation of how laterally wedged insoles affect the knee adduction moment.
Highlights
Knee osteoarthritis is one of the most common orthopedic diseases, affecting up to 30% of individuals over the age of 65 [1]
No significant interaction between the gait condition and reference frame was found in either of the knee adduction moment variables (P = 0.99 for all variables), indicating that the effects of laterally wedged insole on the knee adduction moments were similar across the four reference frames
The average percent changes ranged from 9% to 16% for the first peak, from 16% to 18% for the second peak and from 17% to 21% for the angular impulse when using the different reference frames
Summary
Knee osteoarthritis is one of the most common orthopedic diseases, affecting up to 30% of individuals over the age of 65 [1]. The external knee adduction moment (KAM) is a valid and reliable indicator of medial compartment load [4, 5], and correlates to knee pain [6] and radiographic disease severity [7]. It is a predictor of initiation and progression of the disease [8]. Wedged insoles were first proposed by Tomatsuri et al to treat medial knee osteoarthritis [9]. Biomechanical studies report that lateral wedges reduce the KAM during gait in healthy participants and patients with medial knee osteoarthritis. The KAM increased while using the insoles in 13% to 18% of knee osteoarthritis patients, while it decreased in other patients [13, 14]
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