Detecting differences between asymptomatic and osteoarthritic gait is influenced by changing the knee adduction moment model

Introduction The adduction moment measured at the knee during gait is important to the study of osteoarthritis. The purpose of this study was to explore the effect of describing the knee adduction moment using three different biomechanical models, and furthermore, how the choice of model affects differences that are identified between asymptomatic and osteoarthritic gait. Methods Gait was measured for 44 asymptomatic subjects and 44 subjects with moderate osteoarthritis. The adduction moment was calculated and compared using three common biomechanical models: a 2D coordinate system, a 3D tibial coordinate system, and a 3D floating axis coordinate system. Several portions of the gait cycle waveform were compared between the two groups. Results and discussion It was found that the choice of biomechanical model changes the overall magnitude and shape of the adduction moment waveform (maximum value changed 8–14% and peak value changed 5–17%). Significant differences between the study groups were found for each model applied; but more importantly, the portions of the gait cycle exhibiting the differences depended on the model. Conclusion These findings support the importance of specifying the knee model and waveform feature used to compare asymptomatic and osteoarthritic groups. The overall magnitude of the adduction moment throughout stance, and the mid-stance adduction moment value were found to differentiate between the two groups regardless of the adduction moment model.