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The aim of this work is to develop an automatic computer method to distinguish between asymptomatic (AS) and osteoarthritis (OA) knee gait patterns using 3-D ground reaction force (GRF) measurements. GRF features are first extracted from the force vector variations as a function of time and then classified by the nearest neighbor rule. We investigated two different features: the coefficients of a polynomial expansion and the coefficients of a wavelet decomposition. We also analyzed the impact of each GRF component (vertical, anteroposterior, and medial lateral) on classification. The best discrimination rate (91%) was achieved with the wavelet decomposition using the anteroposterior and the medial lateral components. These results demonstrate the validity of the representation and the classifier for automatic classification of AS and OA knee gait patterns. They also highlight the relevance of the anteroposterior and medial lateral force components in gait pattern classification.

The article presents a simple and rapid method for the correction of electromagnetic distortions when using electromagnetic Fastrak (Polhemus, USA) sensors. It is based on the minimization of objective functions composed of derivative polynomial functions, hence estimating the distortion of the electromagnetic field. The polynomial functions composing the objective function each contain 35 deformation coefficients. These coefficients are then used to correct the electromagnetic measures in position and orientation. Preliminary results on the efficacy of the method are presented for two subjects who walked on a treadmill, and for whom relative movement of the lower leg with respect to the thigh was recorded using two Fastrak sensors. The corrected Fastrak measurements were compared with optoelectronic measurements (Vicon, USA), which are not affected by distortions as electromagnetic sensors are. Results showed that after 3 min of calibrating a volume of approximately 1m(3), the method proved to be efficient in correcting errors in orientation (56% (2.72-1.12 degrees ), 78% (4.4-0.89 degrees ), and 56% (2.25-0.90 degrees ) of error reduction in the respective flexion/extension, ab/adduction and tibial internal/external rotation) and position (53% (18.9-8.9 mm), 21% (6.6-4.6mm), and 48% (15.9-8.1mm) of error reduction in the respective medial/lateral, anterior/posterior and proximal/distal translations) (values are overall means for two subjects and four calibration procedures). That amount of correction compared favorably with values presented in the literature.